It may seem a little embarrassing to ask, but in case you were wondering, we’ll answer it – Do fish eat poop, and if so, what fish?


Do fish eat poop?

They might, but they probably don't. You may sometimes see a fish nibble on poop from other fish, and fish do have a tendency to eat whatever they see floating in the water column – but they also have a tendency to spit non-food items back out (including poop). Some animals, such as rabbits, may eat faeces as a “2nd round” of nutrition and it’s entirely possible that a fish might ingest some poop that they mistook for other foods – but this isn’t necessary for their nutrition and isn’t likely to help out with your tank health (we’ll talk more about this soon).


Platy fish  

Above: The Platy Fish (Xiphophorus sp.) - Good at making poop, not good at eating it.


What fish eat poop?

As far as we are aware, there are no freshwater fish that have poop as a necessary part of their diet. Some fish such as Corydoras and Plecostomus catfish are said to eat poop – but even if they did, they still require feeding just as any other fish would. Although it might depend on what fish processed it, the products left in poop are mostly waste – meaning there isn’t much left that’s useful to the fish that decides to nibble on it.


But won’t their poop-eating help my tank health?

It sounds like a cool idea, but unfortunately it isn’t going to do a whole lot for your water quality. As mentioned above, even if a fish does eat poop, it still requires a sufficient high-quality diet. This, mixed with waste being a natural part of any living being, the fish eating the poop is still going to poop! Only they’re going to add to the amount of poop in the tank, as they are extra fish that still need to be fed.

Not only that, most of the nitrogenous wastes (such as Ammonia) are actually excreted via the gills, not poop[1][2]! While it’s still important to remove physical wastes such as poop from the tank when possible, Ammonia production will still happen regardless of how much poop is produced or eaten.


How do I get rid of poop, then?

There is something that will eat poop – a good siphon. This is a key method of removing debris from your tanks water column and substrate. Regular cleaning of pre-filter sponges (our personal preferred method) and mechanical media are also important methods to remove debris build-up, thus removing excess waste and allowing for better flow of water to your beneficial bacteria (which are essential for converting that Ammonia).


bristlenose plecostomus pleco

Above: The Bristlenose Pleco (Ancistrus sp.) - Also good at making poop, still not good for eating it.


In Conclusion

Whilst there aren’t really any fish available purely for the purposes of eating poop, fortunately poop-eating fish wouldn’t be that useful for your tank health anyway. You can still add those Corydoras or Plecos (provided your tank is suitable) as they are fascinating fish to keep, but unfortunately they won’t quite do the job of cleaning up (that part is up to you).

We hope that this article may be of some help when making the decision of whether you add some poop-eaters! Have any questions? Feel free to Contact Us!


[1] https://cyber-aquaculture.wikispaces.com/The+Nitrogen+Cycle
[2] http://vetsci.co.uk/2010/05/15/comparative-nitrogen-excretion/

Rack of Testtubes

Learning the tank cycle can be a long and confusing process, but bear with me! I would consider understanding the tank cycle to be the most essential part of fishkeeping, and you certainly won't regret learning about it. An uncycled tank can be dangerous and even lethal for your fish, as ammonia will quickly harm and kill any fish living in even small concentrations.

The Cycle is what happens in your filter. Filters can be internal, external (canister), hang on back (HOB) or even an extra tank called a 'sump'. Within the filter you have what's called filter media. This media comes in lots of different forms - some common forms are:

  • Ceramic noodles
  • Plastic 'bio' balls
  • Filter wool
  • Filter sponge/foam (coarse and fine)
  • Pumice, scoria and glass 'rocks'
  • Activated carbon (sometimes in the form of filter sponge)

The bolded media is commonly used as what's called 'biological media' (because of the large amount of 'clingable' surface area). The un-bolded media is commonly used as what's called 'mechanical media' (allows for good flow, catches particles and waste). The biological media is what we'll be discussing in this article.


Within your biological media is lots of gunk (what we refer to sometimes as 'marmite', and you can see why after a month of running a filter!) which contains good bacteria that will work on your cycle. There are two types of bacteria in this - the bacteria that turns ammonia into nitrite, and then the bacteria that turns nitrite into nitrate.

I'll get to the technical bits in a second, but this next bit is very important: do not go cleaning your filter weekly! This was the first thing I and many others did when we started fishkeeping. A clean filter is a clean tank, right? Surprisingly, nope! Because your good bacteria live on the biological media, it needs to stay there. Sometimes you need to clean your filter to stop the 'gunk' from building up - when you do this, it's best to only clean the sponge/foam or 25% of the 'mechanical' media. This means you clean out any built-up waste without harming too much of the good bacteria. If you clean out the biological media, you risk killing all the bacteria on it which causes the tank to go into a 'mini cycle'. When rinsing the mechanical media, it's important to do so in the old tank water from a water change, so that no cold/chlorinated water kills any remaining bacteria.


So wait, what was all that gibberish?

When your fish create waste, they excrete what's called ammonia. Ammonia (NH3, or ammonium, NH4+) is incredibly toxic to fish, and needs to be turned into something else. Your first set of bacteria do just this, and turn the ammonia into nitrite. Nitrite (NO2-) is the second part, and is also quite toxic! The second set of bacteria quickly get onto this, and turn that nitrite into nitrate. Nitrate (NO3-) is the final part of your cycle. nitrates are then able to be removed through both water changes and plants, although you need a very heavily planted tank to remove equal or more nitrates than what are being produced, and even then water changes are necessary to re-add minerals in the water which are important for the plants and fish.


So, how do I get these bacteria?

The process of cycling is how you get these bacteria. You can cycle in three ways: Fishless cycling, Fish-in cycling, and Pre-seeded bacteria.

Fish-in cycling can be considered cruel, as even the hardiest fish can be heavily affected by the ammonia produced (as, remember, there aren't any bacteria yet to convert it) and ammonia burning can have long-term effects on the fish such as 'ammonia burns' to the gills. For this reason, I don't encourage fish-in cycling. However, for some it can be too late, and for that, don't panic! It just means you'll have to do a bit more work than usual. Over the next few weeks, your filter will cycle itself through the waste produced by the fish. This form of cycling simply means you need to do daily water changes to make sure the ammonia stays to an 'acceptable' level. Water changes will help dilute the ammonia and reduce the stress on the fish - however, this means that the cycle may take longer than usual, and it is important you don't add any new fish until the cycle is finished (and once it is, add them in very small amounts to not shock the system).

Fishless cycling is my preferred method of cycling. This method is super easy, and requires very little maintenance. In order to create and feed the bacteria, you need to be producing waste. There's a couple of ways you can do this:

  • You can 'feed' the tank ammonia on a daily basis. Pure ammonia can be bought from your local supermarket - just make sure it doesn't contain any extra nasties! There isn't a real guide on how much to feed the tank, but it doesn't matter too much as there's nothing currently living in it.
  • Literally feed it! On a daily basis, feed whatever you would be feeding your fish to the tank and let it rot.
  • My chosen method: Putting a prawn in the tank. Put a prawn in a filter sock or some pantyhose (just to keep it in one place) and let it rot in the tank for the next few weeks. This means you can leave the tank running without any maintenance, although I like to do a 100% water change (remember your de-chlorinator!) afterwards to clean up any mess.

