Maximum yield approximation and size distribution patterns of stocker size largemouth bass,Micropterus salmoides reared in a semi‐closed indoor system

The main objectives of this study were to approximate the maximum yield and evaluate size dispersion of stocker size largemouth bass, Micropterus salmoides reared in a semi‐closed recirculating system for 60 days. Fingerlings with an average body weight of 36.7 g were utilized for the study. An experimental system consisting of 18 square plastic tanks (165 L) equipped with a radial flow settler, a sump, a moving bed filter, a centrifugal pump, a rapid sand filter, a down‐flow oxygen saturator and a UV sterilizer was utilized for the trial. The system was operated semi‐closed, accounting for a daily exchange rate of 30–50% of total system water volume. Experimental stocking densities were 4.5, 9.1, 18.8, 36.5, 54.6 and 73 kg m^?3 with three replicates per treatment. At the end of the experimental trial, largemouth bass showed acceptable feed conversion (1.00–1.48), specific growth rate (1.16–1.45% day^?1) and survival rate (81.8–96.6%) in all treatments, displaying the highest performance at an initial stocking density range of 18–36 kg m^?3. Based on a piecewise regression model with breakpoint analysis, maximum yield of largemouth bass fingerlings should not exceed 70 kg m^?3. As stocking density increased, relatively more underweight fingerlings were produced with a higher uniformity of fatness.     

Effects of predation by largemouth bass in fish production ponds stocked with Tilapia nilotica

Triplicate ponds (0.07 ha) were stocked with either 0, 29, 86, or 143 largemouth bass fingerlings and 9500 Tilapia nilotica fingerlings (90% males) per hectare. Fish were fed a 32% protein ration for 6 months and then harvested. Average weight of largemouth bass declined as their stocking density increased. Average weight and total biomass of originally stocked tilapia increased with increasing predator stocking density. Total yields of tilapia were not different and averaged 4203, 4355, 4583 and 4230 kg/ha, of which recruits accounted for 28, 29, 26 and 8% for the above respective predator densities. Stocking 143 largemouth bass per hectare was an effective means of decreasing recruitment and increasing yields of larger sized male tilapia.     

Growth and production of hatchery-reared juvenile spotted babylon Babylonia areolata Link 1807 cultured to marketable size in intensive flowthrough and semi-closed recirculating water systems

Hatchery‐reared juvenile spotted babylon Babylonia areolata (mean initial shell length 12.8 mm) were cultured intensively to marketable size in three 3.0 × 2.5 × 0.7 m indoor canvas rectangular tanks. The duplicate treatments of flowthrough and semi‐closed recirculating sea‐water systems were compared at an initial stocking density of 300 individuals m^?2 (2250 juveniles per tank). The animals were fed ad libitum with fresh carangid fish Selaroides leptolepis once daily. During 240 culture days, average growth rates in shell length and body weight were 3.86 mm month^?1 and 1.47 g month^?1 for the flowthrough system and 3.21 mm month^?1 and 1.10 g month^?1 for those in the semi‐closed recirculating system. Survival in the flowthrough system (95.77%) was significantly higher than that in the semi‐closed recirculating system (79.28%). Feed conversion ratios were 1.68 and 1.96 for flowthrough and semi‐closed recirculating systems respectively.     

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/m³ with three replicate tanks per density. The RAS consisted of a 3000‐L sump, ¼ 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/m³ for fish stocked at 20, 60, and 120 fish/m³, 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.     

Stocking Density Effects on Production Characteristics and Body Composition of Market Size Cobia,Rachycentron canadum,Reared in Recirculating Aquaculture Systems

Culture density in excess of a critical threshold can result in a negative relationship between stocking density and fish production. This study was conducted to evaluate production characteristics of juvenile cobia, Rachycentron canadum, reared to market size in production‐scale recirculating aquaculture systems (RAS) at three different densities. Cobia (322 ± 69 g initial weight) were reared for 119 d at densities to attain a final in‐tank biomass of 10, 20, or 30 kg/m³. The specific objective was to determine the effects of in‐tank crowding resulting from higher biomass per unit rearing volume independent of system loading rates. Survival was ≥96% among all treatments. Mean final weight ranged from 2.13 to 2.15 kg with feed conversion efficiencies of 65–66%. No significant differences were detected in growth rate, survival, feed efficiency, or body composition. This study demonstrates that cobia can be reared to >2 kg final weight at densities ≤30 kg/m³ under suitable environmental conditions without detrimental effects on production.     

