Health assessment of the cleaner fish ballan wrasse Labrus bergylta from the British south-west coast

Abstract

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. Wildcaught ballan wrasse (n = 75) from coastal populations of 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 hlyA ch 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.

Cosmopolitan Distribution of Endozoicomonas-Like Organisms and Other Intracellular Microcolonies of Bacteria Causing Infection in Marine Mollusks

“…A pathogenic M. mobile was originally isolated from the gills of a freshwater fish, the tench Tinca tinca L, showing a characteristic fast gliding motion (Kirchhoff and Rosengarten, 1984). Other mycoplasmas have been reported historically from fish-derived cell lines (Emerson et al, 1979), and fish tissues, in particular, Acholeplasma laidlawii considered to be a non-pathogenic microorganism (McMurtrie et al, 2019). In the present study, all the samples with mycoplasma sequences showed co-infections with Endozoicomonadaceae.…”

Cleaner fish in aquaculture: review on diseases and vaccination

“…damselae has been reported from diseased rainbow trout during warm summer periods in Denmark (Pedersen et al, 1997), and Atlantic salmon have demonstrated susceptibility to disease under experimental conditions (Austin et al, 1997). Further work is needed however, to investigate its potential risks at cooler northern European climate conditions (McMurtrie et al, 2019).…”

“…Systemic infection with Photobacterium damselae subsp. damselae (Pdd) (formerly Vibrio damselae ) was recently reported from a single wild‐caught ballan wrasse from the British south‐west coast during the warmest average water temperatures that year (McMurtrie et al, 2019). Photobacteriosis is a devastating fish disease in warm and temperate aquaculture locations, where a closely related subspecies, Photobacterium damselae subsp.…”

“…The species has of yet not been identified, but have been reported to resemble Uronema marinum , which have been observed in several marine fish species (Piazzon et al, 2013; Scholz et al, 2018a). Other ciliates have been reported from the gills of wrasse without any apparent damage to the tissue, such as the scuticociliate Pseudocohnilembus persalinus , and Cryptocaryon ‐like ciliates (McMurtrie et al, 2019). The species C .…”

Mind the Depth: The Vertical Dimension of a Small‐Scale Coastal Fishery Shapes Selection on Species, Size, and Sex in Wrasses

“…In addition, concerns have been raised regarding bycatch of other valued species, such as brown crab Cancer pagurus , Atlantic Cod Gadus morhua , and European lobster Homarus gammarus (Grefsrud et al 2018:166–174). Since the wrasse fishery also has recently expanded in the southern regions of the UK and in Scotland (Riley et al 2017; McMurtrie et al 2019), there is an increasing need for better knowledge of how this fishery impacts target species and bycatch and a need to develop methods for accurate and efficient monitoring of the stocks.…”