Seeding the filter is possibly the easiest way to go, but you need to have some handy. Simply take about 25% of the media (and replace it with new media) from an already established filter, and put it into your new filter. I like to run the dechlorinated water through the filter for about a day before adding the seeded media, just to make sure it isn't shocked by the new water. After this, you can add fish instantly! Be careful as to only add a few fish (or inverts) at the beginning, as your bacteria need to spread to the rest of the filter material, but it's also important to add fish as soon as possible or to continue to feed it until you add fish as the bacteria will quickly die without anything to feed on!

Almost all of my tanks came from the media of my first ever tank, and I have never had any issues with pre-seeded filters, however as you would with the other methods it's important to test your water for the first week to make sure it's safe for the fish!


How do I tell if I've finished cycling?

When you first start the cycle you'll expect to find high ammonia. Then you'll find some ammonia, and some nitrites. You may then find some ammonia, nitrites and nitrates - then nitrites and nitrates, and then simply nitrates. Once you find nitrates, your cycle is finished! Here's a chart of what your cycling tank may look like:



Once cycled, your tank should then test these levels - if they're not like the ones below, it means your tank is still cycling. If you have an established tank which is showing the levels below, it could mean that your tank is either overstocked, your filter is not strong enough or your tank is going through a 'mini cycle' (where for some reason the bacteria has died and needs to cycle again) -

Ammonia: 0ppm

Nitrites: 0ppm

Nitrates: 5-20ppm

Even the heavily planted tank rarely has 0 nitrates, and no nitrates could actually mean you may have tested wrong (don't worry, the nitrate test can be confusing!). Most fish will be OK with nitrates up to 60ppm, but nitrates above 20ppm can stunt growth and stress a fish out, which means that diseases might thrive on your fish. Sensitive fish such as Otocinclus spp. can even die in nitrates above 40ppm. Some other fish will handle nitrates up to 80ppm! All fish are different, but as a general rule nitrates shouldn't go above 20ppm. If in doubt, do a water change, as will help lower your nitrate levels and give your fish fresh, clean water.

Note that some tap water can have nitrates up to 40ppm, but most sits around 5-10ppm. Having nitrates of 40ppm simply means that it is advised to not keep very sensitive fish, unless you are interested in running the water through a clean planted system to help lower the nitrates before it goes into your tank.


What do all these colours mean, and how do I test these levels?

The colours on the chart above are based on API's Test Kits which are available from most pet stores. The liquid test kits are by far the most accurate way of testing your water, as the 'paper dip' tests or 'stick on' tests are often unreliable and could lead to the death of your fish if they fail. These tests are simple and easy to do, and are good to do on a weekly basis (and should especially be the first test done if a fish ever shows sign of illness).


A note, however, is to take extra care when doing these tests. If dosed wrong, they may give false readings, leading you to think your levels are either safe when they are not, or too dangerous! A difficult test to do is the nitrate test, and is the one I most often see done wrong. Read and follow all the instructions carefully — it is very important that the second bottle is shaken for the time instructed, and that the test tube is shaken and left to sit for 5 minutes before getting your results. I've even seen someone who was getting 0 nitrates, when they had nitrates over 120ppm! But don't worry if you get it wrong the first time - it was a while before I realized they were giving me false readings, too.

These test kits are a bit pricey, but in the end they are every fishkeeper's best friend. If you cannot afford one now, most pet stores are happy to test your water for free. If you have one right now, go test your water! You may be surprised as to what your readings are.


In conclusion, the cycle is an extremely important part of fishkeeping and it is important you understand it. If anything is confusing, don't panic, as it is often confusing to everyone when they first read it. Don't be afraid to ask questions, and feel free to message us, or ask your local fishkeeping forum!

Wait up! Before you buy that adorable Oscar fish and put him in your 50L tank, there's a few things you need to consider - some of which could save both your new fish and your current ones!


Will my new fish be suitable for my tank?

- How big is that fish going to get? It's important to give a fish as much space as needed for it to get to full size; even when putting fish in holding tanks temporarily, some fast growing fish can become stunted if in there for too long! For example, one of the most popular fish in aquaria is the goldfish. You've seen them everywhere - in adverts, TV, even in your friend's home! But you've probably also seen them in the worst possible setups - bowls! All goldfish get over 20cm big - some will tell you that this is OK as fish only grow to the size of their tank, but this is a myth! While its skeleton will grow to the size of the tank, the fish becomes gross and deformed - spines can bend, heads will go a funny shape and so-forth. So make sure your tank is big enough for the adult size of the fish you're getting! Sometimes "grow out" tanks are used, but this depends a lot on the fish you're growing and whether you already have a tank suitable for adulthood - remember, circumstances change and you have to be prepared to care for your fish for its entire life!


Above: Spiny eels such as the Fire Eel can grow to one metre in length!


- How long does the fish live? This isn't something you often consider when buying fish - often people think most fish usually live around 2-5 years. While this is true for many small fish, some live much longer than that! Are you prepared to look after a fish for the next 10-50 years? Yep, that's right, 50! Clown Loaches are often sold to new fishkeepers, but people forget to mention that some have recorded that these popular fish can live from 50 to 60 years!

- What is the bioload of this fish? That pretty much means "How much does this fish poop?" - sometimes even the smallest fish eat more food than others their same size. A common example is the Bristlenose pleco. Bristlenoses are vegetarians who have the nickname of being "poop machines" - just see how much one can produce when in the bag coming home from the pet store! High-bioload fish can produce a lot of waste for small tanks and thus a lot of filters aren't prepared to deal with the sudden increase. If the filter is too small or there is too little flow, the waste produced will turn into ammonia and can quickly harm your fish. When the filter is adequate, these fish will still mean the tank needs more water changes than before! This is because of Nitrates, which are produced at the end of your filter's "cycle" - the main way to remove these are through water changes, otherwise if they build up they can also harm your fish! (Note: expected levels of nitrates are between 5-20ppm, many fish will handle 40-60ppm however levels over 80ppm can be dangerous for most fish!)


Bristlenose Pleco Ancistrus

Above: Commonly sold, the Bristlenose Pleco needs a good filter and regular water changes.


- Does this fish get along with my current ones? All fish are different and can range from the timid killifish to the boisterous and aggressive oscar! Some fish with long fins are delicate and timid (eg. the betta), and can quickly become stressed around active and nippy fish (eg. barbs). Some fish need to be on their own because of how shy they are and how they can easily be out-competed for food, others need to be on their own because they'll kill anything in their sight! It's also important to keep in mind of temperament changes; for example, dwarf cichlids such as rams can become aggressive when breeding, or some fish become aggressive as they age.

- How many do I need? Many fish need buddies to keep them happy - without other fish, they can become lethargic and "depressed". For social and schooling fish, other fish of the same species provide both socialization, mates and a strong sense of security. When providing a good schooling size for fish you are more likely to see your fish out and about and more willing to allow you near! This is a very common issue, as many people don't realize how important it is to provide the proper schooling size for fish. For example, tetras are well known to be schoolers but people sometimes only keep 1-5 of them, and then wonder why they're shy! When keeping schools of 7+, they are more likely to be happy and safe, thus letting you come near and watch them. The best schools can be those of 20-30+ fish - in the wild, a lot of fish will hang in schools of over 50! Many always find tanks more interesting with one large school of fish, than those with many small schools of different species.

