Cage‐pond integration of African catfish (Clarias gariepinus) and Nile tilapia (Oreochromis niloticus) with carps

Cage‐pond integration system is a new model for enhancing productivity of pond aquaculture system. A field trial was conducted using African catfish (Clarias gariepinus) and Nile tilapia (Oreochromis niloticus) in cages and carps in earthen ponds. There were four treatments replicated five times: (1) carps in ponds without cage, (2) tilapia at 30 fish m^?3 in cage and carps in open pond, (3) catfish at 100 fish m^?3 in cage and carps in open pond, (4) tilapia and catfish at 30 and 100 fish m^?3, respectively, in separate cages and carps in open pond. The carps were stocked at 1 fish m^?2. The cage occupied about 3% of the pond area. The caged tilapia and catfish were fed and the control ponds were fertilized. Results showed that the combined extrapolated net yield was significantly higher (P < 0.05) in the catfish, tilapia and carps integration system (9.4 ± 1.6 t ha^?1 year^?1) than in the carp polyculture (3.3 ± 0.7 t ha^?1 year^?1). The net return from the tilapia and carps (6860 US$ ha^?1 year^?1) and catfish, tilapia and carps integration systems (6668 US$ ha^?1 year^?1) was significantly higher than in the carp polyculture (1709 US$ ha^?1 year^?1) (P < 0.05). This experiment demonstrated that the cage‐pond integration of African catfish and Nile tilapia with carps is the best technology to increase production; whereas integration of tilapia and carp for profitability.     

POLYCULTURE OF THE FRESHWATER PRAWN (Macrobrachium rosenbergii) WITH TWO COMBINATIONS OF CARPS IN MANURED PONDS

A study was conducted to 1) evaluate the compatibility of prawns (Macrobrachiurn rosenbergii) with carps, especially the effect of the common carp (Cyprinus carpio); and 2) measure the ability of prawns to utilize the foods available in manured systems. Carps used were the silver (Hypophthalmichthys molitrix), bighead (Aristichthys nobilis), grass (Ctenopharyngodon idella) and common carp (Cyprinus carpio). Four ponds (0.09 to 0.17 ha) were stocked with silver, bighead and grass carps while common carp were stocked in only two ponds. Total fish densities were 8,600/ha where four carps were stocked, but only 6,200/ha when common carp were omitted. Post-larval prawns (wt 0.116 g) were stocked at densities of 17/m². Swine (approximately 60/ha of pond surface area) were housed on pond dikes so that fresh manure continuously entered each pond. Two lots of swine were fattened during the experimental period and loadings of swine manure were calculated based on hog size and feed consumption. Growth periods were 163 days for fish and 107 and 121 days for separate stockings of prawns. Gains in biomass by prawns averaged 714 kg/ha in ponds without common carp and 364 kg/ha in ponds containing common carp. Gains in biomass for both fish and prawns were 3,619 kg/ha (19.8 kg/ha/day) in ponds with common carp and 2,924 kg/ha (18.0 kg/ha/day) in those without common carp. Prawn survival was higher (X = 84.5% vs X = 72.5%), but final average weight of prawns was lower (2.64 vs 5.86 g) in the presence of common carp due to competition for food between common carp and prawns. Competition from carp is believed to have exerted less influence on prawn survival than predation on small prawns by larger, faster-growing prawns.     

Rates of oxygen consumption and ammonia excretion of juvenile Eurasian perch Perca fluviatilis L.

The impact of feeding, fish size (body weight from 18.5 to 56.5 g) and water temperature (20 and 23 °C) on oxygen consumption (OC, mg O₂ kg^–1 h^–1) and ammonia excretion (AE, mg TAN kg^–1 h^–1) was studied in Eurasian perch held in recirculation systems. OC for both fed and feed-deprived (3 days) fish was higher at 23 °C (278.5 and 150.1 mg O₂ kg^–1 h^–1) than at 20 °C (249.3 and 135.0 mg O₂ kg^–1 h^–1; P < 0.01). AEs for both fed and feed-deprived fish were also significantly higher at 23 °C than at 20 °C (P < 0.001). Water temperature and fish size had a significant impact on the oxygen:feed ratio (OFR, kg O₂ kg^–1 feed fed day^–1) and ammonia:feed ratio (AFR, kg TAN kg^–1 feed fed day^–1; P < 0.001). Their average values at temperatures of 20 and 23 °C were 0.17 and 0.19 kg O₂ kg^–1 feed fed day^–1 and 0.009 and 0.011 kg TAN kg^–1 feed fed day^–1, respectively.     

