Determination of dietary protein, carbohydrate, and lipid requirements for the sea urchin Lytechinus variegatus fed semi-purified feeds

Understanding the effects of dietary protein, carbohydrate, and lipid in Lytechinus variegatus would contribute to the development of commercial feeds for sea urchin aquaculture. Adult sea urchins were fed formulated feeds with different protein levels, protein: carbohydrate levels and lipid sources and levels to observe effects on sea urchin growth and quality. Sea urchins fed the 20% protein feed had moderate consumption, high survival, weight gain, production efficiency and protein efficiency suggesting this feed was utilized most efficiently. The protein and carbohydrate composition of the gonad varied directly with the level of these macronutrients consumed.; Image analysis indicated that the volume of nutritive phagocytes varied indirectly with dietary protein levels and the volume of the germinal epithelium and gamete numbers varied directly with dietary protein levels in the gonad. Data indicate macronutrient storage and gametogenic development are manipulated by diet. The effects of dietary protein were further evaluated with an improved feed containing protein: carbohydrate levels that bracketed the 20% protein feed. Improvements were made in feed formulation, feed physical form, experimental systems, and experimental methods. Sea urchins fed the 31:33% protein: carbohydrate feed had lower feed and energy consumption yet higher weight gain, production, production efficiency, gonad production, and gonad production efficiency.; Similar protein efficiency ratios among the feed treatments suggest protein sparing. Increases in supplemented menhaden oil levels had no effect on growth but reduced production efficiency above and below the 1% level, suggesting that a source of marine-derived fatty acids are necessary for optimal production efficiency. Increases in supplemented soy oil levels had negative effects on growth, production and production efficiency. The digestibility of dry matter, crude protein, and carbohydrate were reduced when menhaden or soy oil was supplemented at the 4% level suggesting that dietary lipid levels affect the digestibility of macronutrients. These data indicate that (1) protein is an important component of sea urchin feeds, (2) dietary protein and carbohydrate directly affect the biochemical and cellular composition of the gonad, (3) the protein:energy ratio may be important for optimizing sea urchin growth, and (4) the source and level of neutral lipid affects sea urchin growth.