My dad was a commerical fisherman (trap nets) in Michigan's Great Lakes as I grew up. And the sea lamprey came into the lakes..
my job was to pull the yucky things off the whitefish which he caught and throw them into a barrel of very strong salt water - it killed them and a neighbor used the dead ones for fertilizer, WW2. It was a real mess for the lakes a really decimated the fisheries eventually the state introduced electric weirs and poisons at the mouth of rivers and streams.....millions of dollars of damage.