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Notes: Pilot-scale trials were conducted to evaluate growout performance of hatchery-reared summer flounder fingerlings in a state-of-the-art recirculating aquaculture system (RAS). The outdoor RAS consisted of four 4.57-m dia × 0.69-m deep (vol. =11.3 m3) covered, insulated tanks and associated water treatment components. Fingerlings (85.1 g mean initial weight) supplied by a commercial hatchery were stocked into two tanks at a density of 1,014 fish/tank (7.63 kg/m3). Fish were fed an extruded dry floating diet consisting of 50% protein and 12% lipid. The temperature was maintained between 20 C and 23 C and the salinity was 34 ppt. Under these conditions, growth, growth variation (CVwt), feed utilization, and survival of fish fed to 100% and 82% of a satiation rate were compared.Due to clear changes in growth patterns during the study, data was analyzed in three phases. During phase 1 (d 1–d 196), fish showed rapid growth, reaching a mean weight of 288 g ± 105 and 316 g ± 102, with a CVwt of 0.36 and 0.32 and FCR's of 1.38 and 1.36 in the subsatiation and satiation groups, respectively. During phase 2 (d 196–d 454), fish displayed slower growth reaching mean weights of 392 g ± 144 and 436 g ± 121, with a CVwt of 0.37 and 0.28, and increasing FCR's of 3.45 and 3.12 in the subsatiation and satiation groups, respectively. During phase 3 (d 454–d 614), fish showed little growth reaching mean weights of 399 g ± 153 and 440 g ± 129, with a CVwt of 0.38 and 0.29 in the subsatiation and satiation groups, respectively. Over the entire growout period (d 1–d 614), feed conversion ratios were 2.39 and 2.37 and survival was 75% and 81 % in the subsatiation and satiation treatments, respectively. The maximum biomass density reached during the study was 32.3 kg/m3.The satiation feed rate was superior to the 82% satiation rate, since it maximized growth rates, with no effect on FCR. The higher CVwt in the subsatiation group suggests increased competition for a restricted ration led to a slower growth with more growth variation. The decrease in growth in phases 2 and 3 was probably related to a high percentage of slower growing male fish in the population and the onset of sexual maturity.This study demonstrated that under commercial scale conditions, summer flounder can be successfully grown to a marketable size in a recirculating aquaculture system. Based on these results, it is recommended that a farmer feed at a satiation rate to minimize growout time. More research is needed to maintain high growth rates through marketable sizes through all-female production and/or inhibition of sexual maturity.

Notes: Aquaculture production in recirculating systems has been the focus of research and development efforts for decades. Although considerable resources have been expended on these systems in the private sector, there is a scarcity of data on the economic or engineering performance of commercial scale recirculating production systems. This paper presents the results of a computer simulation of tilapia production in a small recirculating production system. Much of the performance data has been developed at a demonstration facility at North Carolina State University. Given the assumptions of the base case simulation, the cost of producing a kilogram of tilapia in the recirculating system described is estimated to be $2.79 ($1.27/lb). The results of a model sensitivity analysis indicate that while improvements in the performance efficiency of system components did not greatly affect fish production costs, reductions in feed costs and improvements in the feed conversion ratio caused the greatest reduction of production cost of all of the operational variables investigated. The analysis further indicates that the greatest gains to be realized in improving profitability are those associated with increasing the productive capacity or decreasing the investment cost of a recirculating fish production system.

Notes: A study to determine the effects of four stocking densities on growth and feed utilization of wild-caught black sea bass Centropristis striata was conducted in a pilot-scale recirculating tank system. The outdoor system consisted of 12 insulated fiberglass tanks (dia. = 1.85 m; vol. = 2.17 m3) supported by biological filters, UV sterilizers, and heat pumps. Subadults (N= 525; ×± SD = 249 ± 16.8 g) were stocked at densities of 4.6 fish/m3 (1.18 kg/m3), 16 fish/ m3 (3.91 kg/m3), 25.3 fish/m3 (6.83 kg/m3), and 36 fish/m3 (7.95 kg1m3), with three replicate tanks per treatment. Fish were grown under 35 ppt salinity, 21-25 C, and under ambient photoperiod conditions. A commercial flounder diet containing 50% protein and 12% lipid was hand-fed twice daily to satiation for 201 d.Mean (range) total ammonia-nitrogen, 0.61 (0-2.1) mg/L, nitrite-nitrogen, 0.77 (0.04-3.6) mg/L, and nitrate-nitrogen 40.1 (0-306) mg/L were significantly higher (P 〈 0.0001) in the 25.3 and 36 fish/m3 treatments than in the 4.6 and 16 fish/m3 treatments [0.19 (0.05-0.5), 0.1 (0.24-0.63), and 11.9 (1.3-82.2) mg/L, respectively]. However, there were no significant differences (P 〉 0.05) in growth (RGR = 196.8-243.1%; DWG = 2.55-2.83 g/d; and SGR = 0.55-0.61%/d), coefficient of variation of body weight (CwtV., = 0.24-0.25), condition factor (K = 2.2-2.4), feed consumption (FC = 1.45-1.65%/d), and feed conversion ratio (FCR = 1.45-1.52) among stocking densities. Final biomass densities on day 201 reached 3.48, 12.0, 21.1, and 27.2 kg/m3 at stocking densities of 4.6, 16, 25.3, and 36 fish/m3, respectively. Survival (83.8-99.1%) did not differ among treatments. Apparent net protein retention (ANPR) was significantly higher (P 〈 0.005) for fish stocked at the lower densities of 4.6 and 16 fish/m3 (22.5-23.7%) than for those stocked at 25.3 and 36 fish/m3 (21-20.1%). There were no significant differences (P 〉 0.05) in apparent net energy retention (ANER = 55.9-59.1 %) among stocking densities. Final whole body protein (15.3-16.3%) and lipid (23.1-26.4%) levels did not differ significantly (P 〉 0.05) among treatments.The results demonstrated that growth, survival, and feed utilization were not impaired under stocking densities ranging from 4.6-36 fish/m3 (3.48-27.2 kg/m3), despite a slight reduction in water quality at the higher densities. In addition, growth variation and final whole body protein and lipid levels were not influenced by these densities. The results suggest that black sea bass are tolerant of crowding and moderate variations in water quality during intensive culture in recirculating tank systems and that higher stocking densities are possible.