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1.
A 117‐day feeding trial was conducted in ponds with juvenile Australian red claw crayfish (Cherax quadricarinatus) to evaluate the effects on growth, survival, body composition, and processing traits when fed diets containing three different protein levels (22%, 32%, and 42%), and the effects of feeding these diets on pond water quality. Juvenile crayfish (mean weight of 4.6±2.2 g) were randomly stocked into nine 0.02‐ha ponds at a rate of 500 per pond (25 000 ha?1), and each diet was fed to three ponds. There were two feedings per day, each consisting of one‐half of the total daily ration. At harvest, there were no significant differences (P>0.05) in the individual weight, percentage weight gain, or specific growth rate among treatments, which averaged 75.3 g, 1535%, and 2.38% day?1 respectively. Red claw fed the 42% crude protein diet had significantly higher (P<0.05) feed conversion ratio (7.34) compared with crayfish fed diets containing 22% (5.18) or 32% (5.13) crude protein, and had significantly lower percentage survival (46.1%) compared with red claw fed diets with 22% (61.1%) or 32% (58.2%) protein. Total yield was significantly lower (P<0.05) in red claw fed the 42% protein diet (640 kg ha?1) compared with red claw fed diets containing 22% (920 kg ha?1) or 32% (904 kg ha?1) protein. Mean total ammonia nitrogen (TAN) levels were significantly higher (P<0.05) in ponds with red claw fed the 42% protein diet (0.55 mg L?1) compared with ponds with red claw fed diets containing 22% (0.32 mg L?1) or 32% (0.38 mg L?1) protein. Mean total nitrite concentrations in ponds with red claw fed the 42% protein diet was significantly higher (0.05 mg L?1) compared with red claw fed diets containing 22% (0.01 mg L?1) or 32% (0.02 mg L?1) protein. These results indicate that a practical diet containing 22% (as fed basis) protein may be adequate for pond production of red claw when stocked at the density used in this study, and that a diet containing 42% protein adversely affected levels of TAN and nitrite, possibly reducing overall survival of red claw. Use of a diet with 22% protein may allow red claw producers to reduce diet costs and thereby increase profits.  相似文献   

2.
The effects of different densities of caged Nile tilapia, Oreochromis niloticus, on water quality, phytoplankton populations, prawn, and total pond production were evaluated in freshwater prawn, Macrobrachium rosenbergii, production ponds. The experiment consisted of three treatments with three 0.04‐ha replicates each. All ponds were stocked with graded, nursed juvenile prawn (0.9 ± 0.6 g) at 69,000/ha. Control (CTL) ponds contained only prawns. Low‐density polyculture (LDP) ponds also contained two cages (1 m3; 100 fish/cage) of monosex male tilapia (115.6 ± 22 g), and high‐density polyculture (HDP) ponds had four cages. Total culture period was 106 d for tilapia and 114 d for prawn. Overall mean afternoon pH level was significantly lower (P ≤ 0.05) in polyculture ponds than in CTL ponds but did not differ (P > 0.05) between LDP and HDP. Phytoplankton biovolume was reduced in polyculture treatments. Tilapia in the LDP treatment had significantly higher (P ≤ 0.05) harvest weights than in the HDP treatment. Prawn weights were higher (P ≤ 0.05) in polyculture than prawn monoculture. These data indicate that a caged tilapia/freshwater prawn polyculture system may provide pH control while maximizing pond resources in temperate areas.  相似文献   

3.
Abstract

The effects of renovation on the production of white river crayfish, Procambarus acutus acutus were evaluated in ten 0.1-ha earthen ponds. The bottoms and levees of five ponds were reshaped with heavy equipment prior to planting sorghum-Sudan grass forage during the de-watered phase of the culture cycle. Five non-renovated ponds served as a control. The mean total length (TL) of the crayfish harvested from renovated ponds was significantly larger than those crayfish harvested from non-renovated ponds. The renovated pond harvest contained an estimated 43.2% carryover crayfish (>95 mm TL) in comparison to 7.6% in the harvest from non-renovated ponds. By weight, carryover crayfish constituted an estimated 69.3% of the harvest from renovated ponds, compared to 21.0% from non-renovated ponds. No difference was observed in the harvest between treatments; however, the low proportion of young-of-the-year crayfish in the renovated pond harvest may adversely impact future production.  相似文献   

