The weights seem severely off to me.
Granted I know quite little about fish biology but a dog the size of the first fish would be 15kg easily I reckon if not 20. The second more like 50 kg.
But maybe fish are less dense to ensure buoyancy or something.
yeah some of the diamond fish i dont understand the weight system either. the silver-golds are more believable with the weight but the diamonds are just big for the take of being big i think