I'm sure I read somewhere that Maori fishermen used to eat small-mid sized fish and left the largest ones because they were the best breeders. I can't find a reference now but has logic.
I met a fella whose income came from going up coastal streams (canoe? Dingy with outboard?) to catch eels to sell. He definitely left the largest (queens?).
In most fish, larger size = more eggs or more sperm. So yes, largest ones are typically the best breeders. IIRC some species like I think some tuna they don't harvest the largest on purpose.