4.
Previous work suggested that feeding catfish, Ictalurus punctatus, more frequently over the winter might reduce weight loss. Twelve 0.10-ha ponds were stocked with 987 kg/ha market-sized fish and 2,960 kg/ha sub-marketable fish in November 2008 with treatments of: (1) unfed, (2) fed daily (fed 90 d), and (3) temperature-threshold feeding (fed 62 d). Total gross yield was significantly greater for the temperature-threshold feeding treatment than the unfed control, but survival and mean weight of fish at harvest were not. Net yield was negative for all treatments, due primarily to mortality of market-sized fish. Plasma glucose and insulin-like growth factor-1 did not differ significantly, but plasma osmolality was significantly lower in fasted than in fed fish. Mean feed consumption rates in vats provided evidence to support more frequent feeding over the winter. Overwintering costs were $0.11/kg with temperature-threshold feeding. Research on strategies to reduce winter mortality has potential to reduce overwintering costs.  相似文献   

5.
To be profitable, producers must reduce diet costs, which can be as high as 80% of the variable costs of an aquaculture expense. As vitamin and mineral premixes represent a significant cost, eliminating addition of these premixes could reduce diet costs if no adverse effects were observed for growth and production parameters. A 105‐day feeding trial was conducted with juvenile Australian red claw crayfish (Cherax quadricarinatus) to evaluate the effects of growth, survival, body composition, processing traits and water quality when red claw were fed a supplemental diet containing 28% crude protein (CP) without vitamin and mineral premixes (and supplemented alfalfa hay) compared with red claw fed a diet (control diet) containing 42% CP, vitamin and mineral premixes, and with supplemented alfalfa hay, and compared with red claw only fed alfalfa hay when grown in ponds. Juvenile red claw (mean weight of 15.7 ± 1.0 g) were randomly stocked into nine 0.02‐ha ponds at a rate of 640 per pond (3.2 per m2), and each treatment was used in three ponds. There were two feedings per day, each consisting of one‐half of the total daily ration. At harvest, individual weight, percentage weight gain, specific growth rate, survival and total yield of red claw fed a control diet was significantly higher (P < 0.05) (83.0 g, 398%, 1.53% day?1, 65.1%,and 1708 kg ha?1 respectively) compared with red claw only fed alfalfa hay (44.9 g, 202%, 1.04% day?1, 30.3% and 431 kg ha?1, respectively), but not different (P > 0.05) from red claw fed the supplemental diet without vitamin and mineral premixes (76.2 g, 367%, 1.47% day?1, 57.2% and 1378 kg ha?1). There were no significant differences (P > 0.05) in feed conversion ratio (FCR) among treatments, which averaged 5.0 (based on prepared diet input). These results indicate that vitamin and mineral supplementation in a diet is not necessary when diet containing 28% CP and alfalfa hay are used in combination for pond grown red claw. These results may help reduce diet costs and possibly increase producers’ profits which might allow for industry expansion.  相似文献   

