Dolphins don't die if not rendered

When we trap a dolphin and give it a name, we think it will not despown. In fact, they don't despown if they have a name. The problem is that, when the dolphin is not in our render distance for a few minutes, it dies because it needs air and water. Unfortunatly, the game froze the dolphin, so it's only in water or in air. Mojang could add a feature that make the dolphine invincible if it isn't in the render distance