Wild-caught ballan wrasse Labrus bergylta are translocated en masse from the British south-west coast to Scotland for use as cleaner fish to tackle Atlantic salmon Salmo salar sea lice infestations; however, very little is known about the background health status of this species. This is the first health assessment of wild ballan wrasse from the British south-west. Wild-caught ballan wrasse (n = 75) from coastal populations off Dorset and Cornwall were subjected to a full health screen for viral, bacterial and parasitic infections and associated pathology. A range of metazoan and protozoan parasites were observed in histological sections, including copepods (sea lice Caligus centrodonti), nematodes, cestodes, digenean metacercariae, Cryptocaryon-like ciliates and an intestinal coccidian (Eimeria sp.) observed in 26.6% of the samples. The mycoplasma Acholeplasma laidlawii was associated with cytopathic effect in cell culture inoculated with tissue homogenates. The opportunistic pathogen Photobacterium damselae damselae was isolated from a single fish with a systemic infection. The isolate was confirmed to possess the virulence factors hlyAch and plpV, previously associated with cell toxicity and pathogenicity to fish. There are no immediate concerns for the continued mass translation of ballan wrasse, however careful monitoring of the population is recommended.
Keywords: Ballan wrasse; Caligus centrodonti; Cleaner fish; Eimeria · Coccidian; Photobacterium damselae damselae; Salmon aquaculture.