If you have a large fish tank, which is one that is over one hundred gallons, you will most likely want to look at some larger fish to stock it. There are some great large fish available to the aquarium enthusiast, some of which will grow to over a foot in length and eat right out of your hand! Keep in mind that if you are going to buy a fish that grows over a foot, your tank should be at least eighteen inches wide, to give your fish the ability to turn around easily.
Oscars – Gentle Giants
Oscars are probably the most popular of the bigger aquarium fish. Oscars have the reputation of being violent and aggressive, perhaps because they prefer live food, such as feeder goldfish. They are not aggressive to fish that are their own size, and often are the recipients of aggression from other large fish. Oscars are in the cichlid family.
Loners in Your Tank
There are a couple of large fish that prefer to live solo. They are not compatible with other fish, and will attack and kill their tank mates, unless they are in a huge tank. The Red Devil falls into this category, as these feisty fish will claim at least one hundred gallons as their personal territory. Snakeheads also do not do well with other fish. Snakeheads are very strong, and some tank owners say they have broken the glass of their aquariums. This would be a species to consider only if you have experience with aggressive fish.
Arowanas are an interesting looking fish, but they get huge! They can grow up to three feet long! They are easily startled, and will fly out of the tank if they panic, so make sure you have a well-sealed lid if you keep these giants. They are peaceful fish when kept with fish close to their own size. Clown Knives are another peaceful big fish. They are prone to attack by fish that are more aggressive. Clown Knives are picky eaters, preferring live food. True Gouramis are another very peaceful big fish.
Pacus are another large fish, and can grow to be over fifty pounds! They are closely related to the piranha, but are vegetarians mostly. They will eat anything that fits into their mouths, so keep small fish away!
If you have a huge tank, one that is over 1000 gallons, you can own a Redtail Catfish. Redtail Cats will eat any fish that fits into their mouths. It is best not to even consider raising Redtail Cats if you do not have a huge tank, because they are susceptible to a fatal skin disease when kept in too small of a tank. Shovelnose Catfish grow from about eighteen inches to three feet. These cats also have large mouths, and can swallow fish that are up to half of their own size. These large fish tend to be very hardy, but need plenty of room!
Other Options for the Large Tank
Tinfoil Barbs are very fast fish, so they can sometimes be mixed with more aggressive fish since they can swim out of the way. These tend to be hardy fish. Iridescent Sharks are a peaceful fish that grows to about three feet. They are often attacked, even by peaceful fish, and will loose their eyes and fins. These fish like to move, and need plenty of room to swim.
Finally, if you are looking for an algae eater, choose with the Lyretail Plecostomus. The Lyretail Pleco can grow to be several feet long. They have a heavy body armor that makes them almost impossible to attack, so they can be kept with aggressive fish.