Dietary vitamin A requirements of coho salmon Oncorhynchus kisutch (Walbaum, 1792) post-smolts

Abstract

A ten-week feeding trail was conducted to determine the dietary vitamin A (VA) requirement of coho salmon Oncorhynchus kisutch (Walbaum, 1792) post-smolts by formulating seven experimental diets containing graded VA levels of 367, 1060, 1823, 3482, 6715, 9984 and 22,935 IU/kg, respectively. Each diet was fed to triplicate groups of fish with the initial mean body weight of 185.86 ± 1.14 g. Stocked as groups of 10 individuals per cage (water volume 1000-L), fish were fed three times daily. After the feeding trail, the orthogonal polynomial contrasts showed that the specific growth rate (SGR) was linearly, quadratically and cubically increased with increasing dietary VA levels (P < .05). No significant differences were observed for hepatosomatic index (HSI), intestosomatic index (ISI), condition factor (CF) and muscle composition among dietary groups (P > .05). The muscle moisture, ash and crude protein were not significantly affected (P > .05), whereas the crude lipid was cubically affected (P < .05) by graded dietary VA levels. Serum alkaline phosphatase (AKP) activity and albumin (ALB) content were linearly, quadratically and cubically increased, whereas the serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities were linearly, quadratically and cubically decreased with increasing dietary VA levels (P < .05). The increasing VA levels led to significantly linear, quadratic and cubic increase of hepatic SOD, CAT activities and serum SOD activity, and quadratic and cubic increase of serum T-AOC activity (P < .05). Increasing dietary VA levels quadratically and cubically decreased the hepatic MDA content (P < .05). The cubic regression analysis based on SGR indicated that the optimal dietary VA requirement was estimated to be 6422 IU/kg for coho salmon post-smolts.