6.
The influence of fertilization and of fry stocking density on production of fingering walleye, Stizostedion vitreum, was evaluated in earthen ponds at North Platte State Fish Hatchery, North Platte, Nebraska. In 1990, five 0.4-ha ponds were fertilized with alfalfa pellets, and five were fertilized with soybean meal; four unfertilized ponds served as controls. All ponds were stocked with D2 (Dl = the day at hatch) walleye fry at 250.000ha. Differences in yield, number of fingerlings harvested, mean length, and mean weight amone treatments were not statistically significant (P> 0.05). In 691, two fertilization schedules (no fertilizer and fertilization with alfalfa pellets) and two fry stocking rates (250.000 and 375,000 fry/ha) were evaluated. Four ponds were used for each treatment. Statistically significant treatment differences were found in yield, number of fingerlings harvested/ha, average length, and average weight. Yield was higher in fertilized ponds compared with yield from unfertilized ponds at both stocking densities, but yield did not differ significantly between stocking density treatments given the same fertilizer treatment. Survival did not differ between density treatments, but total number of fish harvested was significantly greater from ponds stocked at the higher density. Fingerlings with the largest average weight were raised in fertilized ponds that were stocked at 250,00O/ha, while the smallest fingerlings were from unfertilized ponds that were stocked at 375,000ka. Days in culture interval, which varied among ponds by 9 days in 1990 and 10 days in 1991, was significantly correlated with most production variables in 1990 and with all production variables in 1991. Means of water quality variables were not significantly different between fertilized and unfertilized ponds in either year, but significant differences were found in means of three water quality variables between 1990 and 1991. Yield in both fertilized and unfertilized ponds in 1991 was less than in 1990.  相似文献   

7.
Stocking and harvest data from 45 grow-outs of the crayfish Cherax tenuimanus (Smith 1912) on a commercial farm were analysed to give predictive equations for survival, mean weight and individual weights of crayfish at harvest. Density dependence was a major factor influencing variation in survival and mean weight. Harvest mean weight decreased, and biomass increased, with density. The crayfish price ($ kg?1) employed to estimate the market value of harvested crayfish increased with individual weight from a minimum saleable weight of 40 g. For grow-out of 0+ year-olds for 1 year, the market value was a maximum at low stocking densities of 1.5-2.0 m?2. Further grow-out for 1 year of the unsaleable weight range (20-40 g) of 1+ year-olds, gave a harvest value which increased with stocking density. Comparison of predicted and actual cohort numbers and mean weights for a further 1 5 harvests showed no bias in prediction and a mean precision level of 16% for numbers and 11% for mean weight.  相似文献   

8.
Production characteristics of pan-size (approximately 227 g) channel catfish (Ictalurus puncturus) were determined in cages and open ponds stocked with fingerlings to densities of 20,000 and 12,500 fish/ha. After 145 days, mean fish weight in all treatments exceeded 227 g. Mean survival was similar in all treatments. Food conversion ratios were significantly better in ponds than in cages but density did not affect the ratios. Neither density nor production system affected production (as measured by total weight produced) when initial density differences were considered (analysis of covariance). Variability in total length at harvest was similar between production systems; however, low density treatments were less variable than high density treatments. Results of this study indicate that pan-size channel catfish can be cultured efficiently at stocking densities well above the 12,500 fish/ha (5,000 fishlacre) generally used when culturing fish to larger sizes.  相似文献   

9.
To quantitatively define relationships among stocking densities, feeding rates, water quality, and production costs for channel catfish, Ictalurus punctatus, grown in multiple‐batch systems, twelve 0.1‐ha earthen ponds were stocked at 8,600, 17,300, 26,000, or 34,600 fingerlings/ha along with 2,268 kg/ha of carryover fish. Fish in all ponds were fed daily to apparent satiation using 32% protein floating feed. Temperature and dissolved oxygen in each pond were monitored twice daily; pH weekly; nitrite‐N, total ammonia nitrogen, and Secchi disk visibility every 2 wk; nitrate‐N, chlorophyll a, total nitrogen, total phosphorus, and chemical oxygen demand monthly; and chloride every other month. The costs of producing channel catfish at different stocking densities were estimated. There were no significant differences (P > 0.05) as a result of stocking density among treatment means of (1) gross or net yields, (2) mean weights at harvest, and (3) growth or survival of fingerlings (24–36%) and carryover fish (77–94%). Mean and maximum daily feeding rates ranged from 40 to 53 kg/ha/d and 123 to 188 kg/ha/d, respectively, and feed conversion ratios averaged 1.75. There were no differences in any feed‐related parameter as a result of density. Water quality variables showed few differences among densities at samplings and no differences when averaged across the production season. Yield of fingerlings increased as stocking density increased with significant differences between the two highest and the two lowest stocking densities. Breakeven prices were lower at the higher stocking densities as a result of the higher yield of understocked fish and similar mean individual fish weights produced at these higher stocking densities. Overall, varying stocking densities of fingerlings in multiple‐batch systems had little effect on production efficiency and water quality. Additional research on managing the population structure of carryover fish in commercial catfish ponds may be warranted.  相似文献   

