Emotional states in animals are still a matter of debate for biologists. Now, for the first time, Portuguese researchers have demonstrated that fish have emotional states triggered by their environment.

Fish (depicted here: Sparus aurata) turned out to be more complex than we thought. Image credits: Werner – Histoire naturelle des poissons.

Evaluating emotional states is not easy in humans, and we have the ability to verbalize it. In animals, it’s an incredibly challenging task. There’s no straightforward way to check if an animal is feeling an emotion — so scientists had to turn to an indirect approach. They know that emotions are accompanied by behavioral, physiologic, neurologic and genetic changes, so if they can see these changes, they can infer an emotion.

Using this approach, previous studies have demonstrated such emotions in primates and other mammals, though it’s not clear if these feelings are conscious or not. Now, researchers wanted to investigate if “simpler” animals like fish go through a similar process.

Whether or not fish have emotions and feel pain used to be a matter of heated debate. Culum Brown, a professor at Macquarie University in Sydney, Australia, previously showed that not only do fish feel pain, but they can also multitask and have cultural traditions. But how do you demonstrate that they have feelings?

The Portuguese biologists trained fish (sea bream) under both favorable and adverse conditions; these conditions were expected to trigger an emotional state. They then analyzed this emotional response by measuring the levels of cortisol, a stress hormone, and seeing what brain areas become activated. Researchers also tracked fish interaction and overall behavior to assess their response and then backtrace it to emotional states.

“Our data supports the occurrence of emotion-like states in fish that are regulated by the individual’s perception of environmental stimuli, the study reads.”

They showed not only that fish do get feelings, but this study might give us a better understanding of how emotions came to be in the first place. Since fish represent a different evolutionary branch than tetrapods, this might indicate that emotions emerged before the two groups separated. Alternatively, it could be a case of convergent evolution.

“This is the first time that is shown that fish can trigger physiologic and neuromolecular responses in the central nervous system in response to emotional stimuli based on the significance that that stimulus has for the fish”, says study author Rui Oliveira. The researcher explains that “the occurrence of the cognitive assessment of an emotional stimulus in fish means that that this cognitive capacity may have ‘computational’ requirements simpler than what has been considered until now, and may have evolved around 375 million years ago.”

Journal Reference: M. Cerqueira et al. Cognitive appraisal of environmental stimuli induces emotion-like states in fish, Scientific Reports (2017). DOI: 10.1038/s41598-017-13173-x