Evaluation of Stocking Density during Second-Year Growth of Largemouth Bass, Micropterus salmoides, Raised Indoors in a Recirculating Aquaculture System

Largemouth bass (LMB), Micropterus salmoides, are a highly desirable food fish especially among Asian populations in large cities throughout North America. The primary production method for food-size LMB (>500 g) has been outdoor ponds that require two growing seasons (18 mo). Indoor, controlled-environment production using recirculating aquaculture system (RAS) technologies could potentially reduce the growout period by maintaining ideal temperatures year-round. Researchers conducted a 26-wk study to evaluate optimal stocking densities for growout of second-year LMB to food-fish size in an indoor RAS. LMB fingerlings (112.0 +/- 38.0 g) were randomly stocked into nine 900-L tanks to achieve densities of 30, 60, or 120 fish/m(3) with three replicate tanks per density. The RAS consisted of a 3000-L sump, 1/4 hp pump, bead filter for solids removal, mixed-moving-bed biofilter for nitrification, and a 400-watt ultraviolet light for sterilization. Fish were fed a commercially available floating diet (45% protein and 16% lipid) once daily to apparent satiation. At harvest, all fish were counted, individually weighed, and measured. Total biomass densities significantly increased (P <= 0.05) with stocking rate achieving 6.2, 13.2, and 22.9 kg/m(3) for fish stocked at 20, 60, and 120 fish/m(3), respectively. The stocking densities evaluated had no significant impact (P > 0.05) on survival, average harvest weight, or feed conversion ratio which averaged 92.9 +/- 5.8%, 294.5 +/- 21.1 g, and 1.8 +/- 0.3, respectively. After approximately 6 mo of culture, LMB did not attain target weights of >500 g. Observed competition among fish likely resulted in large size variability and overall poor growth compared to second-year growth in ponds. Additional research is needed to better assess the suitability of LMB for culture in RAS.