The need for wild-caught protein to feed fish is so strong that there is krill piracy around antarctica!
https://apnews.com/article/whales-antarctica-krill-global-wa...
https://apnews.com/article/whales-antarctica-krill-global-wa...
1. Black Soldier Flies
2. Duckweed
3. Algae (Omega 3s)
All of the above are strong protein sources and duckweed and algae are fast growers and high density producers (at least an order of magnitude more than soybeans).Obviously more effort is required to farm them but with automation it should require minimal labor.