How many fish can I have?
There are a few formulas that can help you figure out how many fish a specific size aquarium can accommodate, but there is no hard and fast rule. The amount of fish will be determined by a variety of variables, the most significant of which are:
a) Size and kind of fish – While bigger fish obviously need more space than smaller fish, the type of fish is also significant. Some cichlids, for example, create more waste than other fish of comparable size and are territorial, requiring more area per fish. In estimating the amount of space needed, a fish’s body weight is more essential than its length, since body weight grows exponentially with length. As a result, a big stocky fish requires more water per centimeter/inch of body length than a long and thin fish.
b) Filtration – the better the filtration, the more fish you can keep in your aquarium, up to a point. The most significant aspect here is biological filtration. (For further information, read our filter information pages.)
c) Aquarium size and surface area – While water volume is crucial, keep in mind that gas exchange occurs at the aquarium’s surface, therefore surface area may be a limiting factor in determining the capacity of particular aquariums. Where there is excellent filtration and aeration, surface area is less critical.
Where there is excellent filtration, a basic guideline for the quantity of fish is to allow around 1 litre of water per cm of fish. Allow at least 2 litres per centimetre for small to medium-sized goldfish and cichlids, or when filtration and/or surface area may be limited. Allow extra water (3-4 l per centimetre) when the fish get bigger or become territorial.
The ability to judge the amount of fish a tank can house comes with practise. However, there are several techniques that may be useful.
When stocking a new tank, it is usually a good idea to introduce fish gradually. With each new fish you introduce, keep an eye out for indicators of stress (see here), both in the new and old fish. If the fish seem agitated, or if illness hits, you have most likely reached (or maybe beyond) the tank’s capacity.
Testing your water may also assist you identify whether your tank’s capacity has been reached. Check the pH of your water on a regular basis. You may safely add extra fish if this remains at or near the pH of your source water (or around neutral). If it dips fast, it is a solid indicator that there are too many fish in the tank or that the fish are too big for the tank. You may also keep an eye on the nitrate level in your tank. You may safely add additional fish if this remains at or near 0 (with no ammonia or nitrite). If it climbs significantly, your tank is most likely congested.
If you notice that everytime you add a new fish, an older fish dies, this is another indication that the maximum capacity has been reached; nevertheless, it is preferable to discover this through less damaging techniques if feasible!
What fish are compatible with each other?
Coldwater has a restricted number of species, most of which are suitable. Goldfish can grow big enough to consume tiny fish (such as danios and white clouds), but they are not violent and will only eat fish that they can readily swallow. As a result, bigger goldfish may be mixed with smaller goldfish, as well as any other fish larger than the gape of their jaws. Some coldwater fish are vicious. Giant danios and rosey barbs are fast swimmers that can nibble fins. They should be maintained exclusively in bigger tanks with other rapid swimming tank mates (eg comet goldfish, danios, but not fancy goldfish or fantails). Paradise fish are territorial and may be hostile, especially against one another, however they can be combined with fast swimming fish in a bigger tank. The majority of Australian coldwater indigenous are huge and aggressive, and they do not mingle with other species, although there are a few exceptions. See our fish species guide for more details.
Because there are literally hundreds of tropical species available, providing compatibility information on every potential combination of fish is difficult. There are, nevertheless, certain broad guidelines.
Community fish are fish that are calm and do not get too huge. Most community fish are friendly with one another; however, extremely tiny fish (such as neons) should not be mixed with bigger community fish (such as angelfish and gouramis), which may mistake them for food. Stick to a variety of little and medium fish, or one medium and bigger fish.
Fish that do not mix well do so for a variety of reasons.
For starters, they may become extremely enormous, and even if they are peaceful, most larger fish would devour little fish if given the opportunity. Mix these fish only with other huge species in a tank with enough space.
Second, they may be predatory and like to devour other fish. A predatory fish may not be aggressive, i.e. it may merely consume smaller fish that it can swallow whole, however many predators have unusually wide jaws for exactly this reason! Again, only combine them with fish that are too huge to consume. Some fish are predatory and aggressive, meaning they will attack and kill fish their own size or bigger for food. These fish can only be kept with fish that are either too swift to catch or can protect themselves.
Other fish are territorial, which means they will choose a location in the tank to protect from other fish. Some (for example, red tail sharks and rainbow sharks) achieve this by scaring other fish away, although typically without inflicting any serious harm. These may coexist in a communal tank, but not with fish that move slowly, are placid, or are easily stressed. Some fish (for example, many cichlids) defend their territories aggressively, and these should be combined with other fish of a similar temperament in a tank big enough for each to create its own zone.
