Assessing emotional states in fish

Millot, S., Cerqueria, M., Castanheria, M.F., Øverli, Ø., Martins, C.I.M., Oliveira, R.F. (2014). Use of conditioned place preference/avoidance tests to assess affective states in fish. Applied Animal Behaviour Science, 154, 104-111

This study aimed to investigate whether place preference and avoidance tests can be used to accurately assess the emotional states of fish. The physiological and behavioural responses of gilthead sea bream to positive and negative situations were assessed.

In the first phase, study tanks were divided into two halves; one half plain white, and one half with dark polka-dots. The amount of time individual fish spent in each side of a tank was recorded to establish where they preferred to be.

During the stimulus phase of the study, half of the fish received the negative stimulus in their preferred tank side; this involved being chased by a net for 10 seconds every 2 minutes. The other half received a positive stimulus, which was the addition of food pellets every 30 seconds for 10 minutes in their non-preferred tank side. Following the treatments, the place preference test was repeated. The individual behaviour of the fish was observed throughout, and their plasma cortisol levels were measured afterwards.

Fish do remember

Fish given food pellets spent more time in their non-preferred side, while those exposed to the negative stimulus spent less time in their preferred side and showed an increase in cortisol. The study shows that behavioural and physiological measures can be used to validate place preference tests, and can be used as a way to assess emotions in fish. In addition, it shows that fish demonstrate the ability to retain positive and negative memories associated with their environment.

World Animal Protection’s view

We believe that given the wealth of evidence demonstrating that fish are sentient and capable of experiencing positive and negative emotions, greater consideration should be given to their welfare.