Effect of Intensification on Grow Out of the Amazon River Prawn, Macrobrachium amazonicum

The effects of intensification on growth, survival, productivity, population structure, and distribution of harvested biomass in individual size classes of Macrobrachium amazonicum in semi‐intensive culture were evaluated. Postlarvae (0.01 g) were stocked in 12 ponds at densities of 10, 20, 40, and 80/m² (three replicates per treatment) and raised for 5.5 mo. Average individual weight significantly decreased and productivity significantly increased as stocking density increased (P < 0.001), while survival was not affected (P > 0.05). Prawn mean weight at harvest ranged from 3.6 (80/m²) to 7.0 g (10/m²). Average survival ranged from 65.5% (40/m²) to 72.8% (20/m²), while productivity ranged from 508 (10/m²) to 2051 kg/ha (80/m²). Harvested biomass showed a clear bimodal distribution in individual size classes indicating the occurrence of heterogeneous growth, which may affect management and market strategies. Harvested biomass of prawns weighing more than 7 g (the best market size) increases for stocking densities up to 40/m² and stabilizes between 40 and 80/m². Growth reduction was associated with a decreasing frequency and average weight of green claw 1 and green claw 2 male morphotypes and adult females as density increased. Thus, the distribution of male morphotypes and sexually mature females are affected by density‐dependent factors. Results suggest that prawn density plays an important role on M. amazonicum grow‐out phase, as has been demonstrated for other species of the genus Macrobrachium. M. amazonicum tolerates grow‐out intensification and may be raised in both semi‐intensive and intensive systems stocked at very high densities yielding high productivity.     

Feasibility of Pond Production of Largemouth Bass,Micropterus salmoides,for a Filet Market

The effects of stocking density on food‐size largemouth bass (LMB), Micropterus salmoides, production (>0.5 kg) were evaluated in a 2‐yr study by stocking LMB fingerlings (mean weight = 57 g/fish) in 0.1‐ha earthen ponds at rates of 6175, 12,350, or 18,525 fish/ha. Gross yields increased from 3989 to 9096 kg/ha as stocking density increased. No significant differences were observed in survival rates (range of 65–74%) due to density. Maximum feed consumption occurred at water temperatures of 27–30 C. Feed conversion ratio (FCR) and mean harvest weight were significantly different (P < 0.05) among densities, with the lowest FCR and the lowest mean weight found at the highest density (18,525 fish/ha). At harvest, LMB were considered to be in good condition with relative weight (W_r) values of 123–124. Dressout yield percentages were 61–62% for whole‐dressed LMB and 34–35% for shank filets. LMB grew well and reached a size adequate for targeted shank filet sizes. However, the production costs of $7.26–$9.34/kg mean that LMB production for a filet market is unlikely to be feasible. Research to lower LMB fingerling and feed costs and improved FCR would contribute to improved economic feasibility.     