Some fish are incompatible because they are timid, difficult feeders who might be overwhelmed by the regular raucous activity of communal fish. Discus are an excellent example. These fish should only be mated with tiny, peaceful species.
Finally, certain fish are incompatible because the water conditions they need are incompatible with those of other species. These are mostly brackish species that need alkaline water, preferably with salt added.
Look up the species you’re interested in in our species guide for additional information on fish compatibility.
Will my fish breed in the Aquarium?
The answer is usually no, although there are certain exceptions. Most fish are egglayers and will not spawn in a tank with many other species. Even if the water quality is acceptable and the fish reproduce, the small eggs are generally eaten rapidly in a communal tank. However, livebearing species (platies, mollies, swordtails, and guppies) are prolific breeders who are unaffected by the presence of other species.
Rather of laying eggs, these animals give birth to live young after the female is internally fertilised by the male. Although they can swim freely and consume finely crushed flake food, livebearer juveniles are quite tiny and are often eaten in a communal tank. If you wish to rear the young, you’ll need to either relocate them to a separate tank, separate them with a breeding trap or net breeder in the main tank, or give them with plenty of protection, such as plenty of plants to hide in.
Many cichlids may reproduce in the presence of other species in the aquarium. They will only breed if you have a mating pair (cichlids will choose mates and pair off; merely having a male and female in a tank does not ensure breeding) and they are content with the water conditions. Cichlids lay eggs, but instead of spreading them and abandoning them, they will deposit them in a secure spot (for example, on a rock or in a cave) and protect them. Some species may even brood the eggs in their mouth. If the cichlids are excellent parents and there aren’t too many other fish in the tank, they may be able to raise the young on their own. However, if the parents are agitated by the presence of other fish, or if they are plain bad parents, they will devour or leave their children or eggs. Even with the assistance of their parents, baby fish often do not have enough food and starve. For these reasons, it is advisable to nurture the young in a separate tank, either with or without their parents.
Other varieties of fish may reproduce in a communal tank, as previously stated, although this is quite unusual. If your fish do lay eggs, it is a solid indicator that they are content! Eggs are usually eaten extremely rapidly, so you’ll need a separate tank if you wish to breed the fish.
How can I sex my fish?
Some fish exhibit severe sexual differences, with males and females seeming to be distinct species! Some fish, on the other hand, exhibit no visible signs of sex. There are minor indicators that can be used to sex the fish in many species, but no rule applies to all species.
Some broad guidelines (with several exceptions) are as follows:
Male livebearers have gonopodiums, which are rod-shaped anal fins rather than fan-shaped anal fins. Females have an anal fin that is fan-shaped. Guppies, mollies, swordtails, and platies are examples of livebearers.
Males of numerous species, including many barbs and danios, guppies, and certain tetras, are smaller and brighter than females. Females are often plumper.
Males of several species, such as gouramis and some cichlids, have longer fins, notably the dorsal and/or anal fins. Some tetras and some cichlids have caudal (tail) fin extensions.
Males and females of certain cichlids have different colours or have distinct patterns. Only the males are colourful in others, while the females are drab or grey.
What should I feed my fish?
There are a variety of diets available to feed your fish, including flakes, pellets, frozen, and live feeds. It is essential that you choose a meal that meets the needs of the fish you want to maintain.
A decent quality flake or pellet meal will give a balanced diet with all required vitamins and minerals for most animals. There is no need to switch brands as long as you choose a high-quality flake or pellet food. It depends on the fish whether you give flakes, pellets, or both. However, it is undoubtedly useful to supplement your fish’s diet with supplemental flakes or pellets and frozen meals. Live and frozen meals are the closest similar to what fish consume in their native environments, and feeding them may make your fish more vivid, colourful, and likely to spawn. They may, however, be deficient in certain critical vitamins and minerals, which a prepared dish will give. Frozen meals are preferred over live foods for a variety of reasons, which are listed below.
- FLAKES AND PELLETS
Flakes are intended to float at first before progressively sinking into the water. This is because certain fish like to eat at the tank’s top (for example, gouramis and danios), while others prefer to feed from the intermediate layers (tetras and barbs), and still others feed from the bottom (eg catfish). When you have a small community of fish, flakes are the ideal option as a staple diet, particularly if you have a mix of species that swim at all water levels in the tank or mostly at the top and middle levels. Flakes may not be enough to fulfil the demands of bigger fish, and the quantity reaching the tank bottom may be insufficient, causing catfish to miss out.
Pellets are also more concentrated and cost-effective than flakes.
