Keeping fish under constant light, often used by fish farms to enhance growth or control reproduction, disrupts the daily rhythms and leads to increased susceptibility to parasites, researchers at Bangor, Cardiff and Aberystwyth Universities, found. 

Lead author Amy Ellison, a lecturer at Bangor University’s School of Natural Sciences, said that “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 defense 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. When infected with parasitic skin lice, fish under constant light were less able to rid themselves of infection,” Ellison said. 

“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,” said co-author Prof. Jo Cable from Cardiff University School of Biosciences.

“Chronotherapies, the appropriate daily timing of vaccines and other treatments, is beginning to revolutionize human medicine. But this is yet to be applied to farmed animals. Our study raises the possibility that similar approaches could be used to help maintain fish health and welfare on farms,” said co-author David Wilcockson from Aberystwyth University Institute of Biological, Environmental and Rural Sciences.

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

Check out the study here.