Why don’t sharks in an aquarium eat the other fish?

Why don’t sharks in aquariums eat the other fish? This is the type of question that goes through my brain as I watch the fish swim around large aquariums. As someone who has an insatiable need to know these things, I posted the question on both my personal Facebook page and on my Google + page.
Of course, I received the usual tongue in cheek answers, some of which were quite funny: “They ran out of tartar sauce” Some of them were serious answers: “They are well fed.” So, knowing that once a question is rolling around in my head and that I will think about it forever until I get answer it, I decided to find out. Of course, like any good modern writer, my first act was to Googled it. We all know that any research starts with Google these days. Unfortunately, I was not happy with the results. The question brought up many answers but most were opinion and not fact. So, back to social media I went and asked if any of my friends or subscribers were Marine Biologists. I wanted a real answer, not an opinion. And I got answers.

Most of the answers were similar although there were some differing points. This is some of what I received.

Answer 1:
Sharks are lazy. Depending on the species, of course – most sharks that you see in aquariums are white or black tipped reef, nurse and dogfish. None of them aggressive enough to actively pursue anything in there since they are all fed fairly well. I do know that at the Columbus Zoo in Ohio, they lose about 8 fish a day to sharks, but usually as “accidents” – they get into a food swirl and the sharks eat what is in front of them. Nurse sharks are especially lazy. They are known to lie motionless under coral shelves for hours, dispelling the myth that sharks must always be in forward motion to breathe….I could say much more, but bottom line is that they are just domesticated enough to know they don’t have to chew on anything that might outrun them in the tank…
The theory that they stock off-diet fish is also not quite true – a hungry shark will gnaw on almost anything – leading back to the fact that they are well fed.
Answer 2:
[Sic]I do know that occasionally (more frequently?) sharks WILL eat other fish, including other sharks, in aquaria. However, many sharks do not have to feed frequently and I assume the amount they receive from the staff probably keeps them from attacking other fish very frequently. It is often difficult for an aquarium to restock certain fish species because they are not close to the ocean or they are restrained by limits placed on their collecting permits.

Answer 3:
The sharks are well fed and sharks are opportunistic feeders.if they do not have to exert the energy to hunt they will not. AND most aquariums stock other fish that are not on the normal diet of the particular shark.
And lastly, Answer 4:
Though sharks are viewed as eating machines constantly in search of food, this is definitely not the truth. Our large sharks are fed three times a week. Each shark is fed individually so our aquarists insure that the dietary needs of each animal are met. Sharks are also opportunistic hunters. They tend to feed on prey that is weak, sick or injured. Because our sharks are fed a healthy diet, and the fish that reside with them are healthy, the sharks do not need to expend the energy to chase their co-inhabitants for food.

So the prevailing answer seems to be that the sharks are fat and happy. Since they do not have to feed themselves or look for their food, they have no interest in going after the other fish. It also seems that they do occasionally eat the other fish. Although it perhaps more of an accident, or opportunity, rather than actual hunting (a midnight snack?) that happens to fall into their jaws.

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