养殖密度对池塘工程化循环水养殖大口黑鲈抗氧化力、组织结构及应激基因表达的影响

为研究池塘工程化循环水养殖模式下养殖密度对大口黑鲈（应激基因表达的影响,以初始体重（4.50±0.23）g的大口黑鲈幼鱼为研究对象,设置3个养殖密度组,分别为0.2 kg/m³（SD1）、0.4 kg/m³（SD2）和0.6 kg/m³（SD3）,每个密度组设3个重复,实验周期为120 d,分别在实验的第30天、60天、90天和120天采集样本并分析。结果显示,实验结束时的最终密度分别为5.64 kg/m³（SD1）、8.79 kg/m³（SD2）和11.21 kg/m³（SD3）。养殖前90 d,肝脏超氧化物歧化酶（SOD）、过氧化氢酶（CAT）活力在各密度组间差异不显著（<0.05）;30 d和60 d时肝脏丙二醛（MDA）含量未受到养殖密度的影响（<0.05）;各密度组间肠道淀粉酶、脂肪酶活力没有显著差异（ mRNA相对表达水平在30 d和60 d没有显著差异（<0.05）,SD1组肝脏<0.05）;切片结果显示,3个密度组实验鱼肝脏和肠道结构正常,未受到严重损害,SD3组实验鱼肝脏细胞间空泡稍增多,肠道杯状细胞变小,数量减少。综上所述,在本实验条件下,养殖后期,养殖密度会对加州鲈生理状态产生影响,高密度应激会导致鱼体抗氧化以及免疫功能受到抑制,肝脏、肠道组织产生轻微损伤,0.2 kg/m³密度组大口黑鲈的生理状况最好。综合考虑,池塘工程化循环水养殖模式下大口黑鲈幼鱼的放养密度以0.2~0.4 kg/m³为宜。     

陆基圆池循环水条件下养殖密度对大口黑鲈生长及养殖效能的影响

为研究陆基圆池循环水养殖条件下大口黑鲈(Micropterus salmoides)适宜的养殖密度,设置55、65、75、85、95尾/m²等5种养殖密度(分别标记为A1、A2、A3、A4、A5组),进行了63 d的大口黑鲈养殖试验,通过测定和分析试验鱼的体质量日增长率、体长日增长率、饲料系数、体质量均匀度和单位面积产量等指标,评价不同养殖密度对大口黑鲈生长和主要养殖效能的影响。结果显示:(1)从次低密度的A2组(65尾/m²)至密度最高的A5组(95尾/m²),试验鱼的体长日增长率基本上随着养殖密度的提高而下降,最高的A2组比A3、A4和A5组分别高了31.6%、82.9%和92.3%,并且差异显著(P<0.05);(2)从A2组至A5组,试验鱼的体质量日增长率和特定生长率均随着养殖密度的提高而下降;(3)A2组的饲料系数比A1、A3、A4和A5组分别降低了16.7%、28.6%、55.4%和56.9%;(4)单位面积产量和产品均匀度均在A2组达到最高。基于生长性能及养殖效能的综合评价,陆基圆池循环水养殖条件下大口黑鲈成鱼养殖阶段较适宜的养殖密度为65尾/m²。     

Effect of Feeding Frequency, Water Temperature, and Stocking Density on the Growth of Tiger Puffer, Takifugu rubripes

Effects of daily feeding frequency, water temperature, and stocking density on the growth of tiger puffer, Takifugu rubripes, fry were examined to develop effective techniques to produce tiger puffer in a closed recirculation system. Fish of 4, 14, and 180 g in initial body weight were fed commercial pellet diets once to five times a day to apparent satiation each by hand for 8 or 12 wk at 20 C. Daily feeding frequency did not affect the growth of 14‐ and 180‐g‐size fish. However, the daily feed consumption and weight gain of the 4‐g‐size fish fed three and five times daily were significantly higher than those of fish fed once daily (P < 0.05). Fish of 4 and 50 g in initial body weight were reared with the pellet diet at 15–30 C for 8 wk. The weight gain of fish increased with increasing water temperature up to 25 C and decreased drastically at 30 C for both sizes. Similar trends were observed for feed efficiency, although 4‐g fish had highest efficiency at 20 C. Effects of stocking density on growth were examined with fish of 8, 13, and 100 g in initial body weight. Fish were reared with the pellet diet for 8 or 16 wk at 20 C. Fish were placed in floating net cages in the culture tank, and the stocking density was determined based on the total weight of fish and volume of the net cage. Fish of 8 g in body weight grew up to 35–36 g during the 8‐wk rearing period independent of the stocking density of 8, 15, and 31 kg/m³ at the end of rearing. Final biomass per cage reached 32, 60, and 115 kg/m³ for 13‐g‐size fish, and 10, 18, and 35 kg/m³ for 100‐g‐size fish, and the growth of the fish tended to decrease with increasing stocking density for both sizes.     