Responses of phosphate solubilizing bacteria to qualitatively different fertilization in simulated and natural fish ponds

The growth of phosphate solubilizing bacteria (PSB) was examined inresponse to pond fertilization with poultry dropping (PD) (12,500 kgha^–1 y^–1), cattle manure (CM) (25,000 kg ha^–1 y^–1), inorganic fertilizer (IF) consisting of urea (10.83 kg ha^–1 y^–1) and single super phosphate (43.52 kg ha^–1 y^–1) and inorganic-organic mixed fertilizers (PD:CM:IF – 1:1:1) in simulated fish ponds under alluvial and laterite soil conditions as well as in natural pondslocated in alluvial soil zone. The high correlation between dissolved oxygenand density of PSB implied the contribution of the latter in the aerobicorganic decomposition. The PSB were maximal in the PD, and minimal in theIF treatments. The distribution pattern of PSB was related to theautochthonous C/N ratio and the N/P ratios of water. Relatively low C/N ratios caused greater abundance of PSB. Increased fish production in PD treatments was clearly due to increased primary productivity and higher zooplankton abundance resulting from nutrient-grazing-detritus-microbial-food chain complex pathways.     

Yield and Economic Efficiency of Green Water in Combination with Supplemental Feeds for Artemia Production in Vietnamese Salt Ponds

We evaluated the combined effects of different green water sources and feed supplements on Artemia biomass production and economic efficiency. A two-factor experiment was set up with two green water types produced from the ratios of nitrogen and phosphorus (N:P = 5 and N:P = 10) in combination with two types of supplemental feed (rice bran or pig manure). After 12 weeks of culture, total Artemia biomass yield with the N:P = 5 treatment (2.29 ton ha^?1 crop^?1) was 14% higher than that with the N:P = 10 treatment (1.97 ton ha^?1 crop^?1), although this difference was not significant (P > 0.05). There was no significant interaction between green water and supplemental feeding treatments for the final yield of Artemia biomass. Comparative cost-benefit analysis showed that the treatment of N:P = 5 combined with pig manure attained a significantly higher net profit and cost/benefit ratio than the other treatments.     

Determination of dosage of Azotobacter and organic fertilizer for optimum nutrient release, net primary productivity and fish growth in fresh water fish ponds

Four experiments were conducted in order to determine the optimum dosageof Azotobacter chroococcum vis-a-vis organic fertilizer(cow-dung) required for optimum pond productivity. Hydrobiological parameters ofpond water, Azotobacter survival (viable counts), netprimary productivity (NPP) and fish growth were monitored. Studies have revealedthat irrespective of the treatments, dissolved oxygen (DO) levels weresignificantly (P < 0.05) lowered on inoculating the ponds withAzotobacter. Alkalinity, O-PO₄,NO₃-N, turbidity, NPP, plankton population and fish growth weresignificantly (P < 0.05) enhanced in ponds inoculated withAzotobacter @ 100.0 ml pond^–1w^–2 in combination with cow-dung @ 10000 kgha^–1 y^–1. At higher or lower dosages offertilizers, the values in most of these parameters remained low. On the otherhand, total kjeldahl nitrogen and NH₄-N increased continuously. Ingeneral, viable bacterial counts decreased with increase in pH, however, therate of nitrogen fixation was not affected. Multivariate analysis of the data revealed a significantpositive correlation of nutrients (Total kjeldahl Nitrogen, NO₃-N andO-PO₄), with NPP and plankton populations. NH₄-N, however,showed a significant negative correlation with DO, NPP and plankton populations.Highest fish biomass and SGR also coincided with the highest NPP and planktonpopulations, revealing that a dose of 100.0 ml pond^–1w^–2 (for 25 m³ ponds) ofAzotobacter along with 10000 kg ha^–1y^–1 of cow-dung appears to be optimum for obtainingoptimum pond productivity and fish yield. Nutrients in the sediment(NO₃-N and O-PO₄) also followed similar trend. On theother hand, organic carbon increased continuously with each increase in thedosage of fertilizers. A decline in fish biomass and pond productivity at higherfertilizer dosages has been attributed to low DO, high NH₄-N and BOD.     

