Will that fish do well in my tank? Can I keep that fish with my guppies? Will that fish outgrow my 20-gallon aquarium? If you have you ever asked these or similar questions, has the response been tentative or later proved wrong? With the hundreds of species of fishes available in even a moderate size pet store these days, it is difficult, if not impossible, for the average aquarist to know or remember what each and every one will require for maintenance and good health. How then can we know which fish to choose for our aquariums while avoiding compatibility problem later on?

There is a way out of this dilemma. You may already know many of the answers and not realize it. Picture in your mind a catfish. Now picture a tetra. They are different, aren't they? And yet I did not tell you what specific fish I was talking about in either case. There are hundreds of catfish, and they differ in many ways from each other. Some are no more than 1-inch long, whereas others grow many feet in length. Still, the word "catfish" conveyed a meaningful impression. The question is, why?

The word catfish is generally accepted as the name of a group of fish that exhibit many similar characteristics. The same is also true for other groups of fishes. This then is the key to the dilemma raised at the beginning of this article. Of the many, many fishes available, the vast majority belong to just a small number of groups. You probably already know quite a bit about each group. By paying attention to these groups, you will be able to select fish for your community aquarium with a minimum of difficulty.

Scientists classify all plants and animals, including fish, according to a scheme that has as its three lowest major divisions the following terms: family, genus and species. The genus and species are the "name" of the fish in question. Each fish is placed in a family that reflects it's evolutionary place in this world. In turn, the families are grouped into larger divisions. It is of value to us that this placement also normally reflects strong similarities in behavior and maintenance requirements. The vast majority of the fish available to us are members of just seven families or groups of closely related families.

This article is devoted to a discussion of these seven groups. I will explain how to recognize them and what their general care requirements are. Before proceeding, I must mention that there are fish commonly available that are not members of any of these groups, and that within each group there are exceptions to every generalization. Nevertheless, a broad understanding of each group will be of great help. The exceptions in each group are interesting in their own right — just because they are exceptions — and can provide you with great satisfaction as you learn to recognize them also.

The main groups are the tetras, the barbs, the catfish, the loaches, the livebearers, the cichlids and the labyrinth fishes. Five of these each represent a single scientific family. The other two, catfish and the labyrinth fishes, are groups of closely related families. There is another large group, the killifish, but these are seldom as available to the new aquarist and will not be discussed here.

The Tetras
Picture a neon tetra, a black tetra, a lemon tetra, a cardinal tetra. The tetras are all members of a family called Characidae. They and members of several closely related families come from South America and tropical Africa. There are several hundred different species. In general, these fish are small, ranging from 1 to approximately 2 inches in length. They are active swimmers and spend their time in the upper half of the aquarium.

The tetras offer fairly bright colors, with silver, black and shades of red predominating. They display best in a small school in tanks with a large open area in front and some plants in the background. They accept all standard aquarium fare and are very competitive eaters. A varied diet is best, of course.

The tetras will coexist with most other fish who cannot have them for lunch. Except for breeding, the tetras do not require any special water conditions. Given proper water conditions and food, most of the tetras are easily bred. However, their fry are very difficult to raise, requiring very small food and very sanitary conditions. These requirements usually preclude all but advanced aquarists from rearing the young.

In summary, for active color in the mid to upper levels of a tank, any member of this group is an ideal choice. For best effect and normal behavior, a school of six or more of the same kind works better than one or two each of several different kinds.

The Barbs
The fish known as the barbs are a subset of a group of fish commonly referred to as the carps and barbs. They all represent members of the family Cyprinidae. These fish are somewhat similar to the tetras. Most of the barbs are stockier and larger than the tetras, with many in the 2- to 4-inch range, although a few get considerably larger.

Typical of the most common representatives are the cherry barb, the rosy barb and the tiger barb. The best known of the large members is the tinfoil barb. These fish are less colorful than the tetras but are larger and show up better from a distance. The predominant colors are silver and gold with some black and red highlights.

To discern the difference between barbs and tetras, look for the stockier fish with a coarser appearance (due to larger scales). Also, most of the Cyprinidae have barbels. These are small whiskers on the lower jaw of the fish. In addition, barbs do not have an adipose fin, whereas the charicins all do. The adipose fin is a small "flesh-like" fin on top of the fish behind the dorsal fin. Also included in the Cyprinidae family are the danios and rasboras. While these could be mistaken for members of the characins, their maintenance is the same as the barbs.

