It says in Chullin 127a that all found on land is found also in the sea, except a "chuldah". Is there is a larger list of such fish (other than the Gemara mentions)? Any insights would be appreciated as to what is being taught here.
The idea is simple and it's called Symmetry.
Our world is created symmetrical - there's good and bad, there's heaven and Earth, there's man and woman, there's waters and land etc. While they are not "exactly" the same, there's a resemblance with a different "vector". That provides the necessary equilibrium in the creation.
The life on Earth was divided between the sea and the land. Theoretically they should mimic each other and that what the Gemmorah claims.