Sedimentation and sediment characteristics in sea cucumber Apostichopus japonicus (Selenka) culture ponds

Annual sedimentation, re-suspension rates and contents of particulate organic carbon (POC), particulate organic nitrogen (PON) and total phosphorus (TP) in the sediment were investigated in two sea cucumber culture ponds at Rongcheng, Shandong Province, China. The results showed that the average flux of total particulate matter in the ponds was 22.1 g m² d⁻¹. The average re-suspension rate of the sediment in the ponds was 81.7%. The re-suspension rates in spring and autumn were higher than those in summer and winter. The mean contents of POC, PON and TP in the sediment of the ponds were 4.4, 0.5 and 0.6 (mg g⁻¹), respectively, and the mean contents of Chlorophyll a (Chl a) and pheophytin in the sediment were 8.1 and 12.1 μg g⁻¹ respectively. The POC, PON and TP contents in the sediment of the ponds increased during the period of sea cucumber aestivation (summer) and hibernation (winter), while they decreased during the feeding periods. The organic matter accumulation rate and the contents of POC, PON, TP, Chl a and pheophytin in the sediment were even lower than those in the pond without sea cucumber (P<0.05). The results demonstrated that sea cucumber culture can effectively stop nutrient accumulation at the bottom of the cucumber culture ponds.     

Effect of Different Feeding Levels of Plant‐ingredient‐based Feed on Fillet Fatty Acid Profile,Carcass Trait,and Sensory Characteristics of Indian Major Carps in Earthen Pond Polyculture

The objective of the present study was to evaluate the effect of plant‐ingredient‐based feeds on fillet fatty acid profiles, proximate composition, carcass traits, and sensory characteristics of three Indian major carps (IMCs), Catla catla, Labeo rohita, and Cirrhinus mrigala, when fed at different levels of their body weight. An experimental feed was prepared with only plant ingredients. The IMCs were fed twice daily at 1.0, 1.5, 2.0, and 2.5% of their body weight for 150 d in 0.06‐ha earthen pond polyculture systems. The maximum growth and best feed utilization was achieved with feeding at 2% of fish biomass in the ponds. Fillet yield and lipid recovery increased significantly (P < 0.05), with increasing feeding level up to 2% of body weight and plateaued thereafter. In fillets, eicosapentaenoic acid (20:5n‐3) and docosahexaenoic acid (22:6n‐3) concentration increased with increasing feeding levels. Carcass traits, sensory characteristics, and consumer acceptance of IMC fillets were not influenced by feeding plant‐ingredient‐based feeds at different feeding rates.     

Olive barb, Puntius sarana (Hamilton) is a potential candidate species for introduction into the grow-out carp polyculture system

