This article, while not all encompassing, will take a stab at helping choose the right fish for your community aquarium. At least I hope it helps.
Articles like this are meant to assist new or only mildly experienced fish keepers as the typical clerk is neither experienced enough or knowledgeable enough to give you proper information. Sometimes they just don't care. For a test, if they are willing to sell you a tank and fish at the same time they are unscrupulous and buying anything there should be avoided.
So, let's take a look at the different types shall we.
There are many types of community fish. Live bearers (guppies, swordtails, platies and mollies) are a staple of the industry. But, I tell you the industry has changed. According to my contacts within the community this has been caused by severe inbreeding over the decades. They are not as robust as they were back in the early 70s. I can remember keeping all four types in one tank back then and this is virtually impossible now. Guppies are weaker, as are the others and Mollies now seem to be dependent upon the addition of some salt. Still, beautiful fish and Mollies at least will not eat their own young. If you do decide to go the live bearer route, please remember that you need a harem for each male. At least 3 females per male is desirable. If you have less than that and have multiple males they will fight. I won't cover the types as there are as many different varieties as there are stars in the sky, plus the mutt breeds. Whatever you choose is a matter of taste.
Tetras. Schooling fish and the home of the two brightest stars of the fresh water aquarium, the Neon and Cardinal. These require schools of 6 or more for best results. They are more fragile than other Tetras though, so you should never buy them to help cycle your tank...unless you like throwing away your money for they will die. Serpae Minor Tetras are more hardy and perfect for the beginner. Their red tint and white line along their fins is quite attractive. Another schooling fish, they do well in groups. There are many other types of Tetras. I have a preference, admitted, for the Black Neon, but there are many types prevalent in the aquarium trade and personal taste counts for much. Overall a good community fish.
Danios. I love these guys, particularly the long finned versions. The yellow tint to the bottom of the fins just gives a touch of color that I find pleasing. There is a genetic mutation called the leopard Danio as well. Another shoaling fish (schooling), they are hardy so very good for the beginning tank. A downside to them is the need for water movement. Without the movement they are very susceptible to spinal deformities. No mention of Danios would be complete without bringing up the Glofish. I mentioned these on someone else's article as being genuine, having been genetically modified so the color is true and passes down from generation to generation. The trade off is that they are even more susceptible to the common problem mentioned above, along with velvet disease. I have eschewed them because of this, but that is a personal preference.
Now we come to the ones I hate and I recommend you stay away from. LFS will try to push these off on you, but I will have no truck with them.
Chinese algae eaters. Avoid at all costs. As they mature they stop with the algae and tend to latch onto your fish. This is, needless to say, not an optimum situation. But none but the most professional of stores will tell you this.
Blueberry/Strawberry Tetras and Painted Glass fish. While good community fish, they are false fish. The correct name is Albino Tetra and Glass Fish. This link will take you to an article about that, far more encompassing than anything I could say and more stomach turning as well. Avoid these for they will fade since it is an artificial color.
Catfish and Plecos:
When I refer to catfish I mainly speak of the Corydoras and Brochis family. You will often see the Brochis listed as a Corydoras in the store, but they are a larger fish. You can tell by looking at the dorsal fin. Corydoras have 7 rays while a Brochis has 11 rays in that uppermost fin. All Corys and Brochis are good community fish, friendly and usually easy to maintain, but there are exceptions. Luckily, you are not likely to find the exceptions in your LFS, so we'll let that pass. These fish are good little scavengers who will work industriously to police up your stray scraps of food. They do *not*, however, feed on your fishes detritus, no matter what a clerk might say. There are no fish who do that so you'll just have to work on the tank maintenance yourself. Sorry for the letdown. Other catfish you might encounter are the Pictus (not suited for community tanks - very aggresive and will eat small Tetras), Upside down Catfish - peaceful and good for the community tank, Rafael Catfish - shy and mostly stays hidden, Bumble bee catfish, which are aggressive and should not be kept with small community fish and Channel Cats which can grow quite large.
