The balancing act: Protein, lipid and seaweed dietary levels to maximize gonad quantity in a wild-caught sea urchin

Sea urchin gonads (roe) are a prized global sea food commodity, with growing demand driving the need for urchin roe enhancement aquaculture. Effective roe enhancement of urchins using formulated feeds require species-specific optimization and an understanding of the interactions between key dietary components (e.g. protein, lipid, carbohydrate, energy and/or algal supplements). Here, we tested 18 formulated feeds on the sea urchin Heliocidaris erythrogramma, collected from barrens. The 18 iso-energetic (~20 MJ/kg) feed combinations contained one of three protein levels (250, 375 or 500 g/kg), three lipid levels (73, 101 or 131 g/kg) combined with a single (45 g/kg Sargassum spp.) or multiple (45 g/kg Sargassum spp., 25 g/kg Solieria robusta, 25 g/kg Ulva lactuca) dried algal supplement. From two consecutive 12-week enhancement trials, the most optimal feed type contained 375 g/kg protein, 73 g/kg lipid and a 45 g/kg algal supplement (Sargassum spp.) and produced gonad indices of 18.5 ± 0.4% (Trial 1) and 21.7 ± 1.2% (Trial 2). Across feed types, there was no significant difference in the proportion of marketable quality (A and B grade) roe produced (56%–85% Trial 1, 65%–85% Trial 2). We conclude that roe enhancement of H. erythrogramma collected from barrens is highly feasible.