The compatibility of olive barb, Puntius sarana (Hamilton) with major carps was studied in grow-out carp polyculture system for one year in a set of nine earthen ponds of 0.08 ha each. Three different species combinations evaluated were Control: catla (Catla catla Ham.), silver carp (Hypophthalmichthys molitrix Valenciennes), rohu (Labeo rohita Hamilton) and mrigal (Cirrhinus mrigala Hamilton) at 0.5:0.5:1:1; T1: catla, silver carp, rohu and olive barb at 0.5:0.5:1:1 and T2: catla, silver carp, mrigal and olive barb at 0.5:0.5:1:1 at combined density of 7500 fingerlings/ha. While survival levels of the carps did not differ significantly in treatments (P > 0.05), silver carp recorded highest survival levels (94–96%) followed by olive barb (87–90%), mrigal (72–74%), rohu (72–73%) and catla (67–69%). The specific growth rate (SGR) and average harvested body weight (ABW) of catla and silver carp did not differ significantly among the treatments revealing their competition with mrigal or olive barb to be minimum. In absence of rohu in T2, both mrigal and olive barb showed higher SGR and ABW revealing minimal competition between these two species, while their lower performance in presence of rohu in Control and T1 indicated inter-specific competition with the latter. Such olive barb–rohu inter-specific competition, however, failed to yield significant effect on growth of rohu as revealed from its non-significant SGR difference in presence and absence of olive barb. The lower FCR (2.54 ± 0.06) and higher treatment biomass production (3418.4 ± 95.0 kg ha^− 1 year^− 1) in T1 with rohu–olive barb combination compared to T2 with mrigal–olive barb (2.84 ± 0.11; 3155.1 ± 104.7 kg ha^− 1 year^− 1) indicated feasibility and advantage of culturing rohu with olive barb rather than mrigal in carp polyculture. Further, similar biomass production in Control and T1 also indicated feasibility of replacing mrigal with olive barb in the grow-out carp polyculture system.     

Effect of using different types of organic animal manure on plankton abundance, and on growth and survival of Tilapia rendalli (Boulenger) in ponds

An experiment was conducted to evaluate the effect of using different types of organic manure on the plankton abundance, and growth and survival of Tilapia rendalli juveniles in ponds. Fish weighing 18.15±0.44 g were stocked into 12, 20 m² ponds at 2 fish m^?2 (40 fish pond^?1). There were three replicate ponds per treatment (chicken manure, cattle manure, pig manure, and no‐manure as a control). After 84 days the T. rendalli in the chicken manure treatment were significantly larger and had higher net annual yields than those in the cattle manure, pig manure and no‐manure treatments. The survival rates were not significantly different across the treatments. Significantly higher amounts of chlorophyll a and higher numbers of zooplankton were found in ponds fertilized with the chicken manure treatment. The overall results obtained in this study suggest that the use of chicken manure produces better results than cattle and pig manure treatments on unfertilized ponds.     

Effects of feeding frequency on metabolism of juvenile walleye

The effects of feeding frequency (1, 2, 3, or 15 times daily) on oxygen consumption (OC, mg O₂ kg⁻¹ h⁻¹) and ammonia excretion, (AE, mg TAN kg⁻¹ h⁻¹) of walleye (Stizostedion vitreum) are described. Walleye were reared at a practical culture density of 35·4 kg m⁻³ in a single-pass system at 23·2°C. Diurnal variation in metabolic rates were related to feeding, not to photoperiod. Minimum OC rates occurred 30 min before the first feeding of the day, which was the longest average time since the last feeding. Metabolic rates increased immediately after feeding. The maximum rates for OC were 36–49% higher than the minimum rates, and 14–22% higher than the 24-h mean rate. Maximum rates for AE were 137–409% higher than the minimum rates, and 39–87% higher than the mean rates. There was a highly significant difference in the mean metabolic rates related to feeding frequency. The mean OC rate for 1 feeding day⁻¹ (222·0 mg O₂ kg⁻¹ h⁻¹) was greater than the mean rates for 2, 3 and 15 feedings day⁻¹. The OC rate for 1 feeding day⁻¹ was 50·6% greater than the rate for 15 feedings day⁻¹ (147·4 mg O₂ kg⁻¹ h⁻¹), the lowest mean rate. Mean and maximum oxygen/feed ratio (OFR, kg O₂ kg⁻¹ feed fed day⁻¹), varied inversely with feeding frequency. The mean ammonia/feed ratio (AFR) was similar for all but the 3 feedings day⁻¹ treatment, but the maximum AFRs for 2 and 15 feedings day⁻¹ were lower than the AFRs for 1 and 3 feedings day⁻¹. AE was directly proportional to OC; the regression equations were highly significant, but specific for feeding frequency.     

