Dietary phosphorus requirement of coho salmon (Oncorhynchus kisutch) alevins cultured in freshwater

A 12-week feeding trial was conducted to evaluate the effects of dietary phosphorus on growth performance, whole-body composition, liver phosphorus metabolism enzyme and digestive enzyme activities of coho salmon (Oncorhynchus kisutch) alevins. Six experimental diets were formulated with graded phosphorus levels of 0.3%, 0.59%, 0.73%, 0.85%, 1.05% and 1.19% respectively. Each diet was fed to triplicate groups of fish (0.36 +/- 0.01 g), which were randomly assigned to 18 tanks (water volume 240-L), with each stocked initially with 50 fish. The specific growth rate (SGR), whole-body and vertebrae phosphorus contents, lipase and amylase were significantly improved with dietary phosphorus level increased from 0.3% to 0.85% (p < .05). The feed conversion rate, alkaline phosphatase and creatine kinase activities were significantly decreased with dietary phosphorus level increased from 0.3% to 0.73% (p < .05). The hepatosomatic index, intestosomatic index, condition factor and whole-body moisture, crude protein, crude lipid and ash were not affected by dietary treatments (p > .05). More accurate information on dietary phosphorus requirement was obtained by cubic curve regression analysis of SGR, whole-body and vertebrae phosphorus contents, which indicated that phosphorus dietary requirement levels for coho salmon alevins were 0.95%, 1.06% and 1.11% respectively.