For clarity the manual should state that amphibians can't mate and produce offspring. This is kind of implied by stating they are ambient creatures (which can't breed in vanilla either) but never explicitly mentioned in the guide.

Proposed change:
Animania amphibians are pretty much at the bottom of the foodchain. They are hunted by many Animals like Chickens, Hedgehogs and Ferrets. They are Ambient creatures, which means that they don't require food or water, don't have a sleep cycle and can't breed.