I've been keeping fish at home for about ten years now and recently, there is a theory about fish producing a hormone similar to the human GHIH hormone.
The reason why this theory has come about in the first place is because fish that are kept in smaller fish tanks with less water grow much less than fish that are in larger fish tanks with more water. Scientists believe that fish produce their own GHIH hormone which they release into the water. When the hormone builds up, their growth hormone becomes inhibited and they stop growing.
But when fish are in larger masses of water or when the tank water is changed often, they grow bigger possibly because their GHIH hormone is not building up in the water. This is definitely a lot different from the way our growth hormone inhibiting hormone works. But it still serves the same purpose. If we were to lack GHIH, our growth would also go out of hand because of excess growth hormone in our body.