Tetras are a group of fishes from the Characidae family, commonly called Characins (ka-re-sen), which are found throughout Africa and South America. The name 'Tetra' is used for many Characins but applies especially to the Hyphessobrycon, Paracheirodon, Megalamphodus, Moenkhausia, and Nematobrycon species. Virtually all Characins have a connection between the hearing organs and the swim bladder, called the 'Weber's apparatus' which allows the swimbladder to amplify sounds. Characins are also very adept at picking up chemical signals from the surrounding environment and from other fishes. Both these traits mean that the fish is very aware of, and sensitised to, changes in its environment. Under natural conditions the extra sensitivity allows the fish to become particularly good at forming shoals, finding food, and escaping danger. In the aquarium the same applies, but another result is that the fish are overly sensitive to vibrations and water quality fluctuations. In fact, it is quite common to see problems related to the fishes nervous system in shop sales tanks or when newly introduced into the aquarium. If you have ever seen a small Tetra or Characin slightly bent round and very rapidly 'spinning' out of control followed by a period of little movement, it is likely to be caused by some form of nervous system overload.

The relatives
As part of the Characin family, the Tetras are very closely related to some Characins that you would not normally associate with the humble Neon Tetra. The most notable of these is the Piranha group, which despite their partly undeserved bloodthirsty reputation, are incredibly similar to the smaller tetras. Both groups are shoaling fish, with a timid and skittish nature when kept alone or in small numbers, have highly developed senses, and are primarily carnivores. There are also many vegetarian relatives including the Silver Dollars, Distichodus sp., and Leporinus sp. and the more unusual oddities include the Hatchetfish, and Headstanders.

Water conditions
Although wild preferences do vary, the vast majority of tetras are found in well-oxygenated water, which is clear and running. Tetras do not cope very well with low oxygen conditions and so are rarely found in isolated pools, preferring either clear streams or the banks of larger rivers. Because they are easily stressed, it is not uncommon to see Tetras rapidly breathing, using up oxygen in the process. The aquarium must therefore be well oxygenated, by surface agitation from a filter or air pump. Water movement is preferable, but not essential providing oxygenation is sufficient. The oxygen factor is particularly important in planted aquariums, which may need additional aeration at night if Tetras are used. Under aquarium conditions, a heavily planted display is preferred by Tetras, and will result in noticeably better colours and health as well as an increased chance of spawning behaviour.
Clear water is also preferable, so good mechanical filtration combined with sensible feeding and good maintenance is essential. Remember that in fishkeeping terms, clear water does not relate to the colour of the water, but to the amount of suspended particles. Therefore, clear water can still be heavily discoloured by tannins from bogwood or peat filtration, and water discoloured in this way can also boost the overall health of many Tetras. Part of the benefit of such discoloured water is the effect of tannins and associated chemicals to acidify the water, creating closer conditions to the Tetras natural environment. Having said this, the acidity and/or alkalinity of aquarium water is not as important as it once was, as there are many more species which are now captive bred and have been raised in harder water. In either case, it is better to match your aquariums conditions to those of your shop, and only once your tank is stocked, to gradually adjust it to the ideal for the species.


Behaviour
Tetras are well known for being peaceful shoaling fish, but like many often called 'peaceful' fish; there is another side to the Tetra. Most tetras have a well-developed set of teeth and will quite happily use them to take bites out of long finned fish such as male Guppies and Siamese Fighting Fish. Generally speaking, the smaller more delicate looking Tetras such as the Neon's are fairly well behaved whilst the more stocky specimens such as Red Eyes, Serpaes, and Buenos Aires Tetras are likely to be a little more troublesome. Apart from this little problem, the majority of tetras are ideally suited to a community of peaceful fishes. Being a shoaling fish, all tetras should be kept in groups, and if kept in small numbers or on their own they may become distressed or loose colour and overall health. For some tetras, a system of status is used within a group, especially between males, and there can be frequent squabbles between individuals. Provided the fish are kept in a large group, such squabbles will very rarely be harmful in the long term. In a large group, any fish that wishes to stay out of trouble can simply avoid confrontations, whilst those which wish to reinforce or raise their status are free to pick fights with other dominant individuals. Some Tetras can show quite a lot of front towards other fish when they are unable to perform normal group behaviour. Keeping these fish in groups is therefore very important not only to give the fish the confidence and sense of safety that the group provides, but also to allow the fish to be aggressive and confrontational in an environment where other fish are not harmed.


Breeding
Tetras are egg scatterers and most will breed under good aquarium conditions. Soft water (up to 15dGH) with a pH between 5.5-7.5 and temperature between 24-26C (75-78F) will suit most species. The majority of species will spawn amongst plants or on a spawning mop after a courtship ritual, whilst a few will spawn near the surface amongst floating plants. In a community aquarium the eggs and/or young are almost certainly destined to be eaten, so if you plan to breed these fish you will need to set up a separate aquarium. The breeding aquarium should be bare bottomed for ease of maintenance, filtered through peat or contain tannins from bogwood, and be dimly lit. The eggs will hatch between 24-48 hours and the young fry will live from the egg sacs for a few days after which they should be fed on liquid fry foods or newly hatched brineshrimp.

Feeding
All tetras will take flake foods but it should be noted that in their natural environment tetras are micro-predators, feeding on tiny organisms and a wide variety of food types. In the aquarium, it is important to always try and recreate the natural diet as close as possible (I might add here that this does not include feeding of live fish to predators, which is neither good for the predator fish nor ethically justified) Good additions to the diet include either live or frozen Daphnia, Cyclops, Brineshrimp, and other small foods, as well as a wide variety of proprietary dried micro-pellets and flake foods.

Species
Choosing which Tetras to stock in your aquarium is, in most cases, a simple matter of taste. If you have any fish with extensive finnage such as male Guppies or Siamese Fighting Fish, you would be best to stick to the smaller Neons, Neon variants, Glowlights, and Phantom Tetras, which are less likely to nip. For harder water, providing your dealer also keeps the fish in moderately hard water, Tetras such as Red-Eyes, Black Widows, Buenos Aires, and Blind Cave Tetras are particularly adaptable. In all other cases, you can simply choose by preferred colour and shape, making sure that you purchase at least six of a type, in order to make a good sized shoal. Many fishkeepers prefer to keep a large group of one type rather than a few of several different species and this is often a much better way to create a nice looking display. For larger aquariums a shoal of the bigger Tetras such as Congo Tetras can look particularly impressive, and for well-planted tanks, Tetras with strong colours or markings such as Rummy-nose, Emperors, Black or Red Phantoms, and Cardinals will look particularly impressive.