Ask the WWM Crew
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So you've got your aquarium and you've cycled it and you're raring to add some fishes! But which ones...? That's the tricky bit, because not all the fishes sold in aquarium shops will necessarily work well together in the same aquarium.
The size of the tank matters. Aquarists looking to set up their first tank should always buy a 20-gallon tank or larger. 10-gallon tanks are simply too small for easy fishkeeping. Because they contain so little water, they are subject to rapid fluctuations in water chemistry and water quality, and this can lead to the death of the fish. It is also more difficult to choose fish that will live happily in so small an aquarium. By all means use a 10-gallon tank to spawn a pair of dwarf cichlids or rear some livebearer fry, but as a community tank -- no thank you!
Should you get a tank that is bigger than 20-gallons? That's a judgment call. The bigger the aquarium, the easier it will be to maintain and stock. But it will also require a bigger investment in terms of filtration, lighting for plants, decorative materials and so on. When it comes to water changes, bigger tanks will also require proportionally more effort. As a general rule, inexperienced aquarists will find tanks in the 20-55 gallon range an ideal balance between stability, ease of maintenance and expense.
Without exception, the ideal situation is to establish your water chemistry fish, and then choose what fishes you want to add to the aquarium. You should never use water from a domestic water softener, the water chemistry that is produced by such devices is all wrong for keeping fish. Instead use plain tap water, treated with dechlorinator. If you have hard and basic water, don't bother keeping fish that only do well in soft and acidic conditions. Likewise if your water is soft and acidic, then keeping fish that need hard and basic water conditions is unlikely to work out well. In fact most aquarium fish are quite adaptable and will do well across a broad range of water chemistry values. Don't bother trying to adjust the water chemistry; doing so is a complicated business, and at this stage in your fishkeeping career you have enough to worry about already!
Community fish that need soft, acidic water conditions include (pH 6-7.5, 5-10 degrees dH):
Community fish that need hard, basic water conditions include (pH 7.5-8, 10+ degrees dH):
Community fish that will tolerate a broad range of conditions, provided extremes are avoided (pH 6-8, 5-20 degrees dH)
It goes without saying that all fishes do best when the water is clean and well filtered. But some fishes are especially sensitive to poor water quality, and for that reason shouldn't be purchases while you're still maturing your tank and learning the necessary fishkeeping skills. Leave these delicate species for 6-12 months down the line once you're comfortable you know what you're doing.
Even if you choose only the hardiest fish species, this still doesn't get you off the hook with regard to water quality. Cycle the tank using a fish-less method (there are many products on the market to do this, as well as DIY recipes using household ammonia). Once you're done, add the first fish and feed sparingly, keeping a regular check on pollution levels by measuring the nitrite concentration at least once a week. Perform regular water changes (25-50% per week) and make sure the filter is up to the job (a good baseline is a filter that provides 4 times the volume of the tank in turnover per hour).
Hardy community fish suitable for beginners include:
Delicate community fish beginners should avoid include:
Fish are not mindless automata; they have very specific social behaviours that they will attempt to express whether you'd like them to or not! In some cases, you have to accommodate their social needs if you want to see them at their best.
Schooling fish simply must be kept in groups of at least six specimens. If kept in too-small a group will become shy, nervous, and possibly aggressive towards their tankmates. Inexperience aquarists often choose fish like candies, wanting as much variety as possible. With schooling fish this can be a mistake! Schooling fish unquestionably look their best in groups, and the bigger the group, the better they look. When kept properly, they will show much better colours, and more importantly, they will stay in full view more of the time, so you can appreciate them fully.
Schooling community fish include:
Other fish are territorial and mustn't be overcrowded. Each specimen will want to have its own corner of the tank or its own cave, and if you force too many of them to share a space you are likely to end up with problems. Ideally, these sorts of fishes should be kept either on their own, in pairs, or in groups of one male per two or more females.
Territorial community fish include:
One of the most annoying behaviours among fish is fin-nipping. The biological causes for this behaviour are multiple and need not be gone into here. What is critical is that fin-nipping species should never be mixed with fish that are slow moving and/or have long fins. Gouramis, angelfish, fancy guppies, and Bettas are the usual victims of fin-nipping behaviours.
