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.
Highlights
Infestation by the sea lice Lepeophtheirus salmonis K. 1837 and to lesser extent Caligus elongatus N. 1832 are major challenges in sea cage based aquaculture of salmonids in the northern hemisphere while species such as Caligus teres W. 1905 and C. rogercresseyi B. & B. 2000 pester the southern hemisphere (Costello, 2009; Abolofia et al, 2017; Brooker et al, 2018)
Screening different production batches of cultured fish and wild fish showed low and high vertebra deformity rates in cultured C. lumpus and L. bergylta, respectively, while among wild fish, C. lumpus had more deformities compared to L. bergylta
To our surprise, wild L. bergylta had a high occurrence of neural/haemal spine and rib pathologies, and lack of tail fin and lordosis were recorded in wild C. lumpus
Summary
Infestation by the sea lice Lepeophtheirus salmonis K. 1837 and to lesser extent Caligus elongatus N. 1832 are major challenges in sea cage based aquaculture of salmonids in the northern hemisphere while species such as Caligus teres W. 1905 and C. rogercresseyi B. & B. 2000 pester the southern hemisphere (Costello, 2009; Abolofia et al, 2017; Brooker et al, 2018). Infestation by the sea lice Lepeophtheirus salmonis K. 1832 are major challenges in sea cage based aquaculture of salmonids in the northern hemisphere while species such as Caligus teres W. As an alternative to other delousing methods, deployment of cleaner fish (Bjordal, 1990) in sea cages is growing in popularity as they have been found to efficiently remove L. salmonis from S. salar (Imsland et al, 2018a; Leclercq et al, 2014; Liu & Bjelland, 2014). Only wild wrasse species were deployed (Gonzalez & de Boer, 2017; Treasurer, 2002), but cultured L. bergylta (Skiftesvik et al, 2013) and C. lumpus (Imsland et al, 2014a) are widely used
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