The phenomenon of tail-biting has created headaches for salmon farmers for many years, and not much was known about its causes until a recent study undertaken by Stirling University and Scottish salmon farming company Loch Duart.
Tail-biting, most common in freshwater salmon farms, occurs when fish chase and bite each other’s dorsal fins, leading to the deterioration the health and quality of affected fish.
Scientists at Loch Duart, led by assistant freshwater manager David Roadknight, determined a variety of factors encourage or ameliorate tail-biting, including low water current, higher stock densities and interruptions to feeding, which make the salmon hungry and aggressive. However, even after those variables had been controlled for, the tail-biting was still occurring, leading to the inclusion of another factor that contributes to tail-biting: boredom.
Tank interiors giving fish bland and uninteresting ambient surroundings were improved with lines of brightly colored plastic balls and dark tarpaulins that gave fish places to hide, according to a press release.
“Hiding is a natural instinct essential to survival for young fish and now they are able to fulfill this. Hiding also gives a measure of protection against ‘bully’ fish – the major biting culprits,” the release said. “The balls are for a slightly different reason. All animals play and salmon are no different. This can lead to behavioral problems with dominant fish nipping the dorsal fins of their tank-mates - a sort of fish tag game with consequences. Once this behavior starts, it is very hard to stop. The balls are points of interest and items for the salmon to play with and around – and they do, breaking [their] pattern of aimless circles.”
Researchers from Stirling University studied the potential breakthrough on site at Loch Duart’s facility and confirmed swim patterns of the salmon and their dorsal fin quality have improved. Stirling University professor of aquatic population health and welfare Jimmy Turnbull said he’s hopeful the study can lead to a large-scale change in the industry’s best practices.
“This is obviously a very small study and you cannot extrapolate too far from it – but the fish in the tanks with enrichment apparently have better fins and this is very promising,” he said.
Loch Duart Managing Director Alban Denton said the work on reducing tail-biting is part of his company’s broader commitment to achieving the best welfare possible for its fish.
“David Roadknight’s innovation has the potential to improve the welfare of salmon in hatcheries significantly,” Denton said. “Good welfare is a key reason why Loch Duart salmon is renowned for its fine taste because we know that welfare and taste are inextricably linked.”