10.
Previous research showed that stocking 1.5 rohu (Labeo rohita) and 0.5 common carp (Cyprinus carpio) m−2 yields the highest production in small holder ponds in Bangladesh. The present study looked into the effects of additional stocking of Nile tilapia (Oreochromis nilotica) in fed or non‐fed ponds on water quality and fish production. A low, additional stocking density of 0.2 Nile tilapia m−2 was tested. All treatments were executed in triplicate in 100 m2 ponds and the duration of the experiment was 4.5 months. The results showed that tilapia addition increased nutrient concentrations and reduced total suspended solid concentration and phytoplankton biomass (P<0.05). Tilapia stocking resulted in additional production without affecting the growth and production of rohu and common carp. Supplemental feeding increased the nitrogen and phosphorus concentrations, phytoplankton availability and the growth and production of rohu and common carp (P<0.01). The combination of supplemental feeding and tilapia stocking resulted in a higher net yield than the other treatments (P<0.05). Stocking 1.5 rohu, 0.5 common carp and 0.2 tilapia m−2 in fed‐ponds is a good culture combination for polyculture farmers in South Asia.  相似文献   

11.
Catfish farmers increasingly are producing fish larger than the traditional size of 0.45-0.57 kg/fish in order to meet processing plant requirements for larger fish. Production of larger channel catfish Ictalurus punctatus in multiple-batch culture has been investigated in a few studies, but the impact of understocked fingerlings on growth of carry-over fish is unknown. The present study was conducted to quantify growth, feed conversion ratio, net daily yield, and net and total yield of stocker channel catfish grown in single-batch, one-season culture to mean individual weights of 0.60, 0.72, 0.91, or 1.17 kg/fish. Channel catfish (mean weight = 0.26 kg/fish) were stocked into 12 0.1-ha ponds at 11,115 fish/ha. Fish were fed a 32% crude protein floating extruded feed once daily to apparent satiation. When the average weight of the fish population reached the target weight, three randomly selected ponds were harvested. Fish growth was linear in all treatments. Growth rates were similar for fish grown to 0.60, 0.72, and 0.91 kg/fish, and significantly lower ( P < 0.05) than for fish grown to 1.17 kg. Variation in individual fish weight increased linearly with increased duration of culture period. Feed conversion ratio averaged 1.9 and did not differ significantly among treatments. The percentage of the fish population at harvest that fell within the 0.57 to 2.04 kg-size range preferred by processing plants increased from 56.6 to 98-5% as the mean weight at harvest increased from 0.60 to 1.17 kg/fish.  相似文献   

12.
An experiment was conducted in earthen ponds at the Asian Institute of Technology, Thailand to determine different phosphorus fertilizer dose effects on Nile tilapia production, water quality variables, nutrient utilization and cost‐benefit under supplemental feeding. Five phosphorus fertilization rates were used as treatments e.g. 100%, 75%, 50%, 25% and 0% of 7 kg P ha week?1. Nitrogen fertilization rate was fixed at 28 kg N ha week?1 for all the treatments. Sex‐reversed Nile tilapia were stocked at 3 fish m?2, and 30% CP floating feed fed at 50% satiation feeding rate. Nutrient budget showed higher phosphorus fertilizer input resulted in higher phosphorus sink in the sediment. Mean weight, mean weight gain, daily weight gain and net yield were not significantly different among treatments (P > 0.05). Total Kjeldahl nitrogen, total phosphorus and soluble reactive phosphorus were significantly different among treatments. Economic analysis showed phosphorus fertilization resulted in positive net returns. Though the gross income was not affected by different fertilization rates, significantly lowest cost was found in the treatment using 25% phosphorus fertilizer. It can be concluded from the research that 25% phosphorus fertilization might be used as an alternative strategy of Nile tilapia pond culture in terms of economic return and nutrient loss in sediment.  相似文献   