Being aware of the ideal female:male ratio is also very important. Some fish are very territorial and will not tolerate a second male in the tank (a good example is the Siamese Fighting fish, where males will fight and even kill each other). Others will tolerate having multiple males (such as tetras and other shoaling species). A good ratio to keep in mind is 1 male to 2-3 females. When keeping fish long-term, it's often better to have trios rather than pairs, as this helps to reduce the stress on females which are frequently picked on by their male counterparts!


Otocinclus Oto

Above: Often sold as an efficient algae eater, otocinclus are happiest in schools of 5 or more


How to make my tank suitable for my new fish?

It's important to make your new fish feel like they're at home. When you replicate the conditions that it would live in in the wild, you will often see an increase in natural behaviours and general happiness of your fish.

- What are the preferred water conditions for my fish? Some fish such as African Cichlids prefer a high pH above 8.0, but other fish such as some Gourami sp. come from pH as low as 4.0! Fish from low pH environments also have waters stained with tanins which is achieved by leaf litter and driftwood. Other things to consider are temperature, water hardness and how sensitive the fish is. Some fish can become stressed if their nitrate levels exceed 20ppm, others can handle nitrates up to 100ppm!

- What's the natural habitat of my fish? Important things to consider are:

- Substrate: For example, loaches and catfish such as the kuhli loach and corydora sp. will have natural behaviours such as digging and foraging for food in sand. It's very exciting to watch them sift and dig as they search for food! It is also noted that corydoras kept on sand tend to have longer "barbels" than those kept on gravel, as they are worn down against the harsh surfaces.

Aphyosemion australe gold killifish

Above: Killifish can freak out with light substrate and prefer dim lighting and lots of cover plants!


- Flow: some fish can become anxious and stressed in too little or too much flow. Fish such as minnows will spend a lot of time happily swimming against the filter output - for them, the more flow, the better! Others such as puffers have poor finnage, and come from still waters - too much flow can stress them out as they struggle to swim in it!

- Plants: Plants can help a fish feel safe and provides lots of places to hide and swim throughout. Fish love exploring through plants and plants help to provide breaks in the line-of-sight for fish to help keep aggression down and providing territory. Many fish come from densely planted areas, so plants will certainly help them feel at home!


Killifish planted scape

Above: A heavily planted tank has many benefits, including allowing fish to feel secure and at home!


- Hiding places: Does this fish come from places surrounded by rock or wood? Decor will help to provide places for fish such as catfish to hide and even breed! Some fish such as some pleco species even use wood in their diet!

- Lighting: I often forget this one! Make sure your lights aren't too strong or weak. For example, some fish come from very shaded areas and therefore strong light can make them feel exposed and unsafe. Good ways to counteract this is to have lower light outputs (such as dimmable LEDs or T8 lighting) or to have dense cover planting (such as mosses and duckweed).


Above: Fish like dwarf puffers prefer lower lighting such as low-power LEDs or T8s


- How do I keep my fish from getting wounded? It's important to keep your tank safe for your fish. Scaleless fish are prone to wounds and burns, so a heater guard and smooth decor is preferable! Long finned fish typically need low flow and can easily tear their fins on sharp rocks and decorations such as some fake plants.


Other Things to Note

Also important making sure the fish you are buying are healthy! Never buy a fish from a tank which has other sick or unhealthy fish in it. Things to look out for are: White spots, lethargy, fungus/fuzzyness, wounds, fin rot and malnutrition. Buy fish that are healthy and active, and will respond positively to your movements (eg. fish that come towards the tank for food, versus fish that swim away in fear - note that some fish are naturally timid, however). For fish such as wild caught fish, parasites are common and it can be useful to ask the staff whether they can feed the fish in front of you to make sure they're eating correctly.


It certainly seems like a lot to consider when you first start off, but soon enough it'll become second nature and you'll even learn to figure out basic needs from simply looking at the fish! It can feel overwhelming, but a good idea is to go to your local fish store and write down the names of all the nice fish you see. Then bring the list home and go through and google all the different species. Then write down a stock list of what fish are compatible and before you know it you'll know exactly what you want in your tank! Knowing your stocking list helps you avoid impulse purchases and therefore means all your fish can live in harmony!


Have any more things to consider before purchasing fish? Feel free to contact us, or ask your local fish forum!


Table of Contents:



So, you have a small tank and you've been told that that large Pleco isn't suitable. What else can you put in it?

This is probably one of the most common questions I encounter, and it is one of the most difficult questions to answer. It would seem logical to think that the smaller the tank, the easier it is to maintain, however the complete opposite is true. In fact, small tanks can be so difficult to maintain they become somewhat of a specialist category, "Nano tanks". The main reason for this is waste control, which leads to high Nitrate levels and often algae problems. The following may seem a bit like gibberish at first but it's important to understand:

Let's say a fish makes 200mg of Nitrates in a week, in a 20 Litre tank that makes 10mg/L, around 10ppm Nitrates. In a 27L tank, however, it becomes 7.5mg/L, around 7.5ppm Nitrates. If you want to keep around 5ppm Nitrates, you would have to do a 50% water change in the first 20L tank to achieve this, however in the 27L tank you would need to only do a 25% water change. Here's a visual image of how this may work:

water change example 01


Basically, Bigger Tanks = Easier To Keep

It may feel like you're using an awful lot of space for such a small fish, but the fish kept in these small tanks are so often full of such personality that the "empty space" no longer becomes a problem. Bigger tanks allow for more options for decoration, meaning more places to put plants, rocks, driftwood and decor of your choosing! The amount of water provided in these tanks can also often be a lot smaller than what the fish experiences in the wild, so bigger is certainly better. Here at Fishwise we recommend 21 Litres as a minimum for the majority of fishkeepers, due to the ease of maintenance and care, along with allowing for a good amount of space per fish.


What makes a good "Nano" fish?

This is the key question, and one that is under a lot of debate. Some people say that Nano tanks are a new phase, however people have been (wrongly) keeping goldfish in bowls for decades - it appears we're simply choosing more appropriate fish, and giving them better conditions. It's important to note that bowls are rarely a suitable home for a fish. You can read about the concerns with bowls here. So, what is there to consider when deciding whether a fish is appropriate for a small tank?

- Size. This may seem like an obvious one, but years of goldfish in bowls shows that may not be the case. It's important that the fish doesn't outgrow or isn't stunted by the amount of space given. While that unfortunately means that your 45cm Oscar isn't quite appropriate for a 30L tank, but some 3cm Hara catfish would be perfect.

- Shoal Size. A fish that requires a shoal of, for example, 15 individuals will need a lot more space than a single solitary fish. Remember, the more fish; the bigger the bioload, meaning larger and more frequent water changes will be necessary, making a larger tank preferable for some.

- Activity Levels. Busy fish like Neon tetras may not be suitable, as the require lots of room to dart around. A more "peaceful" Betta however has lower energy levels and may not require as much space to swim around in.

- Aggression Levels. Some fish simply will not allow others in their territory, or become aggressive towards fish such as them. An example once again is the Betta fish which is particularly aggressive towards other colourful and longfinned fish, although individual personalities may vary. Other fish such as Puffer fish may not allow conspecifics (fish of the same species) in the same tank.

- Bioload. Some fish have larger bioloads than others - vegetarians are common for this! Bristlenoses are one common fish known for their large bioload, and are often referred to as "Poop machines". Because of this, their size and aggression levels they are unfortunately unsuitable for the Nano tank. A large shoal of fish will likely have a larger bioload than a single fish and thus may need more space for ease of water quality maintenance.

