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Do Sharks Really Outgrow Their Tanks?

shark at The Beijing Aquarium

Watching fish swim around is relaxing, but are they going to get too big for their tank? Maybe. It all depends on the fish and the atmosphere of the container that you’re keeping them in.

Keeping a Fish Tank

Here are some basics when it comes to having a fish tank. The size of the tank and the size of the fish you’re putting in your tank matter, but you want to consider how big your chosen fish are likely to get. No, they won’t “grow to the size of the tank,” but they could outgrow it, or not grow enough.

The rule for fish living in tanks is that you only want one inch of fish per gallon. That’s one inch at the fish’s full-grown size. Meaning, in a five-gallon, tank you wouldn’t even be able to have a plecostomus fish (one of those cool bottom feeders that help keep your tank clean) because they can grow to over a foot long. While putting a pleco in a small tank may stunt its growth, it’s more likely it will outgrow the tank or die.

Even your average feeder goldfish can outgrow the tank you put it in. After all, goldfish are a species of carp. My mom kept freshwater fishtanks as I was growing up. We had an aquatic frog that spent all of its time underwater and lived off feeder goldfish. Two of them managed to outwit the frog, and within a year, they were both were pond-sized, leaving no room in the 25-gallon tank for other fish.

Before you invest in a tank, you need to take the time to research the fish you want to keep and learn how big they can get. While an overcrowded tank may seem like a way to stunt the growth of fish, you’re more likely to kill them. Tanks containing too many fish are more susceptible to disease as well (just take a good look in the tanks at big box stores that sell aquarium fish).

A quick online search of any type of fish, from mollies to swordtails, to red-tail sharks, to silver cats, will help you find out which fish grow the largest, which ones stay smaller, and what you can expect with your preferred aquarium dwellers.

Keeping Sharks

Not all sharks are created equal. You can keep sharks in your 20-plus-gallon freshwater tank that grow to a foot or more. These aren’t actually sharks, though. The freshwater sharks you buy at the pet store are most often catfish or a carp species.

Real sharks, however, are becoming a popular household pet (at least for those who can afford the tanks to keep them in). You need a pretty big tank to keep a saltwater shark as a pet, and lots of money to keep them fed. You can’t get away with fish flakes!

If you’ve been thinking about keeping a shark as a pet, whether you’re looking at a docile nurse shark or something scary, you need to keep in mind the risks, not only to the sharks you keep but also to your home and family. Implementing a 180-plus-gallon fishtank is expensive, and so is the upkeep.

You also need to do some research on sharks. Because they’re legal to keep as pets, as long as they’re not a protected species, you’ll have a few species from which to choose. However, you want to pick a species that won’t mind being kept in captivity and won’t outgrow your tank. Sure, you can keep 18 sharks that max out at 10 feet in a 180-gallon tank, but you’ll also want to leave room for their live food. And, just because an average nurse shark might max out at 14 feet doesn’t mean they can’t grow any bigger than that.

When your basic aquarium fish, such as goldfish and catfish, outgrow their tanks, you can invest in a tank the next size up without much fuss. However, when you have a nearly 200-gallon custom-built tank in your home and your bamboo sharks outgrow it, what are you going to do? And what if your 10-feet or longer fish (sharks or not) die? You can’t flush that down the toilet.

Yvonne Glasgow Yvonne Glasgow
Yvonne Glasgow has been a professional writer for almost two decades. Yvonne has worked for nutritionists, start-ups, dating companies, SEO firms, newspapers, board game companies, and much more as a writer and editor. She's also a published poet and a short story writer. Read Full Bio »