MACRONUTRIENT ALLOCATION VARIES WITH DIETARY PROTEIN AND CARBOHYDRATE LEVELS IN THE SEA URCHIN Lytechinus variegatus

The increasing demand for sea urchin roe in the food industry and the decrease in wild sea urchin stocks has increased interest in the development of large-scale commercial sea urchin aquaculture. Many studies have examined nutritional requirements to promote growth and production among sea urchins.  However, dietary macronutrients may also influence nutrient allocation and subsequent biochemical composition of gonad tissue, which could directly affect the quality of sea urchin roe.

In a 10-week growth and production trial, juvenile Lytechinus variegates (3.95±0.54 g wet weight) were fed 6 semi-purified formulated diets with three different protein (11, 27 and 43%) and two carbohydrate levels (12 and 18%). All other nutrient levels were held constant. Each sea urchin (n = 16 per treatment) completely consumed a sub-satiation ration of 2.0% of the average body weight per day. Individuals were weighed and dissected at the end of 10 weeks to evaluate the gonad.

Gonad dry matter production was not correlated to dietary carbohydrate levels (Fig.1). However, there was a direct correlation between dietary protein levels and gonad dry matter production. Individuals fed the 11% protein diet had significantly less gonad dry matter production than individuals fed the 27 or 43% protein diets, indicating that protein level in the diets is positively correlated with the size of the gonad.

Under the conditions of this study, significant changes in crude protein, carbohydrate and lipid content in the gonads were associated with dietary carbohydrate and protein levels (Fig.2). High protein diets were correlated with high crude protein content of gonads (up to 62% dry weight). High carbohydrate diets were correlated with increased carbohydrate content of gonads (up to 26% dry weight). Gonad lipid content ranged from 20- 38% dry weight, with the highest lipid levels found among urchins fed the diet containing low levels of protein and carbohydrate (11P:12C). These data indicate that nutrient allocation varies significantly with dietary macronutrients. We hypothesize that gonad composition will affect roe flavor and commercial appeal.