Forge 1.16.5 36.2.4 also tried with 36.2.19
Aquaculture 2 1.16.5-2.1.21
Prehistoric Fauna 1.16.5-2.1.1
BiomesOPlenty 1.16.5-13.1.0.477

So i got back to play a bit of minecraft and added Prehistoric Fauna to the pack.
Aquaculture fishes still spawned (at least in the big pack) but wherent fishable anymore.
So i removed this mod and it worked again.
But to confirm it i stripped my modlist to only the 3 mods u see above... and they still werent fishable .
Oddly removin all the other mods except those 3 caused the fishes to not even spawn in the overworld at all.

Well thats as much info as i can give to you.
Its a great mod and i rly dont wanna remove it.

Also experiencing this. Getting the issue with just this setup:

• Forge 36.2.31
• Aquaculture 2.1.22
• Prehistoric Fauna 2.1.3

The Aquaculture fish do spawn for me, as long as i stick around a little bit in newly generated chunks, not in spectator mode. When fishing in the overworld, I seem to only be getting vanilla drops, while once I remove Prehistoric Fauna I get Aquaculture drops, so perhaps there is an incompatibility with how the loot tables are implemented between the two.

This mod adjusts fishing. Maybe you can create a datapack to solve this problem?