Tilapia is one of the most widely cultured species of fish in the world for human consumption, as a forage for sport fish, and for biological control of nuisance vegetation. To keep pace with their rapid production, tilapia aquaculture should rely on sustainable practices. Since feed constitutes a major operating expense, cost effective sustainable ingredients should be utilized in their diets. Black soldier flies, Hermetia illucens , are found worldwide and can be economically and sustainably produced using waste products such as food remains and manure. Black soldier fly meal has been successfully incorporated into aquaculture diets at varying levels. Since the protein, fat, and ash content of the black soldier flies has been shown to be affected by the feed source they consume, care needs to be undertaken with their diet. One potential source of black soldier fly feed may be obtained from harvested algal turf scrubber biomass. Algal turf scrubbers are a simple system which pulses nutrient rich water over a sloped flow-way to produce an algal biomass. The biomass is harvested periodically to maintain system performance. Harvested algal turf biomass has previously been used for sea urchin feed as well as a supplement in potting soil. This study was conducted to determine the suitability of algal turf scrubber biomass fed black soldier flies as a dietary ingredient in practical tilapia diets.
Algae turf scrubber biomass was harvested weekly from a 9.14-meter algal turf scrubber placed at the outflow of the Statesboro wastewater treatment facility . The turf scrubber biomass was utilized as the sole feed source for black soldier fly larvae which were reared based on established protocols. Black soldier fly larvae were processed into a meal which was incorporated into the soybean meal dominant tilapia diets. Four diets were formulated to include a control diet (6% fishmeal), 50 and 100% fishmeal replacement with our black soldier fly meal, and a 100% fishmeal replacement with a commercial black soldier fly meal. These were tested along with a commercial tilapia diet. Juvenile blue tilapia were stocked into thirty 60.6-liter polyethylene tanks connected by a recirculating water filtration system to provide six replicates per treatment with six tilapia per tank. Tilapia were fed twice daily for the duration of the 6-week feeding trial. At the end of the growth tria l an in-vivo digestibility trial was done to assess the digestibility of our and the commercial black soldier fly meal.
After 6 weeks, blue tilapia fed the 5 different diets showed no differences with respect to growth, survival, hepatosomatic index, visceral index, intraperitoneal fat, or muscle mass. There was also no significant difference in protein digestibility between our and the commercial black soldier fly meal. This study demonstrated a sustainable solution to utilize algal turf biomass in tilapia diets.