Pellets are offered in both floating and sinking varieties. Floating pellets are ideal for bigger fish (such as cichlids), who like to eat from the surface. These are available in a variety of sizes, allowing you to choose one that is appropriate for your fish. Catfish like sinking pellets. Sinking wafers with a high concentration of spirulina, a very nutritious alga, are also available for algae eaters. Some pellets include both floating and sinking grains in a single container. These are suitable for community tanks with somewhat bigger fish, or if bottom feeders (e.g. catfish) as well as middle and top level feeders are present, for cichlids where not all fish eat at the top, and for larger goldfish that feed at all levels in the tank.
Pellets are not appropriate for all fish since some cannot fit them into their mouths. Furthermore, since pellets are more concentrated, they are simpler to overfeed than flakes. Feeding pellets should be done with care, particularly if you are new to raising fish.
Press-on feeding pills are another option. These may be pressed against the tank’s glass at any level and release little food particles.
- LIVE AND FROZEN FOODS
There are several varieties of live and frozen meals available. Brine shrimp (also known as artemia) and black worms are the most prevalent live meals. Tubifex, daphnia, earthworms, white worms, mealworms, and other organisms may also be present.
Brineshrimp is a kind of little salt water shrimp. Blackworms are freshwater aquatic worms that are lengthy but exceedingly thin. While some live foods may be highly healthy, we suggest using them with care and always choosing frozen over live. This is due to a variety of factors, but two in particular. The first is nutrition: unless living foods are very fresh, most of their nutrients is lost, and if the live food has died off, it will rot and may even generate poisonous by-products. The second factor is sickness. Live foods may transmit illness, although frozen foods can not. In most circumstances, frozen goods are also less expensive than fresh meals. Fish that consume live meals may become finicky and aggressive.
Other live meals to consider include: Daphnia, or water fleas, which are a little crustacean that are very nutritious. They are, however, difficult to cultivate and very seasonal, so they may be tough to get.
Earthworms are a good source of protein for big fish, particularly predatory species.
White worms are tiny burrowing worms. These are a great treat for little fish.
Meal worms are the larval stage of a beetle, not a worm. Because of their relatively high fat content, they provide an excellent occasional treat for predatory animals.
You may be able to gather additional living foods on your own, but there is a danger of disease transmission if you collect insects and other organisms from natural streams. Any flying insects (including flies) that have not been treated with flyspray are safe to feed to your fish. Earthworms from the garden and mosquito larvae from rainwater tanks may also be collected.
Some live foods, such as brineshrimp and daphnia, are also available in frozen form. Plankton, mysis shrimp, krill, bloodworms, beefheart, vegetable diets, and other mixtures to fit individual diets or community tanks with a variety of species are also available frozen.
Bloodworms are really midge larvae, not worms (similar to mosquito larvae). They have a similar nutritional profile as blackworms and, although an excellent treat, should not be given too often, especially to rift lake cichlids and vegetarian fish.
Plankton, mysis shrimp, and krill are salt water shrimps with nutrition comparable to brine shrimp but a greater protein and fat content. They are a fantastic complement to marine fish feasts since they are suitable for the diets of medium and bigger fish. Krill is very beneficial to predatory fish. These feeds are ideal for rift lake cichlids since they are lower in fat than bloodworms and beefheart.
Beefheart is a kind of lean red meat. It contains a lot of protein and is an excellent supplement for predatory fish. It is often served with liver, which is likewise low in fat but abundant in vitamins and minerals. Non-predatory fish should not be fed a lot of meat since it might cause fatty liver degeneration.
Spirulina and other beneficial algaes are found in vegetable diets. They are an excellent complement for any sort of fish and are especially beneficial to herbivores.
Other frozen meals are made out of a variety of components, such as brineshrimp, worms, beefheart, and spirulina. These are appropriate as a complement to community tanks. Some include a combination of substances aimed towards a certain variety of fish (eg discus).
- CHOOSING THE RIGHT FOOD
Look at the nutritional information on the tin before selecting a flake or pellet food. Flakes and pellets are available to fulfil the demands of many types of fish.
You don’t need a high protein meal for goldfish (about 35% is adequate), and you should select one that is low in fat (around 5% – decent goldfish feeds will meet this criteria). If you want your goldfish to grow quicker or to produce the elaborate headgrowths of orandas and lionheads, offer a higher protein (35 – 45%) goldfish food or incorporate some tropical fish food in their diet. If you do this, be sure to supplement their diet with live or frozen food, preferably frozen brine shrimp or mysis shrimp, since a rich diet might lead to constipation and swim bladder issues. In any event, brine or mysis shrimps are a wonderful supplement for goldfish, and the naturally occurring pigments in these shrimp (especially brine shrimp) help bring out the goldfish’s rich red colour. Earthworms are another tasty food, particularly for bigger goldfish. Goldfish eat at various levels in the tank, and flakes or pellets are both acceptable. Flakes are often excellent for little goldfish, whereas pellets are preferable and more cost-effective for bigger goldfish.