Killifish planted scape

Above: A 55L Nano Killifish Tank


What is a "Nano" Tank and How do I Look After It?

The Nano tank doesn't require significantly different care to regular tanks but it does tend to require a bit more maintenance. The definition of the word Nano differs between people, but for the purpose of this article it is a tank that ranges between 21 Litres - 55 Litres. As mentioned above, the major difference between Nano tanks and regular tank sizes is that keeping water parameters stable is more difficult in the Nano tank and these tanks tend to require either water changes of 25% twice-weekly or 50% once weekly. Whether the water changes are done once or twice weekly depends on the sensitivity of the fish (some prefer smaller water changes) and your personal schedule and how much time you are willing to dedicate to the tank. For busy people, 50% weekly may be easier. For larger water changes it is recommended to keep an eye on parameters such as pH and Water Hardness to keep them similar. For example, in a tank with a pH of 6.6 and hardness of 5dKH* it would be best to do smaller water changes (eg 25%) if, for example, your pH is 7.8 and 10dKH to avoid any kind of shock or need for the fish to acclimate to the change in conditions. It is easier to do a large water change (eg 50%) when your pH and Hardness are similar between the tank and tap water. This also depends on the fish and their preferred range.


The reason for these large or frequent water changes is because of that mentioned above - fish in smaller tanks create more waste per Litre. This is recommended in order to keep your waste levels (Nitrates) low in order to keep your fish healthy and to prevent algae growth. Algae grows in environments of high waste and keeping the waste levels down (along with other nutrients) helps to keep this growth at bay.


Keeping your Nano tank planted can have a significant benefit for both the fish and algae levels. Plants help to take up extra nutrients (nutrients from your tap water and nutrients created by the fish), which prevents algae growth and keeps your tank nice and clean. This allows for less frequent maintenance, including less frequent water changes! Plants also provide plenty of places for your fish to explore and hide, which helps to prevent stress and boredom. Many Nano fish prefer densely planted tanks and this helps to keep them feeling safe and secure.

Substrate is also important and it is good to keep in mind what your fish prefers before setting up the tank. Fish such as Killifish often prefer darker substrates, which makes them feel safe. Fish such as Hara Catfish require sand, which keeps their barbels from being worn down and allows for them to display natural behaviours such as digging and foraging for food.

Flow rate is also often an important consideration for Nano fish. Many smaller fish prefer low flow rates, especially those with longer fins. Too high of a flow rate can stress a fish out, however it's important to try to have a good flow around the whole tank to prevent "dead spots" from forming (where ammonia, cold and low oxygen builds up and can create problems).

Lighting needs to be considered as many of the smaller fish species may come from darker areas where the water may be shaded by vegetation. Strong lights may stress these fish out and should be avoided. T8 tubes or LEDs may help to lower lighting while being able to grow plants, or if strong lighting is used, a floating plant cover like Indian Fern, Brazilian Pennywort and Duckweed can be used to keep the fish feeling safe and secure in its tank.

Filters may need to be larger for fish with larger bioloads such as Dwarf Puffers (Puffers are "messy eaters" and can leave a lot of uneaten food lying around). Larger filters allow for more beneficial bacteria to grow, which is necessary for fish that produce a lot of waste. More filtration also helps to prevent ammonia spikes if for example a plant rotted without being noticed, and allows for extra room for filter media such as chemical filtration.

*It is not entirely necessary to know your water hardness (GH and KH) unless you have very sensitive fish where it is important. It can be useful to know, however, and most local fish stores are happy to test your hardness for free. Hardness determines your pH and can, to an extent, affect the types of fish you can keep.


Finally: Suitable Nano Fish

I get all that, so now what can I actually keep in the tank?


21L and Over:


The Classic, Betta Fish (Siamese Fighting Fish)

Female Betta Steel Blue

Above: Female Betta Fish


Betta fish (Betta splendens) are your first recommendation for the smaller aquaria and are often recommended as "beginner fish". As with many fish, they are sensitive to water conditions, however they produce little waste and are the perfect option for someone getting used to maintaining a small tank. Betta fish come from a variety of conditions depending on the time of the year, but are often found in "rice paddies" and waters which have low flow and are full of dense planting. Contrary to popular myth, these fish may only spend a small amount of time in small bodies of water, typically during the dry season. These conditions are incredibly stressful and many fish don't make it, and a small jar or vase simply isn't a suitable long-term home for these (or any) fish. Bettas are often described as inactive, however when given the space they will certainly utilize it and explore when given the opportunity. Betta fish are Anabantoids, meaning they use a Labyrinth organ to "breathe" air, and use Bubble-nesting as a reproduction technique where they make many little bubbles at the surface to place eggs in which the male then guards.

The male Betta is typically sought after for his longer fins and flashier colours, however some find females just as fascinating. Bettas will quickly learn who their owners are and will often greet you as soon as you come near. These guys are full of personality and are sometimes even compared to having an aquatic dog or cat! Because of this, they are easily bored and prefer the well decorated tank with plenty of plants and hiding places to explore and keep them feeling safe. As many males have long fins and they come from slow-moving or even stagnant waters, it's recommended to have low flow as it can be stressful for them to have to battle lots of current. Lids are recommended as these guys are great jumpers and it's not uncommon to find one on the floor when kept without a lid. Betta are mostly insectivores, but will eat some vegetable matter on occasion. My recommended foods are live foods and Betta-specific pellets from your LFS.

In a 21L tank Bettas should be kept solitary, but in a tank of 38L or more a second species may be introduced. Betta fish can be quite limited in what they can be kept with, and there are a few basic rules around tankmates. It sounds difficult but there are still plenty of options available, predominantly bottom dwellers and small shoalers. Male Bettas shouldn't be mixed with other males or females, but females can be kept in a group called a "Sorority" in a larger tank (around 55L). Every Betta has an individual personality and some are so aggressive that they cannot be kept with tankmates, however most tend to do fine when tankmates are chosen with care. These are my rules for tankmates:

- Doesn't nip fins (due to Betta's slow movement and elaborate finnage)

- Doesn't have long, flowing fins (as Bettas will often nip at anything that looks like their species)

- Moves quickly (so that particularly aggressive Betta cannot nip at them)

- Doesn't have bright colours (so they cannot be mistaken for another Betta fish)

- No other Anabantoids (no gourami species for example, as these look far too much like Bettas)

- Not large or boisterous (as this can freak the fish out)

Some Basic Facts:

Minimum Tank Size: 21 Litres Compatibility: Semi-Aggressive
Maximum Size: 6.5-7cm Ideal Temperature: 25-30 Degrees C
Ideal pH: 5.0-7.8 Ideal Hardness: Soft-Medium Water
Diet: Predominantly Insectivorous Reproduction: Bubble-nester




Male Fundulopanchax gardneri gold killifish

Above: A Steel Blue (Fundulopanchax gardneri) Killifish 'gold'. 


This is a big category, but there are a few smaller species suitable for small tanks. Species such as Aphyosemion australe (Lyretail Killifish) and the Epiplatys annulatus (Clown Killifish) are small, have low activity levels and do well in trios, which makes them great fish for smaller tanks. They're also well known for being easy breeders! While they require little space, 3-5 fish can be a big bioload for a small tank, so it's important to keep on top of water changes for these guys. Smaller Killies are often shy little fish and they appreciate dense planting, including a "mop" of java moss which they will often readily breed on. They also tend to prefer darker substrate and low lighting in order to feel secure. A common trait for Killifish is being very capable of jumping, so tight lids are a must. Killies often come from soft waters stained heavily with tannins, so leaf litter, driftwood and peat will help them feel right at home.