The barbs are active swimmers and prefer the upper areas of the tank. Although not as strongly inclined to school as the tetras, they do appreciate the company of their own kind. They will thrive in a wide range of water conditions. Like the tetras, these fish will accept all standard aquarium foods.

The barbs can be induced to spawn under aquarium conditions. They scatter their eggs in fine-leaved plants. The parents will promptly eat the eggs, however, and normally some provision must be made to prevent this from happening. The fry are considerably larger than those of the tetras, and therefore are much easier to raise. They are a good choice for your first attempt at breeding fish if you are so inclined. A particularly good choice would be the zebra danio.

Goldfish are a colder water member of this group that have been breed in captivity for many, many generations to develop the numerous variations of shape, color and finnage available today. Because goldfish are not tropical fish, they should never be kept with warmer water species.

The Catfish
Everybody knows what catfish are — they have whiskers, right? Actually, yes, the distinguishing feature of catfish is that they have barbels (whiskers). In most, but not all, catfish, these barbels are quite prominent and readily noticeable. The other distinguishing characteristic of catfish is that they do not have scales.

You probably thought all fish had scales. And you might ask, "What is that I see on the sides of my Corydoras?" The fact is, no catfish has scales. Many have bony plates that look like large scales, but some do not have even these. The coloration of most catfish is restricted to shades of brown, black and white. There are a few spectacularly colored exceptions.

Many people consider catfish to be ugly or weird in appearance and a necessary evil as scavengers. Fortunately, this outdated viewpoint is fading and people are starting to appreciate catfish in their own right.

The catfish belong to not one but 32 different families, the vast majority of which come from freshwater environments. They inhabit every continent except Antarctica. They are also the most diversified of our groups. There are more than 2000 different species. They range in size from less than an inch to several feet. However, the majority of those available at reasonable prices tend to be from 2 to 6 inches when full grown. Most are bottom fish. That is, they will spend the majority of their time on the bottom and will actively search for food using those whiskers. Some are nocturnal and therefore active only at night.

In selecting catfish for your tank, the most important consideration is whether or not they will get along with the other residents. Although catfish are less likely to be eaten than many other fish, it is not impossible if there is enough of a size difference. Another consideration is whether the catfish will reverse the situation and eat their tankmates. Many catfish are piscivorous, meaning they are "fish eaters." To determine their feeding preferences, look at the mouth of each species. If it is pointing downward or is a sucker mouth, you are probably safe. If, however, the mouth is large and/or points forward, beware! Predatory catfish are not to be trusted in a community tank. For example, there is a common fish, sold as an "angelicus catfish," that is silver with black stripes. It is very striking in appearance. Many are sold as being harmless. As long as they are small, this is true. But they grow fast and at 3 or 4 inches will eat any fish they can catch, up to three-quarters of their own size.

Catfish are not fussy eaters, but neither should they be neglected and just allowed to scavenge off the remains left by the other fish. Although often sold as scavengers for community tanks, catfish require the same nutritious foods that other aquarium fish need. Feed your catfish with food that sinks to the bottom of the tank and they will reward you with many hours of pleasure, for they are very long lived and hardy. Many of the catfish can be bred in aquariums, and some are raised in huge quantities commercially. Others, however, have never been bred in captivity.

The Loaches
Often confused with the catfish, these fish belong to the family Cobitidae. They are mostly from southeast Asia and India. Loaches tend to be longer and more rounded than the catfish, approaching a worm or eel shape in the extreme, such as the ever popular coolie loaches. They exhibit the same colors as the catfish, with additional brightness and oranges, resulting in some very beautiful fish, such as the clown loach.

Although not quite as hardy as the catfish, they will do very well in most waters, particularly if well fed. Many members of this group are secretive, coming out only to feed at night. Often, aquarists will go weeks at a time between "sightings." Don't let this last statement prevent you from trying some of these fishes. Their biggest drawing card is their antics. Clown loaches, for example, will sometimes roll over and play dead.

The Livebearers
The livebearers are best characterized by their name. They all give birth to live young that are miniature versions of their parents. Interestingly, in the aquarium literature of the 1930s, these fish were often divided into two groups: livebearers and egglayers.