13.
The acocil C. montezumae is a freshwater crayfish endemic to the Central Plateau of Mexico, but, in recent years, the natural population of this species has diminished considerably. In this work was investigated growth performance and feeding of this crayfish reared at high densities. A random block experimental design with two repetitions and three treatments (77, 154 and 231 crayfish/m2) was carried out. Organisms were fed every third day with 15% of their total biomass of shrimp commercial food with 25% of crude protein, and individual food consumption (IFC) was calculated. Significant differences (ANOVA, P < 0.05) were detected in final weight, absolute increase, relative rate of increase, instantaneous rate of increase, yield and survival rate between the densities, with those reared at a density of 77 organisms/m2 reaching the largest sizes. There were no-significant differences (P > 0.05) among treatments in terms of initial weight, specific growth rate and feed conversion l rate.  相似文献   

14.
Australian red claw crayfish Cherax quadricarinatus were cultured in nine 0.02-ha earthen ponds at densities of l/m2, 3/m2 and 5/m2 for 158 d. Average weight at stocking was 3.2 g. All ponds were provided with a combination of hay and corn silage at a rate of 500 kg/ha per month and a commercial crayfish ration fed at 5%, decreasing to 2% of estimated biomass/d during the growing season. Overall survival rate was 72%, and did not differ among treatments. Final yields and average weights varied significantly with stocking density. Red claw averaged 67 g with an average pond yield of 475 kg/ha at l/m2. At 3/m2 and 5/m2, red claw averaged 48 g and 38 g, respectively, and yielded 1,020 kg/ha and 1,422 kg/ha, respectively.  相似文献   

15.
Channel catfish Ictalurus punctatus farming is the largest component of aquaculture in the USA. Culture technologies have evolved over time, and little recent work has been conducted on the effects of stocking density on production characteristics and water quality. Twelve 0.1‐ha ponds were stocked with 13‐ to 15‐cm fingerlings (16 g) at either 8600, 17,300, 26,000, or 34,600 fish/ha in single‐batch culture with three replicates per treatment. Fish were fed daily to apparent satiation with a 32% floating commercial catfish feed. Nitrite‐N, nitrate‐N, total ammonia nitrogen (TAN), total nitrogen, total phosphorus, chemical oxygen demand (COD), Secchi disk visibility, chlorophyll a, chloride, total alkalinity, total hardness, pH, temperature, and dissolved oxygen (DO) were monitored. Ponds were harvested after a 201‐d culture period (March 26, 2003 to October 13, 2003). Net yield increased significantly (P < 0.05) as stocking density increased, reaching an average of 9026 kg/ha at the highest density. Growth and marketable yield (>0.57 kg) decreased with increasing stocking density. Survival was not significantly different among densities. Mean and maximum daily feeding rates increased with density, but feed conversion ratios did not differ significantly among treatments (overall average of 1.42), despite the fact that at the higher stocking densities, the feeding rates sometimes exceeded 112 kg/ha per d (100 lb/ac per d). Morning DO concentrations fell below 3 mg/L only once in a 34,600 fish/ha pond. Concentrations of chlorophyll a, COD, nitrite‐N, and TAN increased nominally with increasing feed quantities but did not reach levels considered problematic even at the highest stocking densities. Breakeven prices were lowest for the highest stocking density even after accounting for the additional time and growth required for submarketable fish to reach market size. While total costs were higher for the higher density treatments, the relatively higher yields more than compensated for higher costs.  相似文献   