Small Killifish tend to prefer species-only tanks as they are easily out-competed and scared off by busy fish. This can make it difficult to find tankmates, but the rules are very similar to that of fighters where fin nippers and longfinned fish should be avoided. The major difference in guidelines for tankmates is that because they are shy, smaller very peaceful shoaling species are preferred along with small and quiet bottom dwellers. It is also important to note that Killifish tend to prefer lower temperatures, making many tropical tankmates unsuitable. Killifish are usually social and the best setups tend to include the typical one male to multiple females, starting from 2 females and this number can increase as tank size gets bigger. It's best to have at least 2 females as males can be "pushy" when breeding and it helps to reduce stress on individual fish.

Killies are often insectivores and do best on a diet of a variety of live foods. Bloodworms, Daphnia, White worm, Brine shrimp and Blackworms will all be appreciated and quickly eaten up! Good live food also encourages them to breed regularly, letting you create your Killifish army in no time! All Killifish are sensitive to water conditions and good water quality is a must.

Some Basic Facts:

Minimum Tank Size: 21 Litres for a Trio or Breeding pair Compatibility: Peaceful, Shy.
Maximum Size: Various, small species between 3cm-6cm Ideal Temperature: Often 19-25 Degrees C
Ideal pH: 4.0-7.0 Ideal Hardness: Very Soft-Medium Water
Diet: Predominantly Insectivorous Reproduction: Mop-spawner


Dwarf Puffer

160605 dpf 4


Dwarf Puffers (Carinotetraodon travancoricus) are absolutely fascinating fish and are one of my favourites to keep. Puffers very quickly get to know you and certainly learn their biggest trick of begging for food! Dwarf Puffers (DPF) come from slow moving waters, dense with vegetation and hiding places. Just like the killifish they prefer dim conditions and may become stressed if the lighting is too strong or there is not enough cover planting provided. Unlike many other Nano fish, puffers tend to prefer Medium-Hard water rather than Soft water, so peat is not necessary but leaf litter may help to reduce stress and give places to hide. Puffers are highly aggressive almost strictly solitary, and the only other species that may not be killed are Otocinclus catfish which have been kept with success. Other puffers (of the same species) may be kept together however 55L minimum is recommended for a group of 3, adding 21 Litres per fish. 3 is recommended instead of 2 as this reduces the chance of an aggressive puffer picking on the other and injuring it.

There's a few things to keep in mind when bringing your puffer home. Despite their name, it's not normal for a Dwarf Puffer to puff up except in the most fearful of situations - once puffed, it can be difficult for the fish to deflate and can often be fatal. However, their tiny stomachs expand greatly when eating and easily gives the cute "puffed up" effect that they're well known for. Because puffing can be fatal, it is essential to not expose these fish to air and thus it's best to transfer them by cups rather than nets. It is also worth noting that these puffers are almost always wild caught and may carry internal parasites. It's definitely recommended to carry a de-wormer such as Praziquantel for your new puffer fish to help kill off any hitchhikers. Because of internal parasites, Puffers also often arrive emaciated (skinny) and it's a good idea to provide lots of quality foods to help fatten them up again.

Dwarf Puffers are carnivorous and should be fed solely live foods. Unlike other Puffer species, hard-shelled foods are not required to keep their beaks trimmed. However it is strongly recommended to keep a supply of snails to feed your Puffer as they are excellent, intelligent hunters and gut-loaded snails help to provide a good diet along with preventing boredom (which is often an issue in sparsely-decorated and empty tanks).

There are just so many things to learn about Dwarf Puffers but they cannot all

be covered in this section! An expanded article on Dwarf Puffers can be found here.

Some Basic Facts:

Minimum Tank Size: 21 Litres Compatibility: Highly Aggressive
Maximum Size: 2.5-3.5cm Ideal Temperature: 24-28 Degrees C
Ideal pH: 7.0-8.3 Ideal Hardness: Medium-Hard water
Diet: Carnivorous Reproduction: Spawns on vegetation such as moss


38L and Over:


Hara Catfish

Hara jerdoni catfish

Above: Hara catfish (Hara jerdoni)


Hara catfish (Hara jerdoni) are likely the smallest catfish available in New Zealand, reaching a maximum size of around 3cm. Even at night Hara cats are typically inactive, making them great Nano tank options. The downside however is that these fish prefer groups of 5 or more, meaning it's preferable to keep them in tanks of 38L and over to maintain good water quality (as like most of those on this list, these guys are also very sensitive to water quality). Hara cats inhabit slow moving, tanin stained waters, likely with leaf litter and driftwood. Oak leaves, driftwood and dense planting with allow this fish to feel safe during the day, with planting also offering diffusion of light. Sand is a requirement for keeping Hara catfish, preferably softer sands such as Silica sand and Black Iron sand.

Hara catfish are quite shy fish and it's best not to expect to see them out much during the day - perhaps they may be spotted sitting on leaves, but usually they are hidden away. It is possible to "train" them to eat not long before lights are off, so you get to see them forage around for food. Due to being both nocturnal and shy, it's best to keep these fish as the only bottom dweller in the tank, and to feed enough (before or after the lights turn off) so that any top dwelling fish don't out-compete them for food. Hara cats are omnivorous but appreciate a diet of predominantly live foods, however they may take algae wafers or fresh vegetables to make up for vegetable matter.

Hara cats are compatible with many Nano fish, but an important thing to note is that they prefer cooler waters, so aren't suitable for living with Bettas, for example. Well oxygenated water is a must, so live plants and surface movement are good to keep up the oxygen levels. When out and about, these fish provide a lot of entertainment as they rummage around for food - they're also pretty strange to look at!

Some Basic Facts:

Minimum Tank Size: 38 Litres Compatibility: Peaceful, Shy
Maximum Size: 3.0-3.5cm Ideal Temperature: 20-25 Degrees C
Ideal pH: 7.0-8.3 Ideal Hardness: Soft-Medium Water
Diet: Omnivorous Reproduction: Spawns on vegetation such as moss


55L and Over:


Small Shoalers


Ember tetra Hyphessobrycon amandae

Above: Ember Tetras (Hyphessobrycon amandae)


There are a variety of small shoaling top dwelling species available for smaller aquariums. Their care tends to be similar, often needing: low to moderate flow, dense planting, low lighting, soft water and large numbers. Their temperature ranges can vary depending on their locality, as some may come from shallow streams or cooler lakes and deeper waters. A lot of these species are shy and easily out competed for food, meaning they need a good sized shoal and peaceful tankmates. Many of these species are also jumpers, and may require a tight fitting lid. These fish tend to be smaller Danios, Rasbora and Tetras coming from South America and Southeast Asia but there are many different shoaling fish around the world!

