The aetiology of spinal deformity in Atlantic salmon, Salmo salar L.: influence of different commercial diets on the incidence and severity of the preclinical condition in salmon parr under two contrasting husbandry regimes

• Published in: Journal of Fish Diseases
• Main Authors: Sullivan, M, Reid, S W J, Ternent, H, Manchester, N J, Roberts, R J, Stone, D A J, Hardy, R W
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2007
• Subjects: Atlantic salmon; Salmo salar
• Online Access: http://dx.doi.org/10.1111/j.1365-2761.2007.00890.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1365-2761.2007.00890.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2761.2007.00890.x

Abstract A large‐scale trial of the effect of different commercial diets on the incidence of preclinical spinal deformation, as assessed by radiography, and the influence of two contrasting rearing systems was carried out. Two sets of three populations of Atlantic salmon, each of 20 000 first feeding fry of identical hatchery origin, created from equal numbers of eggs from 15 different families, were reared under commercial conditions on two different farms. Three commercial (closed formula) extruded fish meal‐based diets were used in this study (diets A, B & C). Each diet was fed to one population of 20 000 fish at each site. Fish were fed a percentage of their body weight per day, with feeding rates set at commercial levels, based on water temperature, day length and fish biomass. Additional hand feeding was used to ensure satiation in all tanks. Fish in each tank were bulk‐weighed and counted at the beginning and at 2‐week intervals throughout the study. The fish were grown for 30 weeks. In addition, phosphorus (P) digestibility was evaluated by in‐feed absorption testing in rainbow trout. The morphology of the radiographic lesions conformed to those described previously. Statistical analysis using multivariate regression analysis showed that date of sampling, site and diet were all statistically significant ( P < 0.001) on univariable analysis. Farm A had significantly more affected fish than farm B ( P < 0.001), which may have been attributable to variation in dissolved oxygen levels. The available dietary P levels were low in each diet. The number of fish affected in the group of fish being fed diet B was significantly lower than in the groups being fed diets A or C ( P < 0.001). It appears most likely that the occurrence of preclinical radiographically apparent defects in parr which are believed to lead to the condition known as ‘spinal deformity’ is predominantly caused by a deficiency of available dietary P in first‐feeding fry. The availability of dietary P may also vary considerably ...