16.
Abstract.— A study was conducted to determine the effect of increasing density on growth and size distribution of paddlefish, Polyodon spathula, juveniles reared in ponds. Feed‐trained paddlefish of mean weight (±SE) 25.8 ± 1.1 g were randomly stocked into nine 0.02‐ha ponds at 12,355, 18,533, and 24,710 paddlefish/ha, three replications per treatment. The fish were fed daily in excess of what they would eat for 97 d, beginning with a floating trout diet containing 45% protein and 16% lipid and then transferring to a floating catfish diet containing 32% protein and 4.5% lipid. Survival at harvest was not significantly different (P > 0.05) among treatments and averaged 90%. Mean final weights (±SD) for the low‐, middle‐, and high‐density treatments were 205.2 ± 54.1, 174.8 ± 53.2, and 178.6 ± 51.4 g, respectively. Best‐fit distributions centered on these means were lognormal. The low‐density distribution was significantly different (P < 0.05) from the two higher densities, which were not significantly different from each other (P > 0.05). Paddlefish weight at the minimum target length of 35 cm was estimated to be 100 g by regression analysis. The probability of paddlefish reaching or exceeding 100 g was 90% for the low‐density treatment. For the two higher densities, probabilities were 79 and 78%, respectively. Mean Fulton’s condition factors (FCFs) (±SD) were 250 ± 19, 242 ± 4, and 256 ± 37 for the low‐, middle‐, and high‐density treatments, respectively. The FCF for the middle‐density treatment was significantly lower than for the low‐ and high‐density treatments (P < 0.05), which were not significantly different from each other (P > 0.05). CV, feed conversion ratio, and relative growth were not significantly different (P > 0.05) among treatments and averaged 0.43, 1.50, and 5.45, respectively. Monoculture of paddlefish juveniles in ponds results in a hierarchic size structure when density is at least greater than 12,355 paddlefish/ha. The effect is enhanced with increasing density but becomes asymptotic as density approaches 18,533 paddlefish/ha. Feeding in excess does not ameliorate the effect.  相似文献   

17.
An experiment was conducted to determlne the long-term effects of an all-plant-protein diet on production characteristics (harvest yield, dressing percentage, and body composition) of catfish Ictalurus punctatus taken from top-harvested, multiple-stocked ponds over a 2.5-yr period of continuous production. Fish in eight 0.08-ha ponds were fed an extruded, 32% protein control diet (CON) containing animal and plant proteins, while fish in eight replicate ponds were fed an isonitrogenous diet containing only plant proteins, primarily from cottonseed meal and soybean meal (APP). Diets were fed once dally to apparent satiation during the growing season. Ponds were top-harvested twice per year in the spring and fall and partially restocked after each harvest. CON-fed fish received 13,335 kg of feed during the 2.5-yr period. APP-fed fish received 13,506 kg of feed. Total yields were 5,562 kg of CON-fed fish and 5,840 kg of APP-fed fish; average annual yields were 3,477 kgha per yr and 3,650 kgha per yr, respectively (P > 0.05). Feed conversion ratios, 2.5 for CON-fed fish and 2.6 for APP-fed Ash, did not differ significantly (P > 0.05). Live weights at harvest averaged 529 g (CON) and 481 g (APP), and were not significantly different. Dressing percentages were 59% for fish fed both diets (P > 0.05). APP-fed fish had less (P < 0.05) visceral fat and less (P < 0.05) muscle lipid than CON-fed fish. Results indicate that a lysine supplemented, all-plant-protein diet containing 40% cottonseed meal and 20% soybean meal is suitable for long-term production of channel catfish in earthen ponds and such a diet can reduce the fat content of pond-reared fish.  相似文献   

