The effect of the addition of algae feeding stimulants to artificial diets for the sea urchin Tripneustes gratilla

A key concern when developing artificial aquaculture diets is their palatability. This study investigated whether the palatability of artificial diets could be improved by incorporating a small quantity of highly preferred natural foods as feeding stimulants. The preference of Tripneustes gratilla for marine plants with which it co-occurs naturally in New South Wales, Australia, was assessed in a laboratory choice feeding experiment. T. gratilla displayed significant preference for the brown alga Ecklonia radiata over five other algae and one seagrass when they were offered simultaneously. Total protein or energy in the plants was not found to account for this preference. However, T. gratilla showed no preference among E. radiata, Sargassum linearifolium and Ulva lactuca when they were dried. Three artificial diets were made by incorporating one of each of these dried seaweeds at 5% dry weight. Although not statistically significant, T. gratilla ate more than twice as much the artificial diet containing S. linearifolium compared to the control diet containing no algae in a choice feeding experiment. In a no-choice feeding experiment, T. gratilla consumed significantly more of the Ecklonia and the Sargassum diets than the control diet despite each of the diets containing approximately the same protein and energy levels. T. gratilla consumed 49 and 43% more protein, and 37 and 44% more energy, respectively, when fed with the Ecklonia and the Sargassum diets compared to the control diet. Juvenile T. gratilla grew significantly faster on a wet weight basis on the Sargassum diet than the control diet at an average increase of 2.4% per day. These results indicate that the small amounts of palatable seaweed added to the artificial diets act as feeding stimulants, increasing the acceptability of artificial sea urchin diets, boosting the protein and energy consumption, and significantly increasing the growth of T. gratilla. Moreover, the fast growth of T. gratilla achieved in this study also indicates that this species would be a good candidate for commercial aquaculture.