The freshwater blue shark (cetopsis coecutiens) is actually a type of catfish and shouldn't be confused with the true blue shark (prionace glauca), a marine shark that can measure up to 13 feet long. These fish are found in the wild in the river basins of the Amazon, Tocantins and Orinoco. They're also known as whale catfish, blue cetopsis shark or blue shark catfish.
Adult blue sharks can reach up to roughly 10 1/2 inches, so they need a fairly big aquarium. The minimum size should be 48 inches wide, 18 inches deep and 18 inches high. They like a lot of open space to swim in, so decoration should be kept to a minimum, although they should have a small amount of cover, in the form of plants or driftwood. Sand or small, rounded gravel are the ideal types of substrate. Keep light levels fairly low.
Blue sharks are tropical freshwater fish, so they need to have their water heated to between 72 and 79 degrees Fahrenheit. The ideal pH should be between 6.0 and 7.4 and the hardness of the water should be between 2 and 15 degrees of general hardness. They like water that's well oxygenated and has a strong current running through it.
Blue sharks are voracious eaters, so they'll eat almost anything you offer them and don't require tempting with live foods. Feed frozen or dried meaty foods, such as prawns, mussels, earthworms, cockles and lancefish. Some individuals will even happily eat pellet foods. Be careful not to overfeed them, as they will gladly eat more than they need to.
As large and aggressive fish, blue sharks don't make good community fish. They're likely to eat any fish smaller than them, and they'll bite and attack bigger fish, too. As such, it's normally best to keep them alone. However, they're less likely to be aggressive towards others of their own species, so you could keep a group of two or more blue sharks.