Some species may include (in no particular order):

Emerald Eye Rasbora (Brevibora dosriocellata), Chilli Rasbora (Boraras brigittae), Dwarf Rasbora (Boraras maculatus), Celestial Pearl Danio or Galaxy Rasbora (Celestichthys or Microrasbora erythromicron), Clown Rasbora (Rasbora kalochroma), Sawbwa Rasbora or Asian Rummynose Tetra (Sawbwa resplendens), Lambchop Rasbora (Trigonostigma espei), Glowlight Rasbora or Slender Wedge Rasbora (Trigonostigma hengeli), Harlequin Rasbora (Trigonostigma heteromorpha), Neon Blue Rasbora (Sundadanio axelrodi), Dwarf Danio (Danio nigrofasciatus), Ember Tetra (Hyphessobrycon amandae), Green Neon Tetra (Paracheirodon simulans)

*Bolded means readily available/common


Honey Gourami


Honey Gourami Female Gold

Above: Honey Gourami (Trichogaster chuna Female 'gold')


Honey Gourami (Trichogaster chuna) are sweet and sensitive little fish belonging to the Anabantoid (Gourami) family, meaning like Betta fish they use a Labyrinth organ to take in air and are also Bubble-nesters. However, unlike Betta fish, the male and female Honey Gourami can live together and the best ratio tends to be 1 Male to 2 Females. Also coming from areas with low flow and tannin-stained waters, it's recommended to keep them in a soft water setup with leaf litter, driftwood and peat. These guys will appreciate dense planting and plenty of hiding places, which will also help to reduce stress on the females when the male is in breeding condition.

Provided water conditions are pristine, Honey Gourami are fairly easy fish to keep and are compatible with a range of tankmates. Due to being prone to infection when wounded, tank mates need to not be fin nippers, boisterous fish or large fish, but other than those requirements the Honey Gourami can live with many different fish. Recommended tankmates are small, peaceful shoalers such as Rasbora or small Tetras, along with quiet bottom dwellers such as Hara Catfish and Otocinclus species. The male and female Honey Gourami can be a bit hard to tell apart, but they do display sexual dimorphism when in good conditions. It can change based on their colour strain, but males tend to develop black colouration along their anal fin and abdomen, (like the fish above) and the dorsal fin may go a brighter yellow-blue colour. The males tend to be slimmer in the body and more streamlined compared to females which are rounder in both the abdomen and body shape. Females develop a black lateral line, but males may also show this line when stressed. Because males lose their colour and can appear female under stress, it can be tricky to sex Honey Gourami in store so it is not uncommon to accidentally come home with two males. Males also tend to display more territorial behaviours, especially when given the chance to nest (eg in a low-flow setup).

Being omnivorous, Honey Gourami accept a variety of food and are not particularly fussy eaters. However, it's recommended to feed them a good diet of live foods as they often predate on small insects in the wild.

Honey Gourami are excellent "feature fish" for many tanks, and they will gladly swim up to the glass to greet you (and, obviously, beg you for food). You can read about all kinds of Gourami and their setup here.

Some Basic Facts:

Minimum Tank Size: 55 Litres Compatibility: Peaceful, Shy
Maximum Size: 4-5cm Ideal Temperature: 23-28 Degrees C
Ideal pH: 6.0-7.5 Ideal Hardness: Very soft-Medium water
Diet: Omnivorous Reproduction: Bubble-nester



otocinclus oto catfish

Above: Otocinclus sp.


Otocinclus ("Otos") come in a variety of species in NZ as there are nine species allowed for import, however the more common species are Otocinclus affinis and Otocinclus vittatus, although the care for them all tends to be very similar. There are very few breeders of Otos in New Zealand and because of this almost all available in pet stores are Wild Caught from South America and tend to be very sensitive fish. Otocinclus are well known for being prone to death during acclimatization (the first 2 weeks of being in the tank), due to this and their sensitive nature these fish are typically not recommended for beginners. Despite their difficulties, Otos are fantastic fish to watch and show many interesting behaviours.

Otocinclus come from slow to moderate flowing acidic streams and are often found on mats of dense vegetation. Because of this, Otos will thrive in a setup of dense planting and broad leafed plants such as Java Fern, Anubias or Hygrophila corymbosa and may also appreciate leaf litter and the tannins they provide. Although they spend little time on the substrate, due to being scaleless Otos may prefer a sandy substrate. Otocinclus are shoaling in nature and definitely prefer to have conspecifics present, meaning that groups of 5 or more are necessary to prevent stress. These fish may often in the wild be found in the hundreds, so on their own they are prone to becoming stressed. They are very sensitive to water conditions, so Nitrates must be kept below 20, below 10 if possible.

Otocinclus are known for their ability to eat Brown Diatoms ("brown algae") in aquariums and are often recommended for this purpose, however it's worth noting that some struggle to convert to prepared foods and it's even recommended to have a good supply of Brown Diatoms available in case you are unlucky to have a fussy eater. Some soft vegetables such as Zucchini or blanched Spinach may be appreciated and help to provide a good diet for the Oto. Otos are very peaceful, but due to their shy nature and fussy diet it's best to keep other shy tankmates and to avoid other bottom dwellers to prevent them being out competed for food.

Some Basic Facts:

Minimum Tank Size: 55 Litres Compatibility: Peaceful, Shy
Maximum Size: 3-4cm Ideal Temperature: 21-26 Degrees C
Ideal pH: 5.5-7.5 Ideal Hardness: Very soft
Diet: Vegetarian Reproduction: Unknown, possibly Egg-scatterers


In Conclusion

Nano tanks are both a challenge and a fun journey to set up and maintain. They are practical for many hobbyists due to their size and despite any extra care they're enjoyable to keep. There are hundreds of thousands of fish around the world and despite our import list only being a fraction of that, there are still many options available and this grows as more species are discovered and become readily captive bred. The amount of options available today are higher than that of 10 years ago, and hopefully in another 10 years there are even more fish available!

We thank SeriouslyFish and FishBase for reliable information such as the basic facts used in this article.

A tropical fish

Here you will find our glossary of words, acronyms and phrases that you may see used on the website and among other Fishkeepers. Got a word you're unsure of and want added to the list? Let us know in the comments below!


Navigation: Feel free to use the Table of Contents below, or use Control+F to type in the word you're looking for.


Table of Contents:


Common/Basic Terms:

Cycle: The “cycle” is the term used for the Nitrification cycle which occurs in the aquarium’s filter. It is where the filter bacteria converts Ammonia into Nitrite into Nitrate. Nitrate is the final product, unless water changes are done, the tank is planted or a “denitrification” method is used.

Bioload: The amount of waste a fish makes.

Conspecific: Fish and other organisms from the same species.

"The List": Typically refers to the Biosecurity List of Fish and Invertebrate species allowed to be imported into New Zealand. The List can be seen here (warning: large file size)

Binomial Name: Also sometimes called a Latin name or Scientific name, the binomial name contains the genus and species of an individual fish or living organism. For example, Hypancistrus zebra is the binomial name given fro the Zebra Pleco. Binomial names are typically a more accurate identification of a fish, as common names are often used for several different species. The binomial name of an organism is typically written in italics and the genus is capitalized, whilst the species is written in lower-case. A binomial name may sometimes be written as "Hypancistrus zebra Isbrücker & Nijssen, 1991" - the Isbrücker & Nijssen indicating the individuals who first published the description of the species,  and 1991 indicating the date in which it was first published.