Effect of substitution of maize bran with chicken manure in semi-intensive pond culture of Tilapia rendalli (Boulenger)

An experiment was carried out to determine the effect of substituting maize bran with chicken manure on the production of Tilapia rendalli semi‐intensive pond culture. The experiment was carried out at Bunda College of Agriculture's fish farm, University of Malawi, where twelve 20 m² concrete ponds of 1 m depth were used for 3 months from October 2005 to January 2006. A thin layer of soil was spread at the bottom of all ponds to allow growth of natural food. Each pond was stocked with 3 fish m⁻² of 10.71 g average weight. Chicken manure was used as the organic manure applied at 1.6 kg 20 m⁻² and substituted for maize bran by 25%. All treatments were replicated three times. It was observed that fish growth was higher in the 3/4 maize bran+1/4 chicken manure with a final weight of 25.1 g, followed by 1/4 maize bran+3/4 chicken manure with a final weight of 21.6 g. The lowest final weight was 19.3 g in the chicken manure only, but did not differ significantly (P<0.05) from the maize bran treatment, which had a final weight of 19.7 g. This suggests that the use of chicken manure would produce better results and may increase yield when combined with supplementary feed like maize bran evidenced by high survival rates of 80% and above in all treatments.     

Brackishwater carp culture in potentially waterlogged areas using animal wastes as pond fertilizers

In order to assess the possibilities of utilizing drainage effluents (salinity range 5.0–12.5), fish culture experiments were carried out. Experiments on polyculture using cow dung (24 000 kg ha^–1 y^–1) as pond fertilizer were conducted at five different salinity levels (0.3–8.5). Studies have revealed that carp perform well in salinities up to 7.5 and reasonably high fish production has been obtained. Even though the ponds had a high trophic status, higher salinities ( > 7.5) appear to repress fish growth probably due to low dissolved oxygen (DO), high BOD and high NH₄-N. Experiments on monoculture of common carp (Cyprinus carpio) conducted at two different salinity levels (0.3–0.9 and 6.0–7.0) using four different organic fertilizers (cow dung at 24 000 kg and 20 000 kg, poultry at 1500 kg, duck at 6000 kg and sheep/goat at 1500 kg ha^–1 y^–1) have revealed the highest fish growth to be in poultry-treated ponds, followed in decreasing order by duck and sheep/goat wastes. Similar trends in fish production were observed both in fresh- and salt-water ponds. However, fish production was lower in ponds having higher salinities ( > 7.5). Nevertheless, these studies indicated that inland saline waters can be utilized for fish culture. With minor modifications in the existing technology of fish culture in stagnant freshwater fish ponds, animal wastes could be used to fertilize brackishwater fish ponds.     

Utilization of carotenoids from various sources by rainbow trout: muscle colour,carotenoid digestibility and retention

Rainbow trout (Oncorhynchus mykiss) with a mean (sd) weight of 120 (2) g were fed diets supplemented with astaxanthin extracted from the yeast Phaffia rhodozyma (OY1 = 50 mg carotenoids kg^–1 feed, OY2 = 100 mg carotenoids kg^–1 feed), astaxanthin (AX = 100 mg astaxanthin kg^–1 feed) and canthaxanthin (CX = 100 mg canthaxanthin kg^–1 feed) for 4 weeks. Muscle analyses at the end of the experiment indicated a significantly higher carotenoid concentration in the AX group, while CX and OY1 groups were similar in spite of the differences in dietary concentration. The measure of total muscle colour difference (E^* _ab) between initial samples and 4 week ones was higher for the AX fish group but showed no significant difference between OY1, OY2, and CX. The hue and the reflectance ratio (R₆₅₀:R₅₁₀) of fish muscle increased in proportion to carotenoid intake. Digestibility (ADC) of yeast astaxanthin in OY1 and OY2 groups was significantly higher than that in the AX group. Canthaxanthin ADC was about one sixth of that of astaxanthin (AX group). Carotenoid retention in the muscle, expressed as a percentage of carotenoid intake, was higher for the AX group than that recorded for OY1 and OY2. According to ADC, carotenoid retention showed a marked lower value for the CX group. Muscle retentions were similar for astaxanthins from both sources.     

