@LadyCrescent,
If you're running a modded game, are you using S+? If so, the S+ Feeding Trough gives you the ability to exclude or include only certain dinos from using the trough, so you could set up a trough that only allows otters (for fish), and all the other carnivores will use other troughs
I am using this feature, but in reverse: I have a trough set up to exclude Rexs, so that forces my (ever growing) pack of Rexs to use a different trough. This stops the very hungry juveniles from eating all of the meat meant for the rest of my dinos.