These fish are members of the family Poeciliidae and come from southern North America, Central America and the Caribbean Islands. Many live near the coast, often in brackish waters. They tend to be small fish, on the order of a few inches in length, with the male often smaller and more colorful than the female. These fish have been bred in captivity for many generations, resulting in a wide variety of color strains with different kinds of finnage. There are also hybrids.

These fish do very well in the harder, more alkaline waters that come from the taps in most parts of this country. They appreciate, and some species require, the addition of a small amount of salt in their water. While they will accept any and all foods that are small enough for them to swallow, these fish are primarily carnivorous, feeding on insect larva in the wild. In fact, members of this family often play important roles in mosquito control programs. They will thrive much better if you give them a little "meat" in their diet. The popular mollies are an exception and do best with the addition of vegetable matter to the diet.

The outstanding feature of these fish is their production of live young. The fry are large and can eat within minutes of birth. They will reproduce in a community tank. However, the parents will quickly eat any young they can find. If you wish to save more than a few of the fry, steps need to be taken almost immediately after birth to separate the parents from the young.

The Cichlids
The members of the family Cichlidae are the notorious bad guys of the aquarium hobby. They have a reputation as bullies. Why then are they the most popular of fishes among advanced aquarists?

The cichlids are a very diversified family from Central and South America and tropical Africa, with even a few from the Southeast Asia and the Indian subcontinent. This is the one family that destroys my hypothesis that the maintenance requirements can be well established if you know what family a fish belongs to. This family includes fish with special water requirements on both ends of the scale. Almost all cichlids are less tolerant of laxity in the maintenance of good water quality than other tropicals. Cichlids include fish as gentle as the discus and angelfish and others that are self-propelled fish eaters (or as a friend said recently, a "swimming attitude problem").

Most cichlids have a classical fish shape. They tend to have very prominent fins and posses all of the colors of the rainbow. They come in subdued colors and in gaudy ones. They range in size from 1½ to 10 inches or more. Some will eat almost anything that can be thrown into the tank, whereas others have specialized feeding requirements.

Why are they popular? Quite simply because of their behavior. They are among the most intelligent of fishes. Many come to recognize their owner from other humans, and some know when feeding time is and will protest or remind you if you forget. They exhibit very elaborate spawning rituals and practice care and protection of their young in numerous ways. The observation of a pair of cichlids raising their young, feeding them and protecting them is among the most satisfying experiences in the hobby.

Don't let their reputation prevent you from investigating these fish. At the same time, do not buy a cichlid on impulse until you have had time to investigate its needs further and are prepared to provide suitable quarters.

The Labyrinth Fish
The labyrinth fishes are members of four closely related families. The majority of the readily available fish belong to the family Belontiidae. They are commonly known as the gouramis, the betta and their close relatives. All of these fish posses a means for breathing atmospheric air, called a labyrinth. Thus the name. To recognize these fish, look for specimens of 2 to 4 inches that are considerably "taller" than they are wide. They are brightly colored, with some of the smallest members (e.g., the dwarf gourami) possessing the best coloration. In some species, the females are less colorful than the males.

These fish prefer the top portion of the tank for their home. They do best in water that is a little warmer than the temperatures preferred by many of the other fish we commonly keep. Members of this family tend to feed from the surface and should therefore be provided with foods that float.

Although a few can get a little nasty, the majority are quite peaceful and can be kept with several of their own kind or with a couple each of several different kinds. Their tank should definitely contain some plants for shelter and to provide a feeling of security. The addition of floating plants will add greatly to the well being of the labyrinth fishes.

These fish exhibit a very interesting breeding behavior. They build a nest at the surface of the water. Sometimes bits of plant are incorporated or the nest is placed under leaves or other objects. The nest is constructed by the males with bubbles formed of air and saliva. Spawning occurs under the nest, and the eggs are placed in the nest by the male, who then guards and cares for the nest and eggs while they develop. This care is sometimes extended to the new fry for a while. The observation of this process will more than reward you for any effort necessary to keep these fish.

The next time you are in your favorite aquarium store, look at the tanks and try to place each fish you see in one of the groups we have just discussed. It may take some practice, but when you can do this with a fair degree of accuracy, you will have come a long way toward knowing which fish to take home and which to leave until next time.