Requirement of chum salmon held in freshwater for dietary phosphorus

Chum salmon, Oncorhynchus keta, held in freshwater and weighing an average of 1.5g, were fed purified diets containing different amounts of calcium and phosphorus for 7 weeks. The growth rate correlated positively with dietary phosphorus levels but not with calcium levels. Feeding a low-phosphorus diet resulted in reduced growth, low feed conversion and insufficient development of the bones. Dietary phosphorus levels greatly affected the ash, calcium and phosphorus contents of the bones. The available phosphorus level in a diet producing the maximal growth and the normal development of bones was found to be 0.5-0.6%, when the rearing water contained an adequate amount of calcium. The results obtained with fish fed diets containing white fish meal as a protein source also demonstrated that the availability to chum salmon of the phosphorus contained in the fish meal was relatively high. Thus the supplementation of the diets containing this fish meal with primary sodium phosphate resulted in no acceleration of the growth response of the fish.