Effects of dietary carbohydrate on weight gain and gonad production in small sea urchins, Lytechinus variegatus

In experiment 1, juvenile sea urchins (n=80, 0.088 +/- 0.001g wet weight and 5.72 +/- 0.04mm diameter) were held individually and fed adlibitum one of three semi-purified formulated diets (n=16 individuals treatment(-1)). In the diets, protein was held constant (310gkg(-1) dry, as fed) and carbohydrate level varied (190, 260, or 380gkg(-1) dry, as fed). Wet weights were measured every 2weeks. Total wet weight gain was inversely proportional to dietary carbohydrate level and energy content of the respective diet. In experiment 2, sea urchins (5.60 +/- 0.48g wet weight, n=40) fed 190gkg(-1) carbohydrate consumed significantly more dry feed than those fed 260gkg(-1), but not more than those fed 380gkg(-1) carbohydrate. Based on differential feed intake rates, sea urchins that consumed more feed also consumed higher levels of protein and had the highest weight gain. Consequently, protein content and/or protein: energy ratio may be important in determining feed utilization and growth among sea urchins in this study. The average digestible energy intake was approximately 70kcalkg(-1) body weight day(-1), suggesting daily caloric intake of juvenile Lytechinus variegatus is lower than in shrimp and fish.