Disrupting the body clocks of fish could be bad for their health

The findings of a new study, co-led by Prof Jo Cable, could have implications for the farmed fish industry

New research reveals the body clocks of rainbow trout shape daily rhythms of their immune system and the microorganisms that inhabit their skin. 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.

Published in the journal Microbiome, the work by researchers at Cardiff, Bangor and Aberystwyth Universities, demonstrates how important understanding the 'chronobiology' of animals is for maintaining their health.

Co-author Prof Jo Cable, Chair of Parasitology and Head of the Organisms and Environment Division, states:

“This is the first study to look at the daily rhythms of fish microbiomes. There is increasing interest in the aquaculture industry to maintain ‘healthy’ microbiomes in farmed fish to improve their disease resistance. However, current farming practices could have unintended consequences for fish health.”

Lead author Dr Amy Ellison, lecturer at Bangor University’s School of Natural Sciences explains:

“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.”

“We found that raising fish under continuous light severely impacted the timings of their immune system and microbiomes. Worryingly, when infected with parasitic skin lice, fish under constant light were less able to rid themselves of infection.”

Skin lice are a widespread problem in aquaculture. The research also revealed that lice infections significantly alter trout skin microbial communities, increasing the abundance of pathogenic bacteria.

Co-author Dr David Wilcockson from Aberystwyth University Institute of Biological, Environmental and Rural Sciences added:

“Chronotherapies – the appropriate daily timing of vaccines and other treatments - is beginning to revolutionise human medicine. But this is yet to be applied to farmed animals. Our study raises the possibility similar approaches could be used to help maintain fish health and welfare on farms.”

The study is part of a BBSRC Discovery fellowship funded project to investigate the chronobiology of fish, their parasites and microbiomes.