Growth and Feed Utilization of Captive Wild Black Sea Bass Centropristis striata at Four Different Densities in a Recirculating Tank System

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 (C_wtV., = 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.     

Cage culture of sutchi catfish, Pangasius sutchi (Fowler 1937): effects of stocking density on growth, survival, yield and farm profitability

The sutchi catfish, Pangasius sutchi (Fowler 1937) was grown at 10 stocking densities in cages suspended in a river‐fed channel during the summer of 2000. Catfish fingerlings (mean length 9.1–9.7 cm and mean weight 5.9–6.7 g) were stocked at densities of 60, 70, 80, 90, 100, 110, 120, 130, 140 and 150 fish m^?3. After 150 days, growth and yield parameters were studied and a simple economic analysis was carried out to calculate profitability. The mean gross yield ranged from 15.6±0.27 to 34.5±0.44 kg m^?3 and the net yield ranged from 15.2±0.22 to 33.5±0.36 kg m^?3 and showed significant variations (P<0.05). The mean weights of fish at harvest were inversely related to stocking density. Both gross and net yields were significantly different and were directly influenced by stocking density but the specific growth rate, survival rate and feed conversion rate were unaffected. Higher stocking density resulted in higher yield per unit of production cost and lower cost per unit of yield. The net revenue increased positively with increasing stocking density. A density of 150 fish m^?3 produced the best production and farm economics among the densities tested in this experiment.     

High dietary starch inclusion impairs growth and antioxidant status,and alters liver organization and intestinal microbiota in largemouth bass Micropterus salmoides

Five diets (D1, D2, D3, D4 and D5) containing 0, 50, 100, 150 and 200 g starch per kg diet were formulated to investigate the effects of starch level on largemouth bass, Micropterus salmoides. Fish (initial weight: 22.00 ± 0.02 g) were fed the five diets for 90 days. Results indicated that weight gain, specific growth rate and survival of fish fed higher dietary starch level (200 g/kg) were lower than those of fish fed the lower dietary starch levels (0–50 g/kg). Higher dietary starch levels (150–200 g/kg) have a negative effect on antioxidant ability (total superoxide dismutase: T‐SOD; malonyldialdehyde: MDA; total antioxidant capacity: T‐AOC; glutathione peroxidase: GSH‐Px) and liver health (cellular contents leaked, nucleus deformed, endoplasmic reticulum and golgi body disappeared) of largemouth bass. Lower dietary starch levels (0–50 g/kg) modified intestinal microbiota of largemouth bass represented by increasing the relative abundance of beneficial bacterial such as Bacilli, Lactobacillales and Bacteroidales. These results indicated that dietary starch level above 50 g/kg had a negative effect on growth performance and antioxidant status of largemouth bass. Moreover, high dietary starch levels are potentially associated with negative alterations in liver structure and function, and decrease of beneficial gut microbes.     

Effect of Density at Harvest on the Growth Performance and Profitability of Hatchery‐reared Spotted Rose Snapper,Lutjanus guttatus,Cultured in Floating Net Cages

This study evaluated the effect of the density at harvest on the performance and profitability of hatchery‐reared spotted rose snapper cultured in cages. The fish were stocked at harvest densities of 15, 20, and 22 kg/m³ in cages of 222 and 286 m³. More than 39,000 snapper fingerlings with an initial weight of 14 g were stocked. The fish were fed an extruded diet and cultured over a 360 d period. The thermal growth coefficient ranged from 0.04 to 0.05 and survival was 95% for all treatments, with the highest final weight (436.8 g) observed for fish reared at a density of 20 kg/m³. The allometric value b indicated that hatchery‐raised, cage‐cultured snapper were heavier than their wild counterparts. The major costs were feed (ranging from 44.7–45.9%), labor (22.4–32.6%), and seed costs (20.2–26.1%). The total production cost ranged from US$ 6.5 to US$ 7.5/kg. The baseline scenario was not economically feasible. However, a 10% increase in the sales price resulted in increases in the internal rate of return (183%) and net present value (US$ 97,628.9). These results suggest that L. guttatus has the potential for commercial production in cages.     

