How can we tell if fish have emotions?

The question of animal emotion lies at the heart of concern for animal welfare. Fish are now being used in a medical research in their millions. For our plates, aquaculture and fisheries produce millions of tonnes of fish each year. They are also very popular as pets and in zoos. Fish show surprising intelligence and an ability to feel pain, growing evidence suggests. But do fish have feelings and how could we measure them?

This is a critical question -  to ensure good welfare for fish we need to find out how our experimental, husbandry or fishing activities impact on animals' emotions, and whether refinements to these do indeed improve welfare from the fishes' point of view. We can also benefit ourselves from studying animal emotion so that we better understand, and find ways to treat, widespread human emotional disorders like depression - a leading cause of disability that imposes huge socio-economic costs globally.

Fish, particularly zebrafish, are now extensively used as laboratory animals in a range of medical research (12% of laboratory animals used in the UK in 2012 were fish), including on human emotional disorders. This is because they offer many practical advantages and animal welfare benefits compared to mammals such as rats and mice.  But to ensure fish experience the best possible welfare and give us relevant information for improving human health, we need to better understand their emotions.

Depressed humans make pessimistic judgements - the idiomatic glass half empty. Like humans, several species of mammal including rats and dogs, birds and bees with poor welfare show similarly 'pessimistic' decisions about ambiguous situations while those with better welfare may be more 'optimistic'. These cognitive biases offer new ways to measure animals' emotions, but this has not yet been tried for fish. My current goal as a scientist [about me] is to use this approach to find new measures of emotion in fish, then use these to find ways to improve laboratory zebrafish welfare. You might say I want to ask fish whether the tank is half full or half empty!

Humans as well as fish could benefit from this. Using better measures of emotion in medical research involving fish would help in finding new treatments for diseases like depression or anxiety. It could also allow scientists to use fewer animals overall in developing new drugs because the practical advantages of fish mean potential medicines could be assessed at an earlier stage of the process.

This blog will track my scientific journey into the mind of a fish...