If you've ever encountered an adult bamboo shark in a tank that is far too small, you will see how obese a shark can really get.
The same goes for Nurse sharks in almost every public aquarium that houses them. Nurse sharks are very sedentary in captivty. When put in a large display with Ram ventilators in it also, and bony fish, the Nurses are able to over-eat . On top of the over abundance of food in such displays, and on a more frequent basis, the Nurses expend an exponentially smaller amount of energy feeding than if they actually had to hunt, as they naturally do.
The same goes with Bamboos and hobbiest tanks. When I adopted several "adult" sized bamboos from a smaller tank, they had also been overfed, we're not used to searching or swimming to find food either. When placed in my pond/lagoon, the sharks I had had from juvenile stages were out-competing the new sharks when I fed. The older sharks knew the routine, that I broadcast fed and they had to sort of fight for the best pieces, even though I'd make sure everyone was getting their share in the end. The newer sharks had no idea what was happening! They would smell/sense the food in the water, but expected it to plop right down in front of them! Needless to say, they learned how to "compete" with the rest and it also led to a loss of a large amount of fat in the abdomen. Increased exercise eventually led to a more muscular look across the back, posterior to the shoulders.
As for shrimp and feeder fish available in the tank...
I find it to be a great idea however there are several pitfalls. One major pitfall is the necessary intense/thorough Quarantining of both marine feeder shrimp and whichever euryhaline feeder fish you choose. I use killifish that are available from a trusted bait shop who's holding tanks are extremely well kept, and properly filtered. During the summers I purchase them as soon as he gets his order each week while they are in full freshwater. I then acclimate to saltwater and prophylactically treat and watch the hill is for 6-9 months some times!
When I receive marine shrimp, I also prefer to receive them in FW, so that the acclimation to Salt may eradicate some of the ecto parasites as would a FW dip does yet vice versa. Feeder anything can be loaded with bacteria, viral, protozoan etc. pathogens.
If you choose to do it, make sure they are not severely ill. FW mollies are great in that they readily breed and provide small food items to other fishes as well.
