National Research Council of Canada. NRC Institute for Marine Biosciences
National Research Council of Canada. Aquatic and Crop Resource Development
bone resorption; histomorphometry; marine fish; osteoblasts; osteoclasts; phosphorus deficiency
Phosphorus (P) deficiency in the diet of teleost fishes decreases the mineral content of bone. The present study investigated the changes in the microanatomy and metabolism of acellular-boned juvenile haddock (Melanogrammus aeglefinus L.) in relation to the P content of the diet and to determine whether bone deformities develop in association with P deficiency. Fish were fed diets containing low (0.42% diet), optimum (1.02% diet) and excess (1.42% diet) levels of P for 8 and 20 weeks. At the end of two experimental periods, fish were subjected to gross examination, x-rayed, and the mineral content of the plasma and the vertebrae was measured. The vertebrae were also subjected to histological, histomorphometric and enzyme histochemical examinations to determine the level of bone formation and resorption. A P-deficient diet caused a delay in bone mineralization. In contrast, excess P in the diet increased matrix deposition and resulted in accelerated mineralization. Counting the numbers of osteoblasts and osteoclasts, and measuring the mineralized bone and the non-mineralized bone suggest that P deficiency in haddock initially increases bone resorption and subsequently decreases bone mineralization followed by a decrease in bone formation. The increase of the number of osteoclasts in P-deficient animals suggests that osteoclasts could be involved in P homeostasis. In the same fish group low bone mineral and deformed bones observed on x-rays, could be the result of a decrease in mineralization of the bone matrix.