Case Studies

New research shows fish have feelings too

Leia Rogers

Next time you enter the country’s waterways, be careful what you say because you never know who you might offend.

Interesting new research from a Charles Sturt University student in the School of Animal and Veterinary Sciences in Wagga Wagga has proven there is more to fish than meets the eye.

In her paper to be published in online journal PLOS ONE titled ‘Aggressive encounters lead to negative affective state in fish’, Ms Leia Rogers has noticed similarities in the emotions of humans and fish.

“It is so exciting for me to have my first published paper, especially on fish behaviour,” she said.

“By understanding how they perceive their experiences and how that affects their decisions, we will be able to help answer the question: ‘do fish have feelings?’.”

Ms Rogers, an Institute of Land, Water and Society PhD scholarship recipient studying fish behaviour and ecology of native and freshwater fish, conducted an experiment with six hatchery-raised Murray cod housed in a tank with five compartments, where two compartments were used to train the fish to have a desired response.

Ms Rogers taught the fish to approach one compartment by making it a positive experience with a food reward whenever it was opened.

The opposite compartment was used to train the fish to have a negative experience by chasing them with a net, as a result teaching the fish to enter one compartment and not the other.

The fish were divided into two groups, with half being housed with a much larger fish for 24 hours, which was predicted to provide them with a negative experience.

“Murray cod are territorial fish by nature, even known to be cannibals,” Ms Rogers said.

“You would expect them being with another Murray cod of a larger size to be quite unpleasant.

“They were supervised during this time to make sure they were unharmed during this process.”

When returned to their original tank with the five compartments, it was found the fish that were with the larger fish were less likely to enter the middle three compartments.

Ms Rogers said this avoidance of intermediate compartment supports the presence of emotion-like pessimistic states in fish and similar pessimistic responses are seen in humans experiencing depressions, anxiety or chronic stress.

Institute for Land, Water and Society researcher and Associate Professor in Animal Behaviour and Welfare in Albury-Wodonga Dr Raf Freire said the fish’s emotional response to unknown compartments mirrored human behaviour.

“That’s what our emotions do, they affect our judgement,” he said.

“If we are in a bad mood, we judge things negatively and if we are in a good mood, we have a positive interpretation.

“Emotion has an influence on how we judge neutral stimuli and that’s what we showed in the fish.”

Dr Freire said the research, which was funded by CSU Green, helped in understanding how behaviour is controlled in Murray cod is crucial for population growth of the species.

“Animals have to make complex decisions to survive … and our findings suggest fish use an emotion-like process to combine all that information to make a decision,” he said.

“As fisheries are trying to increase populations of native freshwater fish, we can use this to determine how we can make sure that when hatchery-raised fish are released, they have the behaviours to survive.”

The full article is available to read on the PLOS ONE website.

Source: CSU

Featured Image: Leia Rogers