It's easy for people looking at the wide selection of fish at the pet store to be tempted to buy a fish they don't know much about because they like the looks of it; unfortunately this can often lead to incompatible fish or an incompatible tank and the fish is the one that gets to suffer for the purchaser's ignorance. Many people even see a little information card informing them that this particular fish reaches very large sizes but perhaps they suscribe to the widely-accepted myth that fish grow to the size of their tank...and that's exactly what it is, a myth. While it is true that fish secrete a growth hormone to keep from entirely growing out of their tank it is equally true that they generally do not stop growing until they are already too large to live comfortably in the tank, their life spans will be shortened by stunting induced by inappropriate housing, and they will never reach their full potential for health and beauty. Some types of fish such as Oscars or Gouramis have a slightly different reaction to that growth hormone...only their heads stop growing, so eventually that poor fish's mouth will morph by the body's continuing growth until the fish can no longer eat and then it dies a slow and painful death.

Since you're reading this article I can assume that you are a caring and responsible pet owner who wants to learn what you can to properly care for your pet...perhaps you're looking at adding new fish, maybe you've made the mistake of buying the wrong one for your tank before and are trying to avoid doing it again, whatever the reason you have taken a responsible step in researching these pets. Please be aware that this is only a listing of popular freshwater fish that are often subjected to mistreatment due largely to their adult size (most are sold in pet stores as babies) and you should definitely research any pet you're planning on buying in-depth before making the decision.

Goldfish - These rank at the very top because they are the single most abused animal in the United States (I can't speak for other countries as I've never done research on those statistics) and a lot of it is due to their unique size requirements and their ready availability at affordable prices in stores. No, a goldfish is not a "throwaway pet", they are exceptionally hardy and if cared for properly can live for up to...drum roll please...30 years! These are one of those fish that will stop growing entirely if the tank is too small (but are often already too big when they stop growing) and will almost certainly have a significantly reduced life span from the stunting. A single-tailed goldfish such as a common, comet, or shubunkin can and often do reach sizes upward of 16" and need at least 30 gallons per fish with a tank at least four times their size in length and twice their size in width (a size parameter that holds true for most large fish). A double-tailed goldfish such as a ryukin, lionhead, or pearlscale may only reach 8" in length and don't need as much free swim space because of their build but still need a good 10-15 gallons each (more for some of the larger fancies such as orandas). Sadly goldfish bowls are still in common usage and are one of the worst environments for that fish due to improper or no filtering, exceedingly small spaces, and not enough water changes. Bear in mind that goldfish also produce a lot of waste and will need some very strong filtration...for more specifics on proper goldfish care check out the resources available at http://www.kokosgoldfish.com (please note, I am not affiliated with this site in any way, it is merely the best site I've ever found for goldfish information).

Tinfoil Barbs - Easily and quickly reaching sizes up to 14" with an attitude to match, these fish are often purchased in the belief that they will get along just fine with their smaller barb cousins such as the Tiger Barb or Gold Barb where in actuality the Tinfoil will be able to cheerfully snack on these smaller fish within a couple short months. These fish are active and an attractive silver with black fins that are often bought for their looks without any prior knowledge regarding their temperment or size requirements.

Oscars - I'd like to think most people know what they're getting into with these fish but sadly I'm discovering that that just isn't true. Less than a year ago I had a customer ignore my assertion that the Oscar he was eyeing would not fit in his 10 gallon tank...after all, the fish was only 3" long! He was one of the better ones, though, in that the man returned the fish four months later when the fish had nearly tripled his size rather than making him suffer in a tank unsuited to him as is sadly still common practice. I'd also like to think that this common practice is due to pet owners not knowing any better rather than willfully abusing their fish but unfortunately that's not always true either.

Pacus - There are many different species of Pacus, the ones I see most around here are Red-Bellied Pacus but all are closely related to piranhas, have varying levels of aggressiveness, and all get quite large...many over a foot long. A Pacu is a very attractive and outgoing fish but will be a major problem in your tank if you haven't planned properly for him ahead of time.

Silver Dollars - Relatively small in this company, the silver dollar generally grows to around 8" in diameter...which is still pretty big compared to most of the popular community fish out there! Silver Dollars prefer to be in groups, and a group of 8" fish takes up a lot of space very fast.

Gouramis - Gouramis come in a variety of sizes but all are pretty large...generally sold in pet stores around 2"-3" Gold Gouramis, Blue Gouramis, Pearl Gouramis and the like reach about 8" while Kissing Gouramis hit up to 12" and Giant Gouramis grow to a whopping 28"! There are some smaller Dwarf Gouramis that only grow 4"-5", but be absolutely certain you know what you're getting before you buy them, you don't want to expect 5" and end up with two feet.

Knife Fish - Knife fish are a very attractive fish that is also seen in pet stores at just about 2" long...but the Ghost Knife can reach sizes of up to 20", the Banded Knife can get to 24", the Glass Knife hits around 18", and my absolute favorite the Clown Knife can reach a whopping 40" in length. These are exceedingly interesting fish to look at (my sister thinks they're creepy when they're big though) and can make some gorgeous specimens if kept properly.

Irridescent Shark - Another fish I often see being sold at Wal-Mart at the adorable size of about 2" long and collected by numerous aquarists who can't understand why their peaceful community fish start disappearing and start wondering when that fish will stop growing. Truth is these attractive little fish need at very least 135 gallons in a long tank and reach sizes of 40". Sadly very few of these fish get to live out their entire life span due to misunderstandings about them and often die within a year or two either from overcrowding or inappropriate water parameters (they can get somewhat picky about that).

Common Plecostomus - Another very widely abused fish that can reach over two feet in size. Unlike some of the carnivorous giants the Pleco can take up to a couple of years to reach its full size so it can sneak up on you and reign destruction on your tank décor as it gets larger and more crowded.

Pomacea canaliculata - while not a fish I nevertheless felt that these snails deserved a mention...while most "mystery snails" (apple snails) sold in pet stores are Pomacea bridgesii, or Brigs, some do on occasion get canaliculata, or Canas. Canas look, to the untrained eye, nearly identical to Brigs with one important difference. While a Brig grows to about the size of a golf ball and needs about 2 ½ gallons each, a Cana reaches the size of a softball and needs about 10 gallons all to itself. As with all apple snails Canas cannot be expected to live on algae alone and need some greens or snail cookies that are high in calcium to ensure their health and they are very messy creatures that require the same level of filtration you would afford to a goldfish. For more information on the care of apple snails and how to spot a Cana check out http://www.applesnail.net (again, no affiliation, I just think it's an excellent site).

This is by no means a comprehensive list and I will probably be adding to it as time goes by, merely some of the most common freshwater fish that are still suffering widespread abuse because of their size and individual needs. I implore anyone who is thinking of getting a fish or has problems with the fish they have to thoroughly research every aspect of their care to ensure they're being cared for properly...if it's something you wouldn't do to a dog why is it alright to do it to a fish? Thank you for taking the time to further your understanding of these amazing animals.