Experiments for the production of hybrid striped bass in in-pond circulation systems

Experiments for the production of hybrid striped bass (HSB) in in-pond circulation systems (IPCS) were carried out in 2003 and 2004. The circulation system consisted of two channels with a productive volume of 8.5 cubic meters each. The tanks were installed tightly in a pond, which served for the biological cleaning of the expiry water. In the first year HSB fingerlings with an average weight of 46.4 g were produced. The average yield in the basin was 51.2 kg/m³. The survival rate from stocked 0.44 g advanced fry was 97.8%. The food conversion was 1.16. In 2004 two-year-old HSB were reared in the same IPCS. The tanks were stocked at two different stocking densities, 122 and 244 fingerlings/m³ with a mean weight of 36.5 g. In the tank with the larger stocking density, the yield was almost exactly twice as high as in the other tank (50.0 resp. 24.8 kg), which corresponded to a stocking density of 59.1 or 29.3 kg/m³ at the end of the rearing season. The stocking density had no influence on the increase of the individual body weight. Obviously HSB can therefore still be reared at higher stocking densities.     

Effects of Different Feed Habituation Methods on Survival and Feed Habituation Success of Largemouth Bass,Micropterus salmoides,in a Recirculating Aquaculture System

Demand for food size and trophy largemouth bass, Micropterus salmoides, is steadily increasing. However, largemouth bass, a carnivorous species, are more difficult to feed habituate than other commercially produced fish. Improving current feed habituation techniques to increase the percentage of fingerlings successfully feed habituated would increase profits, productivity and efficiency, and available product in the largemouth bass industry. The focus of this research was to evaluate different combinations of automatic feeders and supplemental hand feeding to determine the feed habituation success under commercial largemouth bass production conditions. Hand feeding, using only automatic feeders, or combinations of both, did not result in significant differences with regard to survival or feed habituation success. Initial fingerling size (total length, TL) was found to be the most important factor affecting survival and feed habituation success. Fish ranging from 40 to 50 mm (TL) survived and feed habituated at significantly higher rates than 30–40 and 50–60 mm (TL) fingerlings. Medium‐sized fish provide the best results in terms of feed habituation success and survival. The results suggest any combination of hand feeding and automatic feeders may be used to achieve feed habituating success in largemouth bass.     

Survival rates of tilapia, Oreochromis spilurus (Günther), fingerlings reared at high densities during winter using warm underground sea water

The study was conducted to determine the optimum stocking density for rearing tilapia. Oreochromis spilurus (Günther), fingerlings in tanks during winter using warm (21-26°C) underground sea water (37%o). Seawater-acclimated fingerlings with mean weight of 2 g were stocked in eighteen 400-1 fibreglass tanks at 750 and 1000 fish m^?3. Fish were fed at the rates of 2.5, 3.0 and 3.5% day^?1 of the fish biomass. After 83 days, the mean individual daily weight gain was significantly higher (P < 0.028) at stocking of 750 fish m^?3 than at 1000 fish m^?3. Feed conversion ratio was significantly higher at stocking of 1000 fish m^?3 than at 750 fish m^?3 and at feeding rate of 3.5% day¹ than at 2.5% day^?1. However, because no significant differences were observed on survival rates between the two stocking densities and among feeding rates, it is recommended that the stocking density of 1000 fish m^?3 and a feeding rate of 2.5% day^?1 be used for optimum production of tilapia fingerlings in tanks during winter using warm underground sea water.     

