Supplementation of dietary minerals during the early seawater phase increase vertebral strength and reduce the prevalence of vertebral deformities in fast-growing under-yearling Atlantic salmon (Salmo salarL.) smolt

Abstract

An earlier study demonstrated that under-yearling (0+) Atlantic salmon (Salmo salar L.) smolt had a lower vertebral mineral content and mechanical strength and higher prevalence of vertebral deformities than 1+ smolt during the early seawater (SW) phase. The present study aimed to examine if commercial extruded high-energy diets need to be supplemented additional minerals for proper bone mineralization and prevention of bone deformities in fast growing 0 + smolts. We studied vertebral morphology with radiology, and bone mineral content and mechanical strength in 60 g 0+ smolt fed diets with a normal (NM) or elevated (HM) bone mineral (P and Ca) contents from SW transfer (week 0) until 10 times weight increase at week 17. Thereafter, both groups were fed a commercial diet until a mean slaughter weight of 4100 g after 57 week. There were no differences in body weight and length between the dietary groups during the study, while the condition factor differed significantly at the final sampling (NM 1.40; HM 1.29). The most common bone deformity observed was compressions in the tail region of the vertebral column. Lower incidences of vertebral deformities (percent individuals with one or more deformed vertebrae) was observed in the HM group in week 17 (HM 20%; NM 47%) and week 57 (HM 37%; NM 73%), also reflected by higher vertebral length/dorso-ventral diameter ratio in weeks 17 (HM 0.99; MN 0.92) and 57 (HM 0.97; NM 0.88). The HM group had significantly higher vertebral mineral content (HM 550 g kg−1; NM 480 g kg−1) and mechanical strength (HM 9050 g mm−1; NM 4600 g mm−1) than the NM group after 8 week feeding. Plasma levels of Ca, P and D-vitamin metabolites recorded in week 8 reflected changes in P homeostasis, but could not explain the preventive effect of the HM diet on development of bone deformities. The results suggest that elevated dietary mineral content during the early SW phase may reduce the prevalence of vertebral deformities in fast growing 0 + salmon smolts.