When deciding on what shark to get, you want the best shark for your fish take. It first depends if you have a freshwater tank or a saltwater tank. The sharks that you'll find for freshwater tanks are not true sharks. They're not cartilaginous. They're bony fishes. Their fin patterns and their morphology closely resemble saltwater sharks, so for that reason they're called sharks, but they're not true sharks.
Saltwater is where you'd find the real sharks. For freshwater, most of the shark get very, very large. The iridescent sharks, tricolor sharks, they get really, really big, I mean, three to four feet in nature, but they happen to be very hardy. So you can keep them in a small aquarium, maybe 30 to 50 gallons in size. But they're going to quickly outgrow it, and it's cruel to keep a fish that gets three or four feet in nature restricted to a tank that's only three or four feet long. It's just really, really cruel, so I don't recommend a lot of the freshwater fish that are called sharks for home aquariums. If you have to have a freshwater fish that's called a shark, you can get a redtail shark. They don't get as big. The flying foxes kind of look like sharks. They don't get terribly large.
But for saltwater, the sharks that I would recommend are any of the cat sharks, bamboo, banded cats, dog chain. Those sharks stay on the bottom. Even the epaulettes from Australia, those are really cute sharks. They walk around on their pectoral fins. They also get large, so you want to make sure you have a large aquarium, but because they're not pelagic swimmers like black tips and white tips, any of the open swimming sharks, they're more suitable to home aquariums.
If you have to have something that looks like a great white or a baby great white, like a black tip, you're going to need a really large tank, and those tanks are very expensive. I'm talking, people would recommend a 200 to 300 gallon tank. I wouldn't put them in anything less than 1000 gallons. That tank needs to be round in shape. It needs to be eight to ten feet in diameter. They're just not going to fare well in anything smaller. And the upkeep and the maintenance on an aquarium like that is pretty staggering. You really have to know what you're doing. You need to have a lot of money or be really into this hobby to be that dedicated to keep one these open water reef sharks.
So to wrap it up, for saltwater, I would recommend one of the bottom-dwelling cat sharks. Nurse sharks are really good when they're small, but they get really large, so I don't feel that they're suitable for captivity. And then for freshwater, redtail sharks, tri-colors or balas sharks or iridescent sharks are great when they're small. But again, they're going to get really large and you're going to have to get them a much bigger tank, like the 200 to 300 gallon tank to keep them when they're adults.