Macroalgal substitution effect in diet on growth, body composition, and stress resistance of juvenile sea cucumber (Apostichopus japonicus) subjected to air and low salinity exposures

Effect of various macroalgae substitution for Sargassum thunbergii in diet on growth, body composition, and survival of sea cucumber (Apostichopus japonicus) subjected to air and low salinity exposures was determined. Nine hundred juvenile sea cucumber were distributed into 18 tanks (50 sea cucumber per tank). Six experimental diets were prepared. Sargassum thunbergii was included in the control (Con) diet. The macroalgae Sargassum horneri, Undaria pinnatifida, Saccharina japonica, Ulva australis, and combined U. pinnatifida and S. japonica were included to replace S. thunbergii in the Con diet, referred to as the SH, UA, UP, SJ, and combined diets, respectively. All diets were assigned to triplicate groups of sea cucumber. Sea cucumbers were fed daily for 8 weeks. After the 8-week feeding trial, sea cucumbers were subjected to 30-h air and 12-h low salinity at 10 psu exposures. Weight gain and specific growth rate of sea cucumber fed the Con, SH, and UA diets were significantly greater than those of sea cucumber fed the UP, SJ, and combined diets. The chemical composition of the whole sea cucumber, except for moisture content, was not affected by the experimental diets. No difference in survival of sea cucumber fed all experimental diets was observed at the end of 4-day post observation period after the 30-h air and 12-h low salinity exposures. In conclusion, S. thunbergii can be substituted with either S. horneri or U. australis in sea cucumber feed without retarding growth and stress resistance against air and low salinity exposures.