If wewe mean that ALL dolphins were to be captured somehow and kept in tanks - then no. Dolphins should have the right to swim freely in the wild.
If wewe mean SOME dolphins should be kept in a tank, then yes. Reason for this (at least mine), is for conservation purposes.
Let's suppose that wewe have a breed of yellow (that i made up) dolphins that wewe have in an aquarium. That breed is dying out, and at a fast pace. So, kwa having those dolphins in that tank (assuming wewe are keeping it healthy, giving it a lot of space to swim and plenty of chances to interact with other dolphins), wewe not only preserve the EXISTANCE of those dolphins, but wewe also help bring those dolphins back to the wild.
If it's because it's injured au disabled somehow, then yes. If it's at a good place like Seaworld and will be released to the wild after a little while, then yes. If it's just for onyesha and will not ever kwa released, then no.