Known fin-nippers among otherwise good community fish include:
Community fish, by definition, don't normally try to eat one another. Livebearer fry and Corydoras eggs will of course end up being eaten, so if you want to breed these species you will need to isolate them. But in general anything labeled as a community fish should be non-predatory towards its tankmates. However, some species of community fish can and will eat very small tankmates, even though they are otherwise harmless. Avoid having extreme differences in size when stocking your tank; adult angelfish for example are more than capable of eating neon tetras.
Potentially predatory community fish include:
Fish swim at three distinct levels in the water column: the top, the middle, and the bottom. Fish that swim at the top tend to be streamlined and have upturned mouths. They typically feed on insects that have fallen onto the surface of the water. Midwater fish are sometimes streamlined and active swimmers, but many are more sedate preferring to hide among the aquatic plants. Many of these lurking fish are lunge predators, snapping at prey that gets into range. The bottom-dwelling fish have mouths that open downwards and many species are equipped with whiskers or barbels that help them find food in the mud. Some are herbivores, others carnivores.
When setting up your community, you want to have fishes swimming about at all levels. This will keep the aquarium looking busy but not cluttered. If all the fish are at the top of the tank or at the bottom it will look crowded, but if you spread the fish out, you will get a much better effect. Since the middle layer of the tank is effectively a bigger place than either the very bottom or the very top, you want to choose rather more midwater fish than bottom dwellers or surface fish. For example, if you were keeping Danios with lemon tetras and Corydoras catfish, you might choose to have six Danios at the top, twelve lemon tetras in the middle, and six Corydoras catfish at the bottom. This would give you a nice balance of similar-sized fish at different levels of the tank.
Small surface-dwelling community fish:
Small midwater community fish:
Small bottom-dwelling community fish:
While most aquarists quickly grasp that not all fish feed at the same level of the aquarium, inexperienced aquarists often don't understand that not all fish will eat the same food (i.e., flake food) and nor will they all eat the same time (i.e., during the day). Just as important is the fact that many fish are rather shy at feeding time. In the wild such fish often have very specific ways of obtaining food, perhaps winkling out small animals from the mud or hiding among plants to snap up things that swim by. While fine in the wild, in the confines of an aquarium these fish will lose out when forced to compete with boisterous fish that feed quickly.
So before buying any fish, make sure you know precisely what they will eat. Many of the small schooling fishes kept by aquarists are insect-eaters in the wild, and because their instinct is to snap at things that land on the surface of the water, they very quickly learn to take flake foods. The more popular catfish are opportunistic and eat anything that tastes nice; while that may be bugs and algae in the wild, in captivity they quickly switch to catfish pellets and algae wafers (plus some vegetable foods in the case of Plecs). Cichlids and gouramis tend to be adaptable and will sample most food items offered to them, and the commonly traded species can be expected to do well on flake foods and small pellets. Frozen bloodworms and live foods are very popular with most aquarium fish, but for these hearty eaters they are not at all essential.
More specialist fishes on the other hand may not take pellets or flake at all, and live or frozen foods will be essential. If you don't want to have to deal with that, don't buy fishes with specialised modes of feeding.
Fish that are easy to feed on flake and pellet foods include:
Fish that are will require special foods or careful feeding include:
Some fish are notorious for poor health. The reasons for this are various, but for the inexperienced fishkeeper none of that matters: the main thing is to avoid them! Community fish that so regularly exhibit health problems they should be avoided include:
Disruption to the plants and decor
Although this aspect of fish selection is often overlooked by inexperienced aquarists, it is very important in the long term: some fish will eat plants. While they might not do much harm while they're small, as they grow, they eat more plants. Often it isn't just the damage to the plants that's the problem, but that dead plant material drifts around the tank clogging up filters and overflows.
Notable plant-eating fish include:
Other fish don't directly eat plants but they will uproot them by digging. Cichlids are notorious for this, and it is very important you check whether or not a cichlid is a digging species before adding it to a planted aquarium. In general dwarf cichlids and angelfish are good additions to planted aquaria, but other species should be approached with caution unless you know better! Even in an unplanted aquarium digging fish can cause problems by undermining carefully arranged piles of rock or bogwood. In extreme situations, the fish can move so much sand or gravel that heavy objects can fall with enough force to crack glass. Always ensure heavy objects are securely arranged and if necessary use aquarium-grade silicone to fix them into place before adding the fish.
Digging fish include:
There are lots of excellent aquarium books aimed specifically at beginners. These will give you information on water chemistry and filtration topics as well as provide some ideas for livestock. The following titles are ones this author particularly likes, but there are many others.