Common Name: A common name is the name used to easily represent a species without the requirement of remembering the Binomial name. For example, Zebra Pleco would be the typical common name used for the species Hypancistrus zebra. Unfortunately, using common names is not always an accurate way to identify species, as a single species may be given several common names and a single common name may be used for several different species. For example, Trichogaster chuna may be given the names "Golden Honey Gourami", "Honey Gourami", "Sunset Red Gourami" and so-forth - all of these common names may also be used for Trichogaster labiosa and sometimes Trichogaster lalia

L-Number: The L-Number is a number given to members of the Loricariidae family (commonly called Plecos) by fishkeepers in order to identify them. These names can often be extremely useful for individuals that don't yet have a designated species, as the number (such as L046) is less ambiguous than common names (such as Zebra Pleco) which are often used for multiple species of fish. It's worth noting that multiple L-Numbers can be given to a single species based on natural variations from collection points. A similar classification also has the prefix LDA.



Water Chemistry

NH3: Ammonia, which is needed for the cycle process to start.

NO2-: Nitrite, the first product of the cycle, converted from Ammonia.

NO3-: Nitrate, the final product of the cycle, converted from Nitrite.

Nitrification: The cycle that turns Ammonia into Nitrite, and then Nitrite into Nitrate. Typically performed by aerobic bacteria, such as those that live in filters.

Denitrification: The "completion" of the nitrification cycle, producing dinitrogen (N2) gas. Denitrifying bacteria are typically anaerobic and may live in areas such as deep in the substrate. Denitrification is not necessary and may even be avoided by some, with planting and water changes being the preferred methods for reducing Nitrates.

Anaerobic Bacteria: Anaerobic bacteria are those that thrive in areas with little to no oxygen concentration.

Aerobic Bacteria: Aerobic bacteria are those that thrive in areas of moderate or high oxygen concentration.

pH: The measurement of the Acidity or Alkalinity (not to be confused with KH alkalinity) of the water. Measures the presence of Hydroxide (OH-) and Hydrogen (H+) ions in the water.

Acidic: A pH under 7.0. Shows up as Red-Yellow-Lime with Universal Indicator (a pH test kit)

Alkaline: A pH above 7.0, also called "Basic". Shows up as Cyan-Blue-Purple with Universal Indicator

Neutral: A pH of 7.0. Shows up as Green with Universal Indicator

dGH: Degrees of General Hardness, the measure of Calcium and Magnesium (2+) ions in the water. Is typically greater than the dKH.

dKH: Degrees of Carbonate Hardness or Alkalinity (different to the water being Alkaline), the measure of the Carbonate and Bicarbonate anions in the water. Determines the "buffering capacity" of the pH, and has an affect on the pH of your water. For example, a low KH typically means acidic water, and a high KH typically means alkaline water.

Very Soft: 0-4 dGH / 0 - 70 ppm

Soft: 4-8 dGH / 70 - 140 ppm

Medium Hardness: 8-12 dGH / 140 - 210 ppm

Fairly Hard: 12-20 dGH / 210 - 350 ppm

Hard: 20-30 dGH / 250 - 530 ppm

Very Hard: 30+ dGH / 530+ ppm

Cold Water: These three terms can differ from person-to-person, but cold water tends to mean under 18° Celsius

Subtropical: Waters that sit between 18° Celsius to 24° Celsius

Tropical: Waters that sit between 25° Celsius to 32° Celsius



General Acronyms:

LFS: Local Fish Store

LPS: Local Pet Store

WC: Water Change or Wild Caught depending on the context.

CB: Captive bred

BB: Beneficial Bacteria

MPI: The Ministry for Primary Industries. MPI primarily create and enforce the legislation around the importation and keeping of 'ornamental' fishes (fish used in Aquaria), plants and invertebrates in New Zealand. See their website here.

IHS: Import Health Standard - this usually refers to legislation created and maintained by MPI in regards to the importation of 'ornamental' fishes, plants and invertebrates in New Zealand. For example, the IHS for Importing Ornamental Fish and Marine Invertebrates can be found here.

MTS: Depending on the context, this can mean Multiple Tank Syndrome (referring to the desire to get more tanks!) or Malaysian Trumpet Snail.

HITH: Hole in the Head Disease

IPs: Internal Parasites

Sp.: The abbreviated form of species. May be used after an undefined/unknown species of fish where the genus is known (Eg. Apistogramma sp.).

Spp.: The plural form of species. May be used to refer to several different species of fish within a genus (Eg. Apistogramma spp.).

Var.: Abbreviation for variety. Used to give a variety of a specific species (Eg. Hygrophila polysperma var. 'Sunset')

Cf.: Compare or Confer, may be used when the species is undescribed or unknown. This means it may be the species given but may be different (Eg. Ancistrus cf. cirrhosus).



Basic Fish Anatomy

basic fish anatomy 01

Dorsal Fin: The dorsal fin is an unpaired fin located along the top-back of the fish and may be short and sharp, or may continue past the dorsal fin (particularly in captive long-finned varieties of fish). The main role of the dorsal fin is to stabilize the fish and maintain its balance. The dorsal fin is present on the majority of fish, however some captive-bred mutations may prevent the dorsal fin from being present. 

Adipose Fin: The adipose fin is an unpaired fin and sits behind the dorsal fin on the top-back of the fish. Although it does appear to have a minor effect on swimming[1], the true "purpose" of the adipose fin is largely unknown. The adipose fin is not present in all fish, however it tends to be present on many Tetra species and some Catfish (Siluriformes family) species.

Caudal Fin: The caudal fin sits at the rear end of the fish and is also known as the tail fin. The role of the caudal fin is to control movement speed, and is present on the vast majority (if not all) fish. Caudal fins have been bred in captivity to produce large, flowing finnage, which may affect speed. This fin is typically unpaired, however a double dorsal fin may be present on some captive-bred varieties of fish such as 'fancy' goldfish.

Caudal Peduncle (not pictured): The caudal peduncle is where the caudal fin and body meet.

Anal Fin: The anal fin is present below the abdomen and, like the dorsal fin, the anal fin is used for stabilization. This fin is typically unpaired and present on the majority of fish, however some fish such as captive-bred varieties of 'fancy' goldfish may have double anal fins (along with extended finnage). 

Ventral/Pelvic Fin: The ventral fins are paired fins that sit below the abdomen and in front of the anal fin. The purpose of the anal fins is to control vertical and horizontal movement. These fins may be small and not particularly visible, or may be long and thin such as on fish such as Gourami (Osphronemidae family) and Angelfish (Pterophyllum genus) and may be used in a behaviour described as appearing to be "feelers".

Pectoral Fin: The pectoral fins are paired fins that sit on the sides of the fish behind the operculum and around the lateral line. The pectoral fins may be used for horizontal movement, balance and slowing of their movement speed.

Operculum: The operculum, also known as the gill cover, is a large bony flap used to protect the sensitive gills of the fish and aids in the flow of water for respiration.

Gills (not pictured): The gills consist of very thin, folded tissue with a high surface area to provide the efficient contact of water to blood necessary for respiration. The gills may be prone to parasites such as Gill Flukes and White Spot (also known as Ich, Ichthyophthirius multifiliis) and are also very sensitive to Ammonia.

Labyrinth Organ (not pictured): The labyrinth organ is a specialized organ used for respiration in some fish, particularly those in the suborder Anabantoidei (this includes the gourami and betta fish). This organ allows the fish to gulp and use air for respiration, which may aid in their ability to survive out of water for short periods of time. The labyrinth organ is not present when hatched, and develops as the fish grows.

Swim Bladder (not pictured): Also called an air bladder or gas bladder, is an organ present inside around the top of the fish which typically contains two sacs of air (although some species may only have one sac). This organ is necessary for buoyancy and vertical stability. Injury, infection or deformation of the swim bladder may cause a fish to sit at the top or bottom of the tank at an unusual angle.

