Feeding rate, absorption efficiencies, growth, and enhancement of gonad production in the New Zealand sea urchin Evechinus chloroticus Valenciennes (Echinoidea: Echinometridae) fed prepared and natural diets

Small, (30-40-mm diameter) medium, (50-60-mm diameter) and large (70-80-mm diameter) Evechinus chloroticus Valenciennes collected from Doubtful Sound on the west coast of the South Island of New Zealand were held in individual containers with running seawater and fed prepared and natural diets during the austral autumn, winter, and spring. At the beginning and end of each experimental period feeding rates, absorption efficiencies, growth, and gonad and gut indices were determined. Feeding rates differed significantly between diets, urchins eating more of extruded pellets than agar-bound prepared feed or natural algal food. Feeding rate showed a clear seasonal trend directly correlated with water temperature. Absorption was quite variable but did not differ significantly between diets or with urchin size. Absorption was significantly lower in December than in other months. Gonad indices were higher in urchins fed prepared feeds than algae; however, there were seasonal differences in which of four different prepared feeds produced the largest gonads. Small urchins developed gonads when fed in the laboratory, although this size class does not develop gonads in the wild. This suggests sexual maturity may depend upon nutritional state as well as size. Prepared feeds tended to produce white- or cream-colored gonads unsuitable for sale; whereas, urchins fed algae generally formed yellow/orange gonads. Gut indices were similar in the three size classes of urchins and were generally higher in urchins fed prepared feeds. Small urchins grew proportionally more than medium or large sizes. Growth was faster on algae than prepared feeds. Although prepared feeds can enhance gonad production in Evechinus chloroticus the composition will need to be appropriate to achieve acceptable yellow/orange gonad color and better somatic growth.