Other coldwater species will live, but not flourish, on goldfish food. It is best to supplement their diet with a tropical flake or pellet food, as well as a variety of frozen foods.
Tropical fish have more stringent nutritional needs and need a higher protein diet (40% or more). Foods with a greater protein content are typically of better quality, but you need also evaluate the protein source. Look for meals that employ high-quality proteins like fish, shrimp, or krill, as well as algal meal, rather than inferior proteins like potato or soy meal. Brine shrimp, carotene (a natural colour enhancer), and spirulina are other excellent components (which boosts fishes immune systems and is also a colour enhancer).
Choose a flake or tiny pellet with a combination of floating and sinking varieties for a communal tank where fish eat at various levels. If you have catfish, you may want to add additional sinking pellets or algal wafers to ensure they don’t go hungry, or use a tiny granule diet (granules, like flakes, combine both floating and sinking components, but granules sink a bit quicker, giving your catfish more food). Frozen meals such as brine shrimp, bloodworms, daphnia and mysis shrimp, or community mixtures, as well as supplementary feeds such as brineshrimp and/or spirulina supplemented flakes or pellets, may be added to the diet of community fish. Press-on feeding pills are also a wonderful supplement; they are very nutritious, but if taken as a standard diet, they may be costly.
Cichlids are more active and predatory by nature, and their diet in the wild comprises more fat and animal protein. Cichlid meals often have a greater fat content (7-8%), which is good for these fish. Flakes or pellets are appropriate, with pellets preferred for bigger fish. Frozen brine shrimp, earth worms, meal worms, bloodworms, mysis shrimp, plankton, krill, and lean beef heart (or beef heart & liver) or supplementary flakes or pellets with a high amount of shrimp meal may supplement the diet of predominantly piscivorous animals.
Some species, particularly those from Lake Tanganyika, angelfish, and miniature cichlids, are not as predatory. Angelfish foods often include more vegetable matter and are acceptable for all of these species. Spirulina-enriched flakes or pellets, any of the frozen meals listed above (but not too much beef heart or meal worms), and frozen vegetable diets may also be used to enhance their diet. Marine diets are also appropriate.
Herbivores. Some fish feed mainly on plants (eg plant or algae eaters). Spirulina, in the form of flakes, pellets, wafers, press-on tablets, or frozen, will help these species. Brine shrimp, mysis shrimp, plankton, and daphnia are also excellent frozen feeds. Blanched lettuce leaves, peas, or zucchini may be used to provide more plant content.
How much should I feed them and how often?
You must exercise caution not to overfeed your fish. This is one of the most frequent errors made by beginner fishkeepers, and it may quickly lead to serious difficulties and fish fatalities. But, precisely, what is overfeeding?
Overfeeding refers to how much food is provided to the fish at one time rather than how often they are fed. Fish may be fed once, twice, three times, or even more times each day. It is advised that you feed your fish at least once a day, however a generally well-fed fish may go for a few days without food with no bad consequences. Feeding your fish more often implies that they will develop quicker, and waste products (such as nitrate) will accumulate in the aquarium more rapidly since the fish are consuming more food each day. If you have a tiny tank, especially one without a filter, you should only feed it once a day (or two very small feeds). It is normally ideal to feed the fish twice or three times each day in bigger, filtered aquariums, but you may feed them even more often if you choose (eg if you want them to grow faster). Feeding your fish more often throughout the day may also assist to divert them from nibbling on your water plants, although this does not always work.
However, as previously stated, the amount of food supplied at each meal is the most significant factor. While some basic principles specify the quantity of flakes or pellets per fish, this might be deceptive since flakes and pellets vary in size and food content. Give your fish the quantity of food they will eat in 2 – 3 minutes in small tanks with few fish, or in 4 – 5 minutes in bigger tanks with more fish. Because a fish’s stomach is just around the size of its eye, the quantity of food required is little. Begin by feeding much less than you believe the fish will consume. If they finish it in less than a minute, add a bit more until you have a good idea of the proper quantity. If, after 4 to 5 minutes, there are any food particles floating in the water or sitting on the bottom of the tank, then you have given them too much. Remove any surplus food using a net or syphon, and feed less the next time.