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 ± 0.001 g wet weight and 5.72 ± 0.04 mm diameter) were held individually and fed ad libitum one of three semi‐purified formulated diets (n = 16 individuals treatment−1). In the diets, protein was held constant (310 g kg−1 dry, as fed) and carbohydrate level varied (190, 260, or 380 g kg−1 dry, as fed). Wet weights were measured every 2 weeks. 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 ± 0.48 g wet weight, n = 40) fed 190 g kg−1 carbohydrate consumed significantly more dry feed than those fed 260 g kg−1, but not more than those fed 380 g kg−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 70 kcal kg−1 body weight day−1, suggesting daily caloric intake of juvenile Lytechinus variegatus is lower than in shrimp and fish.