The requirement of dietary phosphorus was investigated in two age groups of redlip mullet, Liza hematochieln. Fish with initial mean weights 3.8 g (zero year-old) and 26.5 g (one yearold) were fed on purified diets containing varying dietary levels of phosphorus (0.3 to 1.1 %). Results from two studies indicated that the available phosphorus requirement of redlip mullet is approximately 0.7%. In both experiments weight gain together with feed efficiency were maximal in fish fed diets containing 0.6-0.7% dietary phosphorus, but further elevation above this level did not result in a better growth. In a zero year-old fish, it was found that the decrease in the dietary P level resulted in the increase in the lipid, and the decrease in Ca, P and crude ash contents of vertebrae. However, no such effect was observed for the one year-old fish. In all groups both serum and bone Ca/P ratio performed values of 3: 1 and 1: 1 in zero and one yearold redlip mullet, respectively, suggesting a predominancy of Ca content in body tissues at early stages. Hence. the change in balance between Ca and P is an age dependent.
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