WEIGHT GAIN OF THE SHRIMP Litopenaeus vannamei IS ENHANCED BY CONSUMPTION OF SEA URCHIN EGESTA

Typically, solid waste produced in a recirculating system is systematically removed to ensure health of the cultured species. Removal of these solids represents a loss of nutrients and energy that remain unassimilated. In culture, urchins produce fecal pellets that are membrane bound and contain residual nutrients and large quantities of microbiota; these egesta have the potential to be highly nutritious. We are currently investigating the feasibility of sea urchin/shrimp polyculture to increase the utilization of feed and feed waste and optimize food conversion ratios. Initial studies indicated that shrimp are able to survive and grow on urchin egesta alone with no treatment-dependent mortality. The goal of this study was to determine if a supplementation of urchin egesta could improve growth and feed efficiency of shrimp fed a commercial shrimp diet.

Shrimp were stocked in groups of four (average individual weight: 0.69 g) into 80L tanks in an interconnected recirculating aquaculture system. Each tank contained a floating mesh basket with a false floor intended to house sea urchins separately from the shrimp while allowing any egesta from the urchins to fall below for consumption by the shrimp. Tanks were assigned randomly into one of seven treatments that varied in level of a 40% protein commercial shrimp feed provided and the presence or absence of sea urchins. When present, urchins were fed a formulated diet at 3% body weight daily. Shrimp were fed to a 100% level based on an estimated growth of 0.8 g per week and a 1.8 FCR. Treatments included: 20% shrimp feed ration only (20% SF); 60% shrimp feed ration only (60% SF); 100% shrimp feed ration only (100% SF); 0% shrimp feed ration with urchins (UE ONLY); 20% shrimp feed ration with urchins (20% SF+UE); 60% shrimp feed ration with urchins (60% SF+UE); and 100% shrimp feed ration with urchins (100% SF+UE). The trial was terminated after 8 weeks.

Shrimp held in culture with urchins showed increased weight gain when compared to those receiving shrimp feed only. Urchin egesta fed alone performed well compared to a full ration of shrimp feed alone, indicating either direct or indirect nutritional benefit is provided by the urchin egesta.