Effects of size and temperature on growth and feed conversion of juvenile green sea urchin (Strongylocentrotus droebachiensis)

Abstract

Juvenile green sea urchins, Strongylocentrotus droebachiensis ranging in size from 0.1 to 30g were held in individual compartments at four constant temperatures (6, 10, 12 and 14°C) (n=54 per temperature treatment) for a period of 100days. Growth, survival, feed intake and feed conversion ratio (FCR) of the urchins were monitored during this period. There was no mortality throughout the experimental period. The growth of the urchins was significantly affected by seawater temperature with the group held at 6°C having a significantly lower specific growth rate (SGR) (% body growth per day) than the urchins held in any other temperature treatment. There were no significant differences in specific growth rate (SGR) between the urchins held in the other three temperature groups (10, 12 and 14°C).Feed conversion ratio (FCR) (grams of feed used to increase the body wet weight by one gram) was also significantly affected by temperature with urchins held at 10°C having significantly lower FCR values (2.2±0.7) than those held in the 6°C temperature group (3.39±1.6). These in turn were significantly lower than those in the 12°C temperature groups (7.02±1.5) and these were significantly lower than those in the 14°C temperature group (8.8±2.2). Within the temperature groups, FCR was size dependent and decreased with increasing urchin size.In conclusion, the present study shows that a rearing temperature of 10°C appears to be optimal for juvenile green sea urchins in the size range of 0.1 to 30g when both feed conversion and growth rate are taken into account.