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The effects of artificial diet on gonad size, egg size, egg quality, and larval vitality in green sea urchins, Strongylocentrotus droebachiensis of aquaculture significance Westman, M. Marja de Jong


Effects of long-term dietary conditioning on gonadal growth, lipid, and moisture content, and on egg size, egg-energy content, larval morphometry, and larval development of the green sea urchin Strongylocentrotus droebachiensis were studied in the laboratory. One algal and seven artificial diets were tested over a nine-month period, coinciding with the urchin’ s annual reproductive cycle. Formulated diets differed in protein level and in the presence or absence of different supplements, such as algal storage carbohydrates (mannitol and algin), cholesterol, and B-carotene. Diets were: 1)10% protein (LO-PRO), 2)10% protein+ mannitol (LO-PRO+M), 3)10% protein+algin (LO-PRO+A), 4) 20% protein (HI-PRO), 5) 20% protein+cholesterol (HI-PRO+C), 6) 20% protein+B-carotene (HI-PRO+B), 7) 20% protein+B-carotene+cholesterol (HI-PRO+C/B), and 8) dried seaweed Nereocystis luetkeana (KELP). Urchins reared on the low-protein diet formulations had significantly smaller gonad indices than urchins conditioned on the highprotein and algal diets. Gonadal lipid and moisture contents varied significantly over time but not among dietary treatments. Significant differences in egg sizes were observed. HI-PRO produced the smallest eggs and HI-PRO+C the largest, while other diet groups produced intermediate-sized eggs. Egg organic-carbon levels also differed significantly with the largest amounts being present in HI-PRO+C/B, and the lowest in LO-PRO and HI-PRO. Larvae cultured from eggs of selected diet groups (LO-PRO, HI-PRO, HI PRO+B, HI-PRO+C/B, and KELP) showed significant differences in morphometry and in rates of development. HI-PRO+B and HI-PRO+C/B were the first to reach the feeding pluteal stage at 3 days and the 2-arm pluteus at 5-6 days. The feeding pluteal stage was attained by LO-PRO and HI-PRO at 4 days and the 2-armed larvae at 7-8 days. Larval development times for LO-PRO, HI-PRO, and HI-PRO+C/B were comparable by the 4-arm stage and remained so throughout development. HI-PRO+B larvae consistently had the shortest development times, reaching the fully-formed 8-arm larval stage 3 days earlier than larvae from other diet groups. HI-PRO+B larvae also had the highest rate of metamorphosis success. They showed significantly higher diary band/body-length ratios throughout all developmental stages, indicating greater larval feeding effectiveness and suggesting that this was the key to their overall success. All larvae arising from adults fed the artificial diets were competent; however, larvae from adults fed KELP showed severe abnormalities and subsequent early mortality. With regard to an aquaculture program, I conclude that HI-PRO+B is the best of the diets tested, in that it supported high gonathi growth for the roe market, and produced healthy broodstock with resultant vigorous larvae.

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