Feasibility of Using Biofuel By-Products as a Sustainable Nutritional Resource for Aquaculture Production of Litopenaeus vannamei

Many different algal species can provide an acceptable protein ingredient, with good digestibility, for shrimp feeds. Compared to fish meal, similar protein, carbohydrate, and lipid levels can be found in select algal species. Traditional shrimp diets in aquaculture rely on fish meal and fish oil from pelagic fish fisheries. A reduction or elimination of these ingredients would reduce the dependency of shrimp aquaculture on offshore fisheries and increase economic competiveness. Biofuel production produces algal by-products of potential use to aquaculturists that might reduce or eliminate the need for fisheries products in shrimp feed. Established uses for by-products from biofuel production include fertilizer for crops, fodder for swine and poultry, and production of methane and alcohol fuels. However, using biofuel production by-products as a protein and carbohydrate source for the Pacific white shrimp, Litopenaeus vannamei, has not been investigated. Therefore, a series of feeding experiments were conducted to evaluate if the algae used to produce biofuel could be a suitable main protein source in formulated diets for L. vannamei. The feasibility of substituting biofuel algae by-product for fish meal in the juvenile L. vannamei (0.0306 ± 0.0011 g) diet was evaluated, and an adequate substitution ratio was determined. Eighteen experimental diets were evaluated using 60, 80, and 100% fish meal substitution levels. Chaetoceros calcitrans, Nannochloropsis salina, and Pavlova sp. were chosen as the algae sources as they have potentially high use in biodiesel production due to their high lipid content and each has been included in established larval shrimp aquaculture operations. Each diet varied the level of fish meal substitution (60, 80, or 100%) and either contained dried algal biomass or, alternatively, dried algal biomass with reduced lipid content to simulate algal biomass post-biodiesel production. The diets were compared, relative to their effect on weight gain in juvenile L. vannamei, to each other and to a commercially available diet (CONTROL) and a diet formulated using the ingredients used in all of the experimental diet formulations but without algal biomass (BASAL). The shrimp were held individually in 355-ml Styrofoam cups filled with 200-ml seawater with a salinity of 32 parts per thousand (ppt) salinity under a 12:12 light:dark photoperiod. Water exchange was 90% per day for six days and 100% on the seventh day when weights were taken. Each of the twenty diets was presented daily to seven replicate cups, each cup containing a single shrimp, for six weeks. Food was presented once per day to satiation, which was determined by the shrimp refusing additional feed. Each animal was weighed weekly. After six weeks, the shrimp were harvested and final weights were taken. The analysis of differences between strains, levels, and lipids indicated there was a significant difference between all of the algal-based diets and the control. Overall, significantly better growth rates were observed in the diets with less fish protein replacement. The 60% fish meal replaced diets outperformed the diets that had 80 or 100% fish meal replacement. There were no significant differences in nutritional value among the algal species. Survival rates, from an aquaculture perspective, were acceptable for all treatments (\u3e71%). Results from these studies demonstrated that formulated diets using algal biomass from biodiesel production can be the primary protein source for L. vannamei postlarvae