Lateral Line (not pictured): The lateral line is a row of sensory organs that play a vital role in detecting water movements, electrical currents, pressure and vibration and helps with understanding a fish's surroundings. 



Fish Behaviour:

Flashing: A fish quickly moving against an object and "itching". Can be a sign of stress or disease (specifically external parasites), can also be harmless.


Breeding Terms:

Gravid: Applies to fish that are egg layers (not livebearers), meaning full of eggs

Ovipositor: Often referred to as an “egg spot”, the white spot at the bottom of a female fighter.

Spawn: The release of eggs from fish

Mouthbrooder: A fish that incubates and holds its eggs in the mouth. Many Cichlid species for example are mouthbrooders. Male fish that incubate their eggs are paternal mouthbrooders, female fish that incubate their eggs are maternal mouthbrooders.

Bubble-Nester: A fish that places and incubates its eggs in a nest of bubbles constructed by the fish. The most well known bubble-nesters are the males among certain Gourami species (Osphronemidae family) to construct bubble-nests, however Hoplo species (Megalechis thoracata) also reproduce via this method. Bubble-nests may be produced regardless of whether fish of the opposite sex are present.

Free-Swimming: Fry are called "free-swimming" when they become capable of swimming around the tank on their own without any assistance from the parent fish.

Line-Bred: This means that the fish has been specifically bred back to family members in order to assure a certain trait (whether this is visual, health, behaviour and so-forth) is carried down to the offspring. Line-breeding is common practice however it may result in unintentional deformities or health issues if done for too long. Different species of animals may have different "tolerance" to line-breeding or inbreeding.

Breeds-True: Also known as purebred or true-breeding, this means a pair in which the genetics of a certain trait are known and will always produce offspring with the same traits as the parents. To get parents that breed-true may require several generations of line-breeding, particularly if the trait that is being bred for is a dominant one.

Hereditary: A trait that is hereditary is a genetic trait that may be passed down to offspring. For example, Albinism is a hereditary trait.

Albino: A mutation that causes the absence of melanin pigment or colouration. Albinism is hereditary and passed down through recessive genes, and is primarily told apart from leucism due to the eyes also lacking pigment (causing a red colouration) - the body may also be tinted slightly yellow in comparison. Albino animals typically do not survive in the wild, but may be selected for in captivity.

Leucistic: A mutation that causes the absence of pigments or colouration. Leucism is hereditary and passed down through recessive genes, and is primarily told apart from albinism due to the regular colouration of the eyes. Leucistic animals typically do not survive in the wild, but may be selected for in captivity.

Allele: A form of a gene. Animals carry two alleles for each gene. Alleles may be recessive or dominant and are given an abbreviated form that is capitalized to indicate a dominant allele, and is written in lower-case to indicate a recessive allele. For example, if a was given as the abbreviation for the albino gene, a normal (non-albino) fish may be shown as AA or Aa, whilst an albino fish may be shown as aa.

Gene: The coding for a specific hereditary trait in a living organism. Genes may be complex and may interact with each other (with little visible effect), or they may have a single clearly visible effect. Albinism is an example of a variety of the gene that codes for pigment production.

Heterozygous: Hetero = different. This means that the fish is carrying two different alleles for a specific genetic trait. For example, a fish heterozygous for albinism may be shown as Aa, meaning it has one dominant and one recessive allele. 

Recessive: A recessive characteristic requires two alleles for a genetic trait in order to be visible. Breeding two fish with a recessive characteristic will result in all offspring showing the same phenotype as the parents, however both fish with a dominant characteristic would have to carry a recessive allele in order to produce offspring with the recessive characteristic. Breeding a fish that is homoyzygous for a recessive trait and a fish that is heterozygous for a dominant trait may result in 50% of the offspring appearing as one parent, and 50% of the offspring appearing as the other. for A fish showing a recessive characteristic must be homozygous and is represented with two lower-case abbreviations (Eg. an albino fish may be shown as aa). 

Dominant: A dominant characteristic means only one allele is required for a genetic trait in order to be visible. Breeding two fish homozygous for a dominant allele will result in all offspring being the same phenotype as the parents, however breeding two fish heterozygous for a dominant allele may result in 25% of the offspring resulting in a different phenotype from the parents. Breeding one a heterozygous fish with a fish that is homozygous for the dominant alleles will result in all of the offspring being the same phenotype as the parents.

Co-Dominant: Some genetic traits are not fully dominant. A co-dominant trait will be expressed when the fish is heterozygous for a specific gene and both mutations express equally. A common example of a co-dominant trait may be a calico form.

Incomplete Dominance: Like co-dominance, a trait with incomplete dominance is one where neither allele is fully dominant. A trait with incomplete dominance will be expressed when the fish is heterozygous for a specific gene. Unlike the calico-type appearance of co-dominance, a trait with incomplete dominance will look like a "mixed" form of both traits. For example, a white fish mated with a red fish that produces pink coloured offspring may be a case of incomplete dominance.

Phenotype: The expressed or visually apparent characteristic. The genetics of the fish do not have to be known in order for the phenotype to be known - for example, a fish may have a phenotype of albino or non-albino. A phenotype may have multiple possible genotypes.

Genotype: The known genetics of the fish. For example, a non-albino fish may have genotype of Aa or AA, whilst an albino fish may have a genotype of aa (if a is the abbreviation given for the albino gene). 



Planting Terms:

Emersed: Growth of plants with only the roots in the water. The rest of the plant body is grown outside of the water.

Submerged: Growth of a plant entirely submerged in the water, only "true aquatic" plants may be grown like this, as other plants will rot under these conditions.

Riparium: The use of Emersed plants outside of the tank water. May have reduced water level, allowing for plant growth to be contained within the tank.

Paludarium: A tank set up using terrestrial elements (land) and water. The water level may only be around 20% of the tank's height, and plants are often grown Emersed. Typically used for Amphibians, but large tanks may be used for fish.

Macro: Macro nutrients, often called NPK, are Nitrates (in the form of Nitrate, Nitrite or Ammonia), Phosphorous and Potassium.

Micro: Micro nutrients are often also called Trace Elements. These may include Iron, Boron, Calcium, Copper, Manganese, Cobalt, Zinc, Molybdenum and various other elements.

NPK: Nitrogen, Phosphorous and Potassium, considered to be Macro nutrients for the planted tank.

Cultivar: A variety of plant selected for through captive breeding.




Aufwuchs: German for "surface growth" - A name given to the micro-organisms that grow on surfaces such as rocks and plants. Commonly found aufwuchs may include algae, diatoms, annelid worms and other small aquatic invertebrates. Some fish such as certain African Cichlids or Plecostomus have specially adapted mouths for rasping on aufwuches.



Acronyms for Fish and Plant Species

BGK: Black Ghost Knifefish

DPF: Dwarf Puffer Fish

RTS: Red Tailed Shark

RTL: Red Tiger Lotus

GSP: Green Spotted Puffer

GBA: Golden Black Eyed Ancistrus



[1] https://thefisheriesblog.com/2013/05/28/the-adipose-fin-old-mysteries-with-new-answers/


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Table of contents:

Water Quality Issues

How do I?

Can I use this in my tank?

Fish Specific Questions

Food Questions

Fish Health

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