The content of total mercury and methylmercury in common carp from selected Czech ponds

The aim of the present study was to investigate concentrations of total mercury (THg) and methylmercury (MeHG) in the common carp from Czech ponds of Rožmberk, Spolsky, Nezmar, and Velky Bědny. Seven common carps (Cyprinus caprio) from each of the ponds were caught. Muscle tissue, the liver, and the soft and hard roe were used for the tests. Total mercury and methylmercury were found in all the muscle tissue samples examined. Detection limits for total mercury and methylmercury determination methods were 0.001 mg kg^–1 and 0.013 mg kg⁻¹ respectively. Methylmercury levels in the liver and gonads were below the method’s limits of detection. THg and MeHg concentrations in muscle tissues were 0.018–0.063 mg kg^–1 w.w. and 0.019–0.063 mg kg^–1 w.w. respectively. MeHg made up 90–100% of THg in muscle tissues. Total mercury and methylmercury concentrations were significantly (P < 0.05) higher in fish from the Spolsky pond than from the Nezmar pond. MeHg/THg ratios were significantly (P < 0.05) higher in fish from the Rožmberk, Spolsky and Nezmar ponds compared with fish from the Velky Bědny pond.     

Microbial risk assessment of livestock-integrated aquaculture and fish handling in Vietnam

Animal manure has been traditionally used to fertilize fish ponds in Vietnam. While this practice effectively reuses agricultural wastes, high concentrations of pathogenic microorganisms in animal manure raise public health concerns. Working in fish ponds and handling of contaminated fish in unhygienic manner were identified as potential factors of occupational risk. Escherichia coli occurred in numbers <10³ colony forming units (CFU)/100 mL in irrigation water and <10⁴ CFU/100 mL in fish pond water that uses animal manure. Escherichia coli on tilapia skin in numbers were <10³ CFU/100 cm in excreta-based systems and <10¹ CFU/100 cm in feed-based systems, respectively. The study identified direct use of animal manure as major contributors of the fecal contamination of pond water as well as skin of cultured fish. Estimated risks of enteric infection were 100–1000 times higher than the US Environmental Protection Agency acceptable risk. While these risk values are not likely to accurately predict infection rates in Vietnam, they indicate a potential occupational risk in the long term. Therefore, a need for risk mitigation measures was realized for health protection of future generation in agricultural communities.     

大型溞的营养成分分析及其作为渔用饲料原料的潜在利用价值

为了评估大型溞在渔用饲料中的的营养价值,测定了不同季节人工培养的大型溞和夏季污水中大型溞风干样的营养成分与重金属含量。结果显示,各季节人工培养的大型溞水分含量存在显著的季节差异,冬季最高为5.14%,夏季最低为2.51%;夏季污水中大型溞水分含量(9.12%),显著高于人工培养的大型溞。人工培养的大型溞粗蛋白含量为30.93%~50.21%,在不同的季节也存在显著性差异,冬季人工培养、夏季污水中大型溞粗蛋白含量显著高于其他组。大型溞的15种氨基酸含量在各季节中差异显著,冬季最高(36.65%),夏季最低(24.74%);夏季污水中氨基酸含量为41.79%,9种必需氨基酸占22.15%,赖氨酸含量达到3.4%,蛋氨酸的含量为1.14%,苏氨酸含量为2.45%。大型溞粗脂肪含量随季节变化差异显著,冬季最高(18.88%),秋季最低(4.19%),夏季污水与冬季人工培养的大型溞无显著性差异。秋季人工培养的大型溞与夏季污水大型溞必需脂肪酸含量最高,为17%左右,所有大型溞中均没有检测到花生四烯酸和亚麻酸。重金属铬、铜和锌、铅最高含量分别出现在夏季污水、秋季、春季、夏季人工培养大型溞;夏季污水和冬季人工培养大型溞中未检测到铅元素,所有大型溞中均没有检测到镉元素。除铬外,铜、铅、砷和锌的最低含量均出现在夏季污水大型溞中。研究表明,大型溞蛋白质、脂肪营养丰富,而夏季污水大型溞必需氨基酸和必需脂肪酸营养价值普遍高于人工培养的大型溞,且重金属潜在毒性较低,作为渔用饲料蛋白源进行资源化利用的可行性更高。     

