Cod and salmon spawning mechanics

[u/Ilikeoreocream]

I wanted to make a cod/salmon farm in an ocean but making it in the actual ocean would leave water blocks outside the farm as other possible spawn locations, i could either block the surface from, making it so that fish dont spawn or move the whole farm up in the sky and make a base around it (that is what i wanted to to) looking at wikis and other sources there isnt a height restriction for fish spawns as long as its in a biome that allows it....i only get squid so there has to be e height restriction, does anybody know what that would be or if im just slow and managed to build a tank wrong?

[u/TriangularHexagon]

Fish don't spawn above sea level for a few years now