The body clocks of rainbow trout shape daily rhythms of their immune system and the beneficial microorganisms that inhabit their skin, according to new research from a team including academics from Aberystwyth University.

Keeping fish under constant light – often used by fish farms to enhance growth or control reproduction – disrupts these daily rhythms and leads to increased susceptibility to parasites.

This work by researchers at Aberystwyth, Bangor, and Cardiff universities published in the journal Microbiome, demonstrates how important understanding the “chronobiology” of animals is for maintaining their health.

One of the co-authors of the report, Dr David Wilcockson from Aberystwyth University’s Institute of Biological, Environmental and Rural Sciences, said: “This is the first study to look at the daily rhythms of fish microbiomes.

“The findings suggest that current farming techniques could be having an unintended impact on fish health.”

Dr Amy Ellison, a lecturer at Bangor University’s School of Natural Sciences and lead author of the research, added: “Rainbow trout have daily or ‘circadian’ rhythms in their immune activity and these rhythms appear to shift the composition of the microbial communities which live on their skin over day-night cycles.

“These fish skin ‘microbiomes’ are a first line of defence against invading parasites and pathogens, so this could be very important for their health.”

The study is part of a Biotechnology and Biological Sciences Research Council Discovery fellowship funded project to investigate the chronobiology of fish, their parasites and microbiomes.