The short version sounds awkward because (as it's been said) any pond is basically "for fish". If you still keep this "for fish" in place, this could mean that this pond is specifically intended "for fish". Not for breeding only. For instance, you can just keep it in there, like you can put there some decorative fish. In this case the pond is not for swimming, not for washing.
For Fish only! No tresswimming!

The larger version sounds ok to me. This one sounds somewhat "lighter" than the FARM-thing.
Like it's just a pond with fish while a farm suggests some additional infrastructure like buildings for e.g. splicing, forage storages, etc.