Effects of temperature and season on gonad growth and feed intake in the green sea urchin ( Strongylocentrotus droebachiensis)

The effects of water temperature and season on feed intake and gonad growth of green sea urchin Strongylocentrotus droebachiensis were evaluated. Animals were tested at six temperatures (4, 6, 8, 10, 12, and 14 °C) in summer (July–September) and in winter (November–January). Sea urchins (64.5 ± 3.4 g mean wet body weight ± S.D.) were held individually in square chambers and fed ad libitum a formulated moist feed. Gonad index (GI), feed intake (FI), and feed conversion ratios (FCR) were measured. There was a significant increase in GI for all treatments during the summer trial, and sea urchins held at 6 °C had a significantly larger GI compared to those held at 4 °C ( P < 0.05). There was no significant difference in GI between sea urchins held at 10, 12 and 14 °C, and they had a significantly higher GI compared to the lower temperature groups. In the winter trial sea urchins held at 8 °C displayed a significant higher GI compared with the other temperatures. There was a significant and linear increase in FI with increasing temperature both during summer and winter. Thus, FI in the summer (S) and winter (W) trials increased from initial 0.34 (S) and 0.26 (W) (g/urchin per day) at 4 °C, to 0.71 (S) and 0.93 (W) (g/urchin per day) at 14 °C. In summer, sea urchins held at 12 °C had a significantly lower FCR (3.3) compared to animals held at 8 °C (FCR = 4.0). The situation was reversed in winter, where sea urchins displayed the lower FCR (3.7) at 8 °C than those held at 12 °C (FCR = 6.0). Overall, our findings suggest that optimum gonad growth of adult green sea urchins is achieved at higher temperatures in summer than in winter.