Skeletal deformities in wild and farmed cleaner fish species used in Atlantic salmon Salmo salar aquaculture

Abstract

As a first attempt to assess bone health in cleaner fish production, wild and cultured ballan wrasse Labrus bergylta and lumpfish Cyclopterus lumpus were examined by radiology. In C. lumpus, wild fish (57%) had more vertebra deformities (≥1 deformed vertebrae) than cultured fish (2–16%). One wild C. lumpus had lordosis and another was missing the tail fin. In L. bergylta, wild fish (11%) had fewer vertebra deformities than cultured individuals (78–91%). Among the cultured L. bergylta, 17–53% of the fish had severe vertebra deformities (≥6 deformed vertebrae) with two predominate sites of location, one between vertebra 4 and 10 (S1) in the trunk, and one between 19 and 26 (S2) in the tail. Fusions dominated S1, while compressions dominated S2. Although wild L. bergylta had a low vertebra deformity level, 83% had calluses and 14% had fractures in haemal/neural spines and/or ribs. The site‐specific appearance and pathology of fracture and callus in wild L. bergylta suggests these are induced by chronic mechanical stress, and a possible pathogenesis for fish hyperostosis is presented based on this notion. In conclusion, good bone health was documented in cultured C. lumpus, but cultured L. bergylta suffered poor bone health. How this affects survival, growth, swimming abilities and welfare in cultured wrasse should be further investigated. Significance Statement Skeletal deformities were studied in ballan wrasse and lumpfish of both wild and cultured origin for the first time to identify potential welfare issues when deploying them as cleaner fish in salmon sea cages. While cultured lumpfish showed good bone health, cultured wrasse had a high occurrence of vertebra deformities, which is expected to impact lice eating efficiency and animal welfare negatively. These deformities are most likely induced early in development.

Monsters with a shortened vertebral column: A population phenomenon in radiating fish Labeobarbus (Cyprinidae)

“…To the best of our knowledge, apart from the Genale Labeobarbus , the similar situations are described for only two other fish species, Atlantic cod Gadus morhua from the Elbe estuary and German Wadden Sea [ 85 , 86 – 88 ] and Arctic char Salvelinus alpinus from Transbaikalian Lake Dzhelo [ 89 ]. The high prevalence of vertebral column deformities was recently reported in a wild population of lumpfish Cyclopterus lumpus L. 1758 from Masfjorden, Norway [ 137 ], but changes of the body form and temporal stability of the abnormal phenotypes are not evident in the latter species.…”

Cleaner fish in aquaculture: review on diseases and vaccination

“…Jaw and spinal deformities have also been observed but not sufficiently documented (Brooker et al, 2018;Scholz et al, 2018a). A recent study observed high occurrences of vertebra deformities in cultured wrasse, while, surprisingly, the observed deformity rate was lower in cultured lumpfish (Fjelldal et al, 2020). Spinal deformities have also been reported from farmed Atlantic salmon, with several environmental and nutritional conditions being potential risk factors (Fjelldal et al, 2012).…”

A boost for fish skeletal research

“…Another recent source of knowledge about fish skeletal biology is research on farmed fish. Animal welfare, healthy growth and the quality of the products stimulate these studies (Fjelldal et al ., 2020, this volume). Species in focus are full‐sized teleosts.…”