Phosphorus Deficiency in Rainbow Trout Fed a Diet Containing Deboned Fillet Scrap

Whole Pacific hake (Merluccius productus) and hake fillet scrap were ground, heated to accelerate enzymatic hydrolysis, and acidified to prevent microbial degradation. Half of the fillet scrap was screened to reduce the bone content of the product. After 10 d of storage, the liquefied products were combined with feather meal and dried. The dried products replaced fish meal in practical diets, which were fed to rainbow trout (Salmo gairdneri) for 22 weeks. Significant reductions in plasma phosphorus and whole-body and vertebral calcium, phosphorus, and magnesium concentrations were found in rainbow trout fed the diet containing the deboned fillet scrap, while fish fed a phosphorus-supplemented diet had levels similar to fish fed the diets containing whole fish. Plasma alkaline phosphatase activity was unaffected by diet. Rainbow trout fed a diet containing unscreened fillet scrap were similar in all respects to fish fed a diet containing whole fish. This study shows that the high dietary ash present in products made from fillet scrap is not detrimental in trout diets containing recommended levels of trace elements, such as zinc, and that screening to reduce the bone content of the fillet scrap lowers the phosphorus content below required dietary levels.