Requirement of Rainbow Trout for Dietary Phosphorus and Its Relationship to the Amount Discharged in Hatchery Effluents

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Abstract
Fingerling rainbow trout Oncorhynchus mykiss with initial mean weights of 9 g (small fish) and 35 g (large fish) were fed diets adequate in all known nutrients except phosphorus (P). In two experiments, triplicate lots of rainbow trout were fed basal diets containing either 0.14 or 0.41% non-phytin P, with or without graded levels of supplemental P. Deficiency of P reduced growth, feed efficiency (weight gained/weight fed), bone ash, and whole-body ash contents. The requirement for non-phytin P by small trout for maximum growth and feed efficiency was not more than 0.41% of diet: The requirement by large trout was between 0.34 and 0.54% of diet. The requirement of non-phytin P for maximum bone ash development was about 0.51% of diet for small trout and more than 0.54% for large trout. Whole-body phosphorus content of small trout suggested a requirement above 0.51% but not more than 0.61% non-phytin phosphorus. Although an effect of size of trout on the requirement was not clearly demonstrated, th...

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