Plecos are a favorite of mine. There are two things you should know and learn before buying one of these beautiful (to my mind) scavengers. First, not all of them are purely algae eaters. For example, the gorgeous L046 or Zebra Pleco requires meat in its' daily diet. Additionally, others require a good source of wood (they eat the algae off the wood and a bit of the wood itself). I can remember one of them whittling down my piece of decorative driftwood until the tip broke off. This kind of plays into the whole sponge filter thing I mentioned in my previous article as sponges are made out of fiber as well. Secondly, and most important of all, Plecos do not grow to the size of their environment. Oh no, they grow to their full size or near full size. Which means that regular old pleco the store is willing to sell you will keep on growing - up to about 2 feet long or so. Yeah, that's a little large for, say, a 20 gallon tank. They won't achieve their *full* growth, but they will outstrip the tank for sure. So, know what you are getting. This link takes you to the best source of all things Pleco that I have ever found on the internet. Consult it and know what you are getting. I recommend, for the smaller tanks, the rubber Pleco, Clown Pleco (either variety) or the smaller of the 2 Gold Nugget varieties. These all stay below 4 inches and are perfect for your smaller tank. Another one to consider, and very popular in the trade, is the Otocinclus. These miniature suckers are calm, gentle and industrious. And, unlike many, many Plecos they are not shy. You can often find 3 or 4 of them hanging on the front of your tank then quickly darting off to a better feeding area. Also, keep in mind that if you keep plecos you can kiss goodbye the chance of maintaining a live planted tank. Many of them will make short work of any live plants you have, particularly of the broad leaf variety.
Other fish common to the trade:
Glass catfish. What can I say. These guys are nice, but the store will not tell you that they *require* a school for survival. Individuals will quickly whither away and die. Oh, and they are natural diurnal predators, mainly living on bugs but occasionally eating smaller fish.
Hatchet fish. Jumpers. Schoolers. Top swimmers. These are a bit more of a headache to maintain, so be warned. Your tank must be fully covered or you will lose them to their jumping tendency.
Gouramis. Many of the Gouramis are not suitable for a community tank as they are semi aggressive to aggresive natured. Particularly the giant and 3 spot. The pygymy Gouramis and Dwarf Gouramis can be kept in a community tank. What they cannot be kept with, and that means none of them, is Betas. Both fish are what is called a Labyrinthine fish. This means they have an organ in their head, like a labyrinth, which absorbs oxygen. They can often be found gulping at the top of the tank and that is what they are doing. This means that as far as the Beta is concerned, with the long trailing fins of the Gourami, they are another Beta to be stalked. Sad but true. This can also be true with Angelfish. Not always, but you should be warned about the fact that it can happen. I've seen it, I've lived it and I no longer do Betas as I cannot keep them in small receptacles and have too wide a variety of other fish to ensure their happiness in a larger environment.
Clown loaches. I love these guys and they serve another purpose. Have you ever bought a fish only to discover, weeks later, an explosion of little brown snails? Trumpet snails, and they don't even require a pair to reproduce. Clown Loaches eat 'em. The chemical solution for getting rid of snails is deleterious to the health of other types of fish so go for the natural solution. They need a group of 3 or more, however, and will grow to 7 - 10 inches as full grown adults. So, if your tank is too small and you have this snail infestation consider freshwater crayfish or another snail known as an Assassin Snail. They also do the job. But, anyway, Clowns are peaceful and friendly, often clowning around the tank, hence the name.
Another favorite of mine, although many might not ever encounter them, are Kuhli Loaches, both the black and regular striped versions. These are fragile fish, unfortunately, which is why you might not encounter them. They really require a much finer substrate than the average gravel as they will burrow into the substrate. I had a colony of 18 of them at one time. Of course I probably had to buy 30 of them to achieve that, and imagine my horror when I lost every single one of them just changing tanks when my old one sprang a leak. Yeah, very fragile fish although there are others who claim they are hardy it's not been my experience. It could be the supply, but be warned you probably will most likely face a dismal survival rate.
Now, this article has gotten very long. There are many other types of fish. For more information stay away from chains and see if you can find a good independent store. Browse the wares and ask questions.
Next time around we'll visit the world of Cichlids and other oddballs of the aquarium industry. Until then, play nice and happy fish keeping!