The water was deeper then 50u, after little success I dug to the bed rock and got almost 100u. I was using the bionic and shadow at night. IDK, it was probably the few that got away. Other then that it was a great fishing trip, catch a bunch of colossuses and one child of aquarius.
Update: Got it! Left for a few hours irl. I came back left that planet behind. Went to the catalog menu looked up fungal mould, selected locate substance. The first system it sent me, had a toxic plant with deep water. It was also night, so all the box were check. Put the skiff out dawn was coming, the fourth catch was a whispering bonefish. Sun rises, Expedition done!