The effect of continuous and intermittent feeding regimes on survival and somatic and gonadal growths of the sea urchin, Strongylocentrotus droebachiensis

A series of experiments were undertaken to determine the effects of continuous (fed weekly) and intermittent (1 week fed/starve; 2 week fed/starve; 4 week fed/starve) feeding regimes on three size classes of Strongylocentrotus droebachiensis (initial average size: SC1, 4.1 mm; SC2, 17.5 mm; SC3, 38.4 mm) fed a manufactured sea urchin diet. In the continuous feed treatment, urchins were fed once per week ad libitum so feed was always available. In the intermittent feed treatments, urchins were fed ad libitum during the 'feed' period and all feed was removed during the 'starve' period. The experiments ran for either 9 months (SC1) or 12 months (SC2 and SC3). The feed treatments had no effect on sea urchin survival (100% regardless of size class or treatment) over the experimental period. The urchins fed weekly had the highest absolute growth in each size class but the differences were more apparent in the small size class (SC1). The 1 week fed/starve treatment had the lowest FCR values in SC1 and SC2 but there was no significant difference between feed treatments in SC3. Urchins in SC1 and SC2 fed weekly had higher GI values than the other feed treatments but in the large size class (SC3) there were no differences in the GI value at the conclusion of the experiment regardless of the feed treatment. The only difference in the reproductive stage of the urchins at the conclusion of the experiments (between feed treatments) was in the medium size class where urchin fed the 4 week fed/starve treatment had a higher percentage of animals (50%) in Stage 3 than the other feed treatments (30%). This study shows that extended periods (up to 4 weeks) of intermittent feeding had a limited effect on somatic growth of larger urchins (SC2 and SC3) but smaller urchins (SC1) grew significantly larger with regular feeding. However, the FCR was significantly lower in the urchins of the 1 week fed/starve treatment in SC1 and SC2 and the 50% reduction in labour costs and reduction of the amount of feed required offered by this feed regime are likely to be optimal for grow-out of juvenile urchins despite the reduced absolute growth. In the case of larger sea urchins (SC3) there was no effect on gonadal growth from the various feeding regimes indicating that intermittent feed periods of up to 4 weeks will not adversely affect gonad enhancement operations but will substantially reduce feed and labour costs. These results should be carefully considered in order to optimise feed regimes for future sea urchin on-growing and gonad enhancement ventures. (C) 2012 Published by Elsevier B.V.