I have been making an aquarium/ sea life sanctuary in my minecraft world and I have spawned in dolphins, tropical fish, puffer fish, cod, salmon, and squid in an ocean biome with plenty of space to swim in. I even went as far as to name the dolphins and yet every animal except turtles have despawed after sometime not looking in the direction of the aquarium. There were plenty of ocean accessories including coral, kelp, sea grass, sea pickles, water(duh), and sand yet they have gone. What do I do? Is there a requirement I am not meeting?