Replacement of dietary macroalgae with corn starch in juvenile sea cucumber Apostichopus japonicus (Selenka)

A 70-day experiment was conducted to investigate the optimal dietary macroalgae and substitute proportion by corn starch in juvenile sea cucumber Apostichopus japonicus. Sea cucumbers were fed by eighteen different diets formulated with one of the three macroalgae including Sargassum muticum, Gracilaria lemaneiformis and Ulva lactuca and six graded levels (0, 50, 100, 200, 300 and 400 g/kg) of corn starch as the replacements for each seaweed. An isotope mixing model indicated that the relative contribution of corn starch to the growth of A.japonicus did not consistently increase, even slightly decreased with increasing dietary corn starch level. The contributions of corn starch to A.japonicus fed by diets containing S.muticum were higher than those fed by diets containing G.lemaneiformis with corresponding corn starch levels or containing U.lactuca at 200-400 g/kg replacement proportions. The growth of A.japonicus first significantly increased and then decreased with increasing corn starch level, regardless of macroalgal species. The corn starch could replace up to 200 g/kg of dietary G.lemaneiformis or U.lactuca, even up to 300 g/kg of S.muticum without affecting growth performance. Based on the polynomial regression model, the replacement of S.muticum with 114 g/kg corn starch was optimal for A.japonicus.