Utilization of α-starch in ayu, Plecoglossus altivelis, relating to growth and body composition

Summary To examine the possibility of dietary α-starch in reducing feed costs in a practical diet, α-starch was supplemented at 10, 20, 30 and 40% in a composed diet having the same protein level. The four diets were fed to ayu, Plecoglossus altivelis (initial weight 9.1 g) for 43 days. Growth and feed efficiency increased with the supplement, with values highest in the 30–40%α-starch diet. The level of dietary α-starch did not affect the proximate muscle composition; although the hepatosomatic index was not affected, liver glycogen increased with increasing dietary α-starch. The dietary α-starch did not influence evacuation time from the gut, and was well digested through passage in the gut, mainly between the stomach and the anterior part of the intestine. Ayu have an ability to adapt their metabolism to high dietary α-starch, and can digest 40% or more in a composed diet. Although the muscle lipid content did not change, the fatty acid composition was influenced by dietary starch. With the elevation of dietary starch, a decrease of C18:2n-6 and an increase of C22:6n-3 occurred. These results indicate that at least 40%α-starch can be used in practical diets for ayu.