Effect of Stocking Rate on Growing Juvenile Sunshine Bass,Morone chrysops × M. saxatilis,in an Outdoor Biofloc Production System

The biofloc technology production system is a production‐intensifying management strategy used primarily for culturing tilapia and penaeid shrimp, both of which can consume the biofloc. Other fish can be grown in biofloc systems because the biofloc serves to maintain water quality, metabolizing the ammonia excreted by intensively fed fish. A dose–response study was conducted in an outdoor biofloc system to begin quantifying the stocking rate production function for sunshine bass, Morone chrysops × Morone saxatilis, advanced fingerlings. Sunshine bass (2.9 ± 0.2 g/fish) were stocked into tanks at 50–250 fish/m² in 50 fish/m² increments. After 94 d, gross yields ranged from 1.4 to 3.1 kg/m³ and were independent of stocking rate. Harvested fish were separated into two size groups: smaller than 115 mm total length (TL, target fish) and larger than 115 mm TL (jumper fish). Target fish increased linearly from 62 to 93% and jumpers decreased linearly from 38 to 7% of the population, respectively, as stocking rate increased. The outdoor biofloc system offers potential for intensifying the production of advanced sunshine bass fingerlings, but feed consumption appeared to be impeded by high total suspended solids concentrations. Further research is needed to optimize stocking rates and solids management.     

Effect of Stocking Density on Growth and Water Quality for Largemouth Bass Micropterus salmoides Growout in Ponds

Juvenile largemouth bass Micropterus salmoides , trained to accept artificial diets, were stocked into six 0.04-ha ponds at stocking densities of either 6,175 or 12,350 fish/ha. Fish were fed a floating custom-formulated diet, containing 44% protein, once daily to satiation for 12 mo (May 1994–May 1995). At final harvest, the total yield of fish was significantly greater (P < 0.05) and feed conversion ratio (FCR) was significantly lower, for bass stocked at the higher density (4,598 kg/ha and 2.3, respectively) than when stocked at the lower density (2,354 kg/ha and 3.3, respectively). There was no significant difference (P > 0.05) in average weight, length, or survival of bass stocked at the two densities. Averaged over the study period, there were no significant differences (P > 0.05) in total ammonia-nitrogen (TAN), nitrite-nitrogen, or un-ionized ammonia concentrations in ponds in which bass were stocked at the two densities. These data indicate that largemouth bass of the size used in this study are amenable to pond culture at densities of at least 12,350 fish/ha and that higher stocking densities may be possible.     

Effects of stocking density on growth, yield and profitability of farming Nile tilapia, Oreochromis niloticus L., fed Azolla diet, in earthen ponds

Two consecutive experiments were conducted to study the effects of stocking density on growth, food utilization, production and farming profitability of Nile tilapia (Oreochromis niloticus) fingerlings (initial mean weight: 16.2 ± 0.2 g) fed Azolla, as a main component in diet. In experiment 1, fish were hand‐fed twice daily with three isonitrogenous (28.5% crude protein) and isocaloric (14.5 kJ g⁻¹) diets A30, A35 and A40 containing 30%, 35% and 40%Azolla, respectively, for 90 days. Diets were formulated by mixing Azolla with locally available by‐products. No significant differences were found in growth parameters and production (P>0.05). Total investment cost was significantly higher with A30 (P<0.05), but same profitability values were obtained with all diets (P>0.05). In experiment 2, three stocking densities, 1, 3 and 5 m⁻², were assigned to three treatments T₁, T₂ and T₃ respectively. Fish were hand‐fed twice daily with diet A40. The final mean weight (89.53–115.12 g), the mean weight gain (0.81–1.10 g day⁻¹), the specific growth rate (1.90–2.20% day⁻¹) and the apparent food conversion ratio (1.29–1.58) were affected by stocking density, with significant difference (P<0.05) at 5 m⁻², compared with the other densities. Stocking density did not affect survival rate (P>0.05). Yield and annual production increased with increasing stocking density, ranging from 7.10 ± 0.90 to 25.01 ± 1.84 kg are⁻¹ and 28.79 ± 3.66 to 101.42 ± 7.48 kg are⁻¹ year⁻¹, respectively, with significant differences between all densities (P<0.05). Higher stocking density resulted in higher gross return and lower cost of fish production, with significant variations (P<0.05). The net return increased with increasing stocking density (P<0.05). However, both densities of 3 and 5 m⁻² produced the same profitability values. On the basis of growth values and economic return, it was concluded that Nile tilapia could be raised at a density of 3 fish m⁻² with A40 to improve production and generate profit for nutritional security and poverty alleviation in rural areas.