I remember reading an article about hatchery raised fish not having any idea what to be afraid of in the open water and because of this becoming very easy prey when they are released. I am sorry to admit that I really do not remember the source of the article, but it was about introducing potential killers within the hatchery environment and the reaction and possible learning process taking place. A few marauders were let loose in a run and they attacked, maimed and killed some fry. This caused a panic reaction not immediately but after a short period of time. As it turned out,the maimed and dying fry released a “panic” hormone in the water which alarmed the other fish. This hormone was released at the same time that the smell and pheromones of the attacking fish was in the water. After a few trial runs the small fry had the fear reaction when the attacker fish smell was released even when there were no wounded fish in the water. When the fry smelled the attacker they tried to hide. The fish that had not been exposed to actual attacks did not react to the attacker smell. Does anyone know if this technique is used by the DEC? And can we make this part of pen rearing?
I can envision a few predators in a net that they cannot get out of which is lowered into the pen. The fingerlings can get in and out of this net,thus creating a controlled hunting environment within a large safe pen. This might help prepare the small fish for the “real “world.
Five minutes after writing this thread I decided to try and find the article.
I just googled “conditioning hatchery fish” and there are several articles about the subject.