What is going on with Blacktip reef shark?

[mr.r8rfan]

A friend of mine has two blacktip reef shark pups in a 1200 gallon aquarium and has had them now for about 3 months. They are about 18” in length, well he called me a little while ago to tell me that something had come out the anus of one of them and the shark was splashing around…he said it rose to the top of the tank and was floating on the surface while the shark was moving around. I have some experience with much smaller sharks but nothing like this so I wasn’t able to help him out. The description he gave me didn’t help too much either. He said it looked like a “taco” coming out and it was huge and the shark started splashing around all crazy then all of a sudden it sucked it back in. My best guess is it’s reproductive organ but I’m wondering if there are any other explanations and if this is normal behavior for this species in captivity.