Production and economic optimization of dietary protein and carbohydrate in the culture of Juvenile Sea Urchin Lytechinus variegatus

• Juvenile Lytechinus variegatus were fed 10 formulated diets with different protein and carbohydrate levels.
• Growth and production were generally predicted to increase with increasing level of dietary protein up to ca. 30%.
• The energetic cost of dry matter production was optimal at protein levels less than those required for maximal weight gain and gonad production.
• For both 18 and 12% levels of dietary carbohydrate, cost per gram of wet weight gain is predicted to be maximized at low dietary protein levels.

Juvenile Lytechinus variegatus (ca. 3.95 ± 0.54 g) were fed one of 10 formulated diets with different protein (ranging from 11 to 43%) and carbohydrate (12 or 18%; brackets determined from previous studies) levels. Urchins (n = 16 per treatment) were fed a daily sub-satiation ration equivalent to 2.0% of average body weight for 10 weeks. Our objective was (1) to create predictive models of growth, production and efficiency outcomes and (2) to generate economic analysis models in relation to these dietary outcomes for juvenile L. variegatus held in culture. At dietary protein levels below ca. 30%, models for most growth and production outcomes predicted increased rates of growth and production among urchins fed diets containing 18% dietary carbohydrate levels as compared to urchins fed diets containing 12% dietary carbohydrate. For most outcomes, growth and production was predicted to increase with increasing level of dietary protein up to ca. 30%, after which, no further increase in growth and production were predicted. Likewise, dry matter production efficiency was predicted to increase with increasing protein level up to ca. 30%, with urchins fed diets with 18% carbohydrate exhibiting greater efficiency than those fed diets with 12% carbohydrate. The energetic cost of dry matter production was optimal at protein levels less than those required for maximal weight gain and gonad production, suggesting an increased energetic cost (decreased energy efficiency) is required to increase gonad production relative to somatic growth. Economic analysis models predict when cost of feed ingredients are low, the lowest cost per gram of wet weight gain will occur at 18% dietary carbohydrate and ca. 25–30% dietary protein. In contrast, lowest cost per gram of wet weight gain will occur at 12% dietary carbohydrate and ca. 35–40% dietary protein when feed ingredient costs are high or average. For both 18 and 12% levels of dietary carbohydrate, cost per gram of wet weight gain is predicted to be maximized at low dietary protein levels, regardless of feed ingredient costs. These models will compare dietary requirements and growth outcomes in relation to economic costs and provide insight for future commercialization of sea urchin aquaculture.Statement of relevanceThis paper uses general linear modeling to predict growth, production and efficiency in cultured L. variegatus within an optimal range of dietary carbohydrate levels (12 or18%) at different levels of dietary protein. Data were used to generate economic analysis models for high, medium and low feed ingredient prices. We believe that these data are the first to provide any information regarding the economic viability of sea urchin aquaculture. Further economic analysis will be required to estimate costs of labor and culture systems. However, these data may prove to be useful and informative in predicting feed costs for urchins held in culture.