Management of stocking density,pond size,starting time of aeration,and duration of cultivation for intensive commercial production of shrimp Litopenaeus vannamei

A dynamic stock model was used for quantification of shrimp production and analysis of alternative management schemes of stocking density, pond size, starting time of aeration, and duration of cultivation for intensive commercial production of the shrimp Litopenaeus vannamei. Databases from Mexican farms were used to calibrate the model. Multiple linear regression models were employed to establish relationships between parameters of the stock model and the management variables. Water quality variables (dissolved oxygen, temperature, and salinity) were complementarily analyzed. The final weight of shrimp was directly related to duration of cultivation and dissolved oxygen, and inversely related to stocking density, pond size, and salinity. There were inverse relationships between the growth coefficient and temperature and dissolved oxygen and between mortality rate and temperature. Dissolved oxygen was significantly related to starting time of aeration. Simple linear regression and an equivalence test indicated that biomass at harvest (after 13 weeks in winter, and 20 weeks in summer) was adequately predicted by using the stock model and the multiple regression models. The highest production (winter, 6900 kg ha⁻¹; summer, 12,600 kg ha⁻¹) were predicted using 60 postlarvae m⁻², small ponds (2 ha), and starting aeration at the first week of cultivation; while the lowest yields (winter, 2600 kg ha⁻¹; summer, 6000 kg ha⁻¹) were obtained using 40 postlarvae m⁻², large ponds (8 ha), and delaying the start of aeration until the fifth week of cultivation. The lowest production was 38% (winter) and 48% (summer) of the highest yield. Using small ponds could be particularly important during winter cycles to increase production, while stocking density and starting time of aeration contributed less. In contrast, pond size played a minor role during summer cycles and stocking density was the most sensitive variable.     

Growth and production of the Amazonian tambaqui in fixed cages under different feeding regimes

Experimental culture of the native Amazonian fish tambaqui, Colossoma macropomum, in fixed cages was carried out over a period of 8 months, in Lake Urubu (Rio Grande do Norte, Brazil), to assess the viability of fixed cage culture of tambaqui and to test the influence of diet on growth rates. Nine synthetic net cages (1 m³) were each stocked with 45-day-old fish (mean weight 3 g; mean total body length 51 mm) at a density of 34 fry m^–3. During the first 2 months of culture, fish were fed a balanced formulated feed on an as-fed basis at the rate of 5% body weight day^–1. During months 3–8 this continued for fish in treatment 1 while those in treatment 2 were fed tropical regional fruits, on a wet weight basis at the rate of 5% body wt day^–1. Fish in treatment 3 were given no supplementary feed. Monthly biometric measurements were made on all fish. Fixed cage fish culture was shown to be a viable and simple technique. Survival in all treatments was 100%. With balanced supplementary feed, production was 14.4 kg m^–3, compared with 4.9 kg m^–3 and 2.1 kg m^–3, respectively, in the treatments where fish were fed with fruits and were not given any supplementary feed.     

Use of egg custard augmented with cod liver oil and Moina micrura on production of freshwater prawn postlarvae

Use of egg custard augmented with cod liver oil (CLO) fed during the day, and of an overnight feed with Moina micrura, were evaluated in terms of its effects on production of freshwater prawn (Macrobrachium rosenbergii) postlarvae (PL). Four levels of CLO (0, 1,3 and 5%) were tested. Significantly higher mean (sd) productions, ranging from 11.27 (1.16) to 13.02 (1.70) PL l^–1, were obtained for larvae fed egg custard enriched with CLO compared with that of 7.83 (1.58) PLl^–1 for larvae fed egg custard without CLO. The development and survival of larval stages were also higher for the CLO diets. The -3 highly unsaturated fatty acid (HUFA) in egg custard increased with increasing CLO level (0–5%). The fatty acid composition of postlarvae reflected the composition of the diet.