Fish Farmer December 2021

Cleaner fish

Lumpfish with

personality Profiling the behaviour of individual fish gives a clue as to why some are better at tackling sea lice than others BY BEN WHITTAKER

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UMPFISH are deployed into salmon farms to help control outbreaks of sea lice, but just how effec�ve these cleaner fish are in preven�ng parasites from infec�ng salmon is a ma�er of ongoing debate. While research has found salmon from cages stocked with lumpfish have infec�on rates 60–100% �mes lower than salmon from cages without lumpfish, dietary analysis has revealed that the vast majority of lumpfish in cages do not eat sea lice. Furthermore, recent reviews have cri�cised the high level of varia�on in parasite control between farms stocked with cleaner fish and note that behavioural interac�ons between lumpfish and salmon are very rarely documented. Understanding this high varia�on in cleaning behaviour may help unlock the full poten�al of lumpfish as cleaner fish, leading to more sustainable and efficient methods of controlling sea lice in aquaculture. There are many reasons why some lumpfish might be be�er suited to cleaning salmon than others. Gene�c background, health and welfare, and the environment in which fish are raised are all thought to contribute towards the behaviour of cleaner fish in farms. However, differences in the psychology of individuals may be an overlooked factor influencing varia�on in cleaner fish performance. Researchers from the Centre for Sustainable Aqua�c Research at Swansea University developed a series of behavioural tests to measure personality differences across a cohort of lumpfish. This included tests to record ac�vity levels, how individuals coped with stress, their willingness to take risks and aggression levels, and to compare how social each individual was within the cohort. Tests were repeated twice to check that behavioural responses were consistent and the scores were then used to build an individual personality profile for each lumpfish.

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The lumpfish were then introduced into a tank containing 10 Atlan�c salmon smolts and an observer watched to record how the two species interacted. These interac�ons included co-opera�ve behaviours that would be beneficial for cleaning in a farm environment, such as lumpfish moving closer to visually inspect salmon. Antagonis�c behaviours were also recorded to give context on interac�ons that are not desirable in farms – for example, lumpfish causing salmon to flee. The results showed that a majority of lumpfish ignored salmon. However, individuals that scored higher for “bold and non-aggressive” personality traits spent longer �me periods engaging in co-opera�ve behaviours, while individuals that scored higher for “ac�ve and social” personality traits displayed more antagonis�c behaviour. This suggests that the individual personality of a lumpfish affects how it will interact with salmon, and therefore how effec�ve it will be at removing sea lice. These findings may account for the high varia�on detected by previous studies in sea lice consump�on and cleaning efficiency of lumpfish.

Above: Ben Whi�aker Below: Lumpfish at CSAR Opposite: Novel lumpfish test, CSAR

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09/12/2021 16:09:36