Library

Notes: The effects of four practical diets on growth, feed utilization, and body composition of wild-caught juvenile and subadult black sea bass Centropristis striata (316 ± 113 g =±± SD) were compared for 221 d in a recirculating tank system consisting of 12 2,660-L tanks. Salinity averaged 33.5 ppt and temperature averaged 20.9 C but vaned from 12 to 27.1 C. Diets differed in crude protein (CP) and crude lipid (CL) as follows: 1) low CP (44.0%), low CL (11.4%) trout diet; 2) low CP (44.8%), high CL (15.0%) trout diet; 3) midlevel CP (47.9%), midlevel CL (12.8%) Bounder diet; and 4) high CP (53.9%), high CL (15.1%) marine finfish diet. Energy: protein ratios (E: P) were 44.6, 45.3, 41.8, and 39.1 W/g.Survival to 221 d on all diets was 100%. Significant (P 〈 0.05) differences in growth rates were observed among diets. Final weights were higher for midlevel and high CP diets 3 and 4 (1,051 and 1,013 g) than for low CP diet 1 (873 g). Relative growth rate (RGR, % total increase in weight), specific growth rate (SGR, % increase in body weight/d), and daily weight gain (DWG, g/d) were higher for higher CP diets 3 and 4 (RGR = 223 and 221; SGR = 0.53; DWG = 3.28 and 3.16), than for low CP diet 1 (RGR = 181; SGR = 0.47; DWG = 2.54). There were no significant differences between initial and final whole body protein and fiber content among diets. Lipid and gross energy levels significantly increased (P 〈 0.0001) in all treatments while moisture levels significantly decreased (P 〈 0.001).Although these differences were not significant, feed conversion ratio (FCR = dry weight fed/wet weight gain) was lower for fish given midlevel CP diet 3 (1.49) and high CP diet 4 (1.52) than for those fed low CP diets 1 and 2 (1.60 and 1.62). Protein efficiency ratios (PER = weight gain/weight protein fed) (1.43 to 1.24), apparent net protein retention (ANPR = weight protein gain/weight protein fed) (20 to 25%), and apparent net energy retention (ANER = energy gain/energy fed) (53.3 to 56.8%) were not significantly different among treatments. The midlevel CP (50%), midlevel CL (12%) diet maximized growth rates and was also significantly less expensive per kg fish weight produced ($1.40) than the high CP diet ($1.94) which produced the second highest growth rates. These results demonstrated that wild-caught black sea bass can be successfully reared in recirculating tanks from juvenile to marketable sizes with high survival and with good feed conversion and growth on commercially prepared diets with a wide range of protein and lipid levels.

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: Hormone-induced spawning of southern flounder Paralichthys lethostigma has produced substantial numbers of viable eggs, but wide variations in fertilization and hatch rates have been reported. Recently, sustained natural spawning of southern flounder broodstock, without hormone induction, has been achieved in our laboratory. Adults (average weight = 1.12 kg; N= 25), including 6 captured as juveniles in 1993 and 19 captured as adults during September 1998, were stocked in two 4.8-m3 controlled-environment tanks in October 1998 and held under natural photothermal conditions until January 1999, when an artificial winter photo-period of 10 L:14 D was initiated and then maintained through April 1999. Sex ratio was approximately 13 females:8 males:7 unknown. Natural spawning was observed in early December 1998 and increased in frequency to a peak in March 1999, before declining in late April. Water temperature ranged from 13.9 to 24.5 C during the spawning period. Natural spawnings over 142 d produced a total of 18.3 × 106 eggs, with a mean fertilization rate of 28.0% (range = 0–100%), yielding 4.94 × 106 fertilized eggs. The mean percentage of eggs that remained buoyant in full-strength seawater (34 ppt) was 41.3% (0–98%), while hatching rate of buoyant eggs was 37.3% (0–99%) and survival of yolksac larvae to the first-feeding stage was 30.2% (0–100%). Gonadal biopsies in late April identified six females from both tanks as probable spawners. A preliminary comparison suggests that natural spawning produced much larger numbers of viable eggs per female, with higher egg quality (i.e., fertilization and hatching success) than hormone-induced spawning. In contrast to natural spawning, hormone-induced strip-spawning enabled timing of spawnings to be more precisely controlled. These results suggest that a combination of both natural and hormone-induced spawning of photothermally conditioned fish will help produce the large numbers of eggs required to support commercial production.

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.