Phosphorous (P) deficiency due to low P availability in fishmeal produced from blue whiting ( Micromesistius poutassou) in feed for under-yearling Atlantic salmon ( Salmo salar) smolt

Abstract

Seawater transferred under-yearling Atlantic salmon (120 g) were fed a practical fishmeal formulated diet containing 57.4% blue whiting fishmeal and providing 15 g kg − 1 total phosphorous (P) in the diet. The basal diet was supplemented with graded dietary levels of inorganic P (0, 3, 6, 9, 12 and 15 g kg − 1 ) to total P levels of 15, 18, 21, 24, 27 and 30 g kg − 1 . Within a feeding period of 12 weeks, classical signs of P deficiency developed in Atlantic salmon fed the P un-supplemented diet containing 15 g kg − 1 total P of natural origin. Deficiency signs included reduced growth and feed efficiency, reduced tissue mineral concentration (P, Ca, Mg, Zn), increased P:Ca ratio in the body, increased condition factor, metabolic disorder as indicated by lipid accumulation and impaired protein utilization, as well as reduced lipid, energy and Zn digestibility. Supplementation of inorganic P-salts in the diet at 3 g kg − 1 (18 g kg − 1 total P) significantly improved the production results with respect to growth and feed efficiency, and restored all other signs of P deficiency in fish. A higher supplementation level of 6 g kg − 1 inorganic P (21 g kg − 1 total P) was required for optimal mineralization in whole body and vertebrae. The highest supplementation levels of 15 g kg − 1 added inorganic P (30 g kg − 1 total P) seemed to increase P excretion and to have slightly negative impacts on growth and bone mineralization. Results suggest that P availability from blue whiting fishmeal is very low (3.2 g kg − 1 ) and inadequate to meet dietary P requirement in rapidly growing under-yearling salmon immediately following seawater transfer, despite high natural P content in the blue whiting fishmeal.