In this research, goldfish and trout were given mild electric shocks when they entered a particular part of their tank. The fish swam away when this happened, their respiration went up, and cortisol, an indicator of stress, went up in their blood. The fish learnt to spend time at one end of tank, away from the electric shocks, especially on the second day.
Trout together in a group were more likely to tolerate the more milder voltage.
"This plasticity in learning suggests that pain responses are not just confined to lower brain reflex actions, but to some degree, involve perception."
"Current legislation is written under the assumption that fish are incapable of perceiving pain and if there is any possibility that this is incorrect, new legislation will have to be developed to improve aquaculture conditions and change fishing practices."