Canadian researchers found that trout could learn to avoid a net placed in their tank by fleeing through an underwater doorway. They then learnt to anticipate the net by remembering that it would plunge in 10 seconds after a light went on. The research demonstrates memory and reasoning in fish.
"Fish were placed individually into a two-chambered shuttle tank where it could be subjected to the putative frightening stimulus of a plunging dip net in either chamber. The fish could escape from the stimulus by swimming through a doorway to the other chamber. The fish escaped from the plunging net by swimming through the doorway, some on the first occasion and all after a few exposures. Each fish was then presented with a neutral stimulus of a light that went on 10 s before the net plunged into the water."
"Over a 5-day period, all fish learned to avoid the plunging net by swimming through the doorway when the light was illuminated."
TROUT REMEMBER TO AVOID NET AFTER 7 DAYS OF NO TESTING
"All fish showed evidence of longer-term memory by showing the learned avoidance response on the first occasion they were tested after 7 days of no testing."
MEMORY AND FEAR DISPLAYED
"Whereas the escape responses to the plunging net were immediate and reflexive-like, the avoidance responses to the light going on were delayed a few seconds and more deliberate in nature. This evidence suggests that trout can experience fear and that they can learn to avoid frightening stimuli. It implies that they are sentient animals, more complex than previously thought."
"The trout in this experiment demonstrated the ability for both short-term and long-term memory."
"The present finding, that trout have the ability to remember an avoidance response in the short-term and longer-term, is in accordance with results obtained from other species of fish."
"The trout in the current study, having been exposed to the potential danger of a plunging net, may have retained a memory of it for an even longer time period than was tested."
"These results show that fish can learn, have memory and make conscious decisions to avoid being exposed to a sudden and intense stimulus when given a cue that such a stimulus is going to occur. In other words, the results suggest that fish can experience fear."
"Taken together with the recent evidence that fish can suffer in other ways e.g. by experiencing pain the results suggest that fish may be worthy of more moral consideration than they have had in the past."