18.
The present study was conducted to evaluate production management methods to improve overall survival of channel catfish, Ictalurus punctatus, fry to the fingerling stage by incorporating the use of a live, attenuated vaccine against Edwardsiella ictaluri and employing an extended hatchery phase. In this experiment, four treatments were used. In Treatment 1, 10‐d posthatch (PH) fry were vaccinated and then directly stocked into earthen ponds. In Treatments 2 and 3, 10‐d PH fry were sham‐vaccinated (control) and vaccinated, respectively, kept in nursery tanks for 22 d, and then stocked into earthen ponds. Fry in Treatment 4 were sham‐vaccinated at 10 d PH, kept in nursery tanks for 22 d, and then vaccinated prior to stocking into earthen ponds. Mean fingerling yield at harvest ranged from 4716 kg/ha in Treatment 1 to 8112 kg/ha in Treatment 4. Mean individual fish weight ranged from 38.8 g in Treatment 1 to 40.9 g in Treatment 4, and feed conversion ratios (FCR) ranged from 1.15 in Treatment 4 to 1.51 in Treatment 1. Mean survival ranged from 47.5% in Treatment 1 to 73.4% in Treatment 4. In specific comparisons to evaluate the nursery effect (Treatments 1 and 3), yield and overall survival were significantly different (P < 0.05) between these two treatments. In specific comparisons to evaluate the effect of the use of the vaccine (Treatments 2, 3, and 4), overall survival was significantly different (P < 0.05) between Treatment 2 (sham‐vaccinated control with nursery phase) and Treatment 4 (vaccinated at 32 d PH with nursery phase). No significant differences (P > 0.05) in yield, average weight, and FCR were observed between treatments. Results indicate that implementing an extended hatchery phase and vaccination strategy with older fry can improve overall survival of fingerling fish.  相似文献   

19.
Restaurant patrons, particularly in upscale locations, increasingly prefer entrées developed from portions cut from fillets larger than those currently sold by the US catfish, Ictalurus punctatus, industry. A production study evaluated the feasibility of producing the necessary size (1.6 kg) of catfish. Twelve 0.1‐ha earthen ponds were stocked with 0.363‐kg channel catfish at 2500 (low); 5000 (medium); or 7500 (high) fish/ha, with four replicates. Mean individual weight at harvest exceeded the mean target weight (1.6 kg) at the two lower densities, and the minimum target weight (1.36 kg) at the highest density. Percentages of fish (by weight) that did not meet the minimum weight required were: 1, 5, and 18%, in the low, medium, and high density treatments, respectively. Yields were significantly greater at higher densities (P < 0.05). Costs of production at the two higher densities were 4 to 7% higher than in the traditional multiple‐batch system, but increased to 51% at the lowest density. Results demonstrated the biological feasibility of producing channel catfish of a mean weight of 1.6 kg. Economic feasibility depends on (1) the price premium paid and (2) development of a market for fish sizes between current acceptable maximum sizes accepted and 1.36 kg.  相似文献   

20.
Abstract

Two studies were conducted to determine if temporary sequestration of fingerling channel catfish, Ictalurus punctatus, in cages improves production of multiple-crop ponds. In the first study, 0.04-ha ponds were stocked with 295 large (mean weight = 566 g) and 780 fingerling (mean weight = 21 g) catfish. Fingerlings were stocked into cages or open ponds. At 120 days after stocking, fish in cages were released. After an additional 40 days, ponds were clean-harvested to remove large (>500 g) and small (<500 g) fish. In the second study, ponds (0.08-ha) were stocked with 750 large (mean weight = 46 g) and 750 small (mean weight = 20 g) fingerling catfish. Small fingerlings were stocked into cages or open ponds. At 60 days after stocking, fish in cages were released. Market-ready fish were selectively harvested at five and nine months after stocking. Results from the first study indicated that individual weight, weight gain, and yield of both size classes of fish raised in sequestered ponds were significantly greater (P< 0.05) than that of fish raised in open ponds. In addition, total weight gain and yield of fish in sequestered ponds was significantly greater (P< 0.05) than those in non-sequestered ponds. Results from the second study indicated that a significantly greater (P< 0.05) number of market-ready fish were harvested from sequestered ponds than from non-sequestered ponds. Mean yield of sequestered ponds was 31% greater than that of non-sequestered ponds; however, differences were not significant (P> 0.05). Amount of feed fed to fish raised in sequestered ponds was significantly greater (P< 0.05) than amount of feed fed to fish raised in non-sequestered ponds in both studies. It is unclear which factor or factors were responsible for the enhanced production of sequestered ponds; however, temporary sequestration may reduce agonistic behavior and competition for feed between fish size groups.  相似文献   

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