Production of Nile Tilapia Oreochromis niloticus and Freshwater Prawn Macrobrachium rosenbergii Stocked at Different Densities in Polyculture Systems in Brazil

Abstract.— The effect of stocking prawns Macrobrachium rosenbergii at increasing densities in ponds with Nile tilapia Oreochromis niloticus reared at low density was evaluated. Twelve 0.01-ha earthen ponds were stocked with 1 tilapia/m² and 0, 2, 4, or 6 postlarvae prawn/m². Three replicates were randomly assigned to each prawn density. Postlarval prawns were stocked a week prior to tilapia juveniles and both were harvested 175 d after the beginning of the experiment. Tilapia final average weight, survival, production, and food conversion rates did not differ significantly among treatments ( P > 0.05); the averages were 531 g, 67%. 3,673 kg/ha, and 1.91, respectively. Prawn survival rates did not differ for the three stocking densities (mean 90%). However, final weight and production were significantly different ( P < 0.05) as follows: 34.0, 23.0, and 14.7 g and 639, 909, and 818 kg/ha, respectively for 2. 4, and 6 prawns/m² densities. Stocking densities up to 6 prawn/m² did not affect tilapia production and required neither additional feeding nor significant changes in management. The polyculture system allowed an increase in total production with the same amount of supplied feed, thus improving the system sustainability.     

Growth, Survival, Yield, and Size Distributions of Freshwater Prawn Macrobrachium rosenbergii and Tilapia Oreochromis niloticus in Polyculture and Monoculture Systems in Puerto Rico

Abstract.— Tilapia and freshwater prawn production in Puerto Rico for monoculture and polyculture systems were compared. The experiment consisted of three treatments with three replicates each. The stocking rates for the prawn monoculture, fish monoculture and polyculture treatments were respectively: 7 prawns/m², 1 tilapia/M², and 7 prawns with 1 tilapia/ m². The mean stocking size for tilapia and prawn were respectively, 7–8 g and 1–1.3 g. After 145 d of culture, yields and mean weight of tilapia in monoculture and polyculture system were not significantly different. Total yields were 2,942 and 2,769 kg/ha, respectively. Mean weights were 348 g in monoculture and 331 g in polyculture. Yields and mean weight of prawns in monoculture and polyculture were significantly different. Total yields were 1,367 and 951 kg/ha, respectively. Mean weights were 55 g in monoculture and 31 g in polyculture. Total yield in polyculture was 3,720 kg/ha showing an increase over the production separately obtained in prawn and fish monoculture.     

Growth Response and Resistance to Streptococcus iniae of Nile Tilapia, Oreochromis niloticus, Fed Diets Containing Distiller's Dried Grains with Solubles

This study was conducted to evaluate the effect of dietary levels of distiller’s dried grains with solubles (DDGS) on growth, body composition, hematology, and resistance of Nile tilapia, Oreochromis niloticus, to Streptococcus iniae challenge. Five isocaloric diets containing DDGS at levels of 0, 10, 20, and 40%, and 40% DDGS + lysine (Diets 1–5) as partial replacements of a combination of soybean meal (SBM) and corn meal (CM) on an equal protein basis were fed to juvenile Nile tilapia (9.41 ± 0.14 g) for 10 wk. Fish fed Diet 4 had the lowest weight gain (WG), feed efficiency ratio, protein efficiency ratio (PER), and whole‐body protein. Supplementation of lysine to the 40% DDGS diet (Diet 5) improved WG and PER. Hematological and immunological parameters were not affected by dietary treatment. There were no significant differences among the average number of days to first mortality after S. iniae challenge and cumulative mortality 14 d postchallenge among fish in various treatments. DDGS can be incorporated in tilapia diet at a level of 20% as a substitute for a combination of SBM and CM without affecting their growth performance, body composition, hematological parameters, immune response, and resistance to S. iniae infection.     

Evaluation of Distillers Dried Grains with Solubles as an Ingredient in Diets for Pond Culture of the Freshwater Prawn Macrobrachium rosenbergii

Distillers dried grains with solubles (DDGS) were evaluated as an ingredient in practical diets for pond culture of the freshwater prawn Macrobrachium rosenbergii . Juvenile prawns averaging 0.66 ± 0.47 g were stocked into nine 0.02 ha ponds at 19,760/ha. Three isonitrogenous diets (29% crude protein) containing 0, 20, or 40% DDGS were fed to shrimp in triplicate ponds. Average yield, survival, individual weight, and feed conversion did not differ significantly ( P > 0.05) among treatments. When averaged over the three diets, results were: yield, 833 kg/ha; survival, 75%; individual weight, 57 B; and feed conversion, 3.1. It appears that DDGS is a suitable ingredient for use in practical diets for freshwater prawns at levels of up to 40% of the total formulation, when prawns are stocked at the densities used in this study.     

Growth, Survival, and Biochemical Composition of Freshwater Prawns Macrobrachium rosenbergii Fed Natural Food Organisms Under Controlled Conditions

Under production conditions freshwater prawns Macrobrachium rosenbergii are supplied nutrients by a combination of prepared diets and natural pond organisms. For maximum production efficiency and profitability it is important that the nutritional contributions of natural foods be identified and quantified. In this study the relative importance of forage organisms previously identified as important natural foods for prawns in ponds were evaluated under controlled conditions. Juvenile prawns (average weight 1.80 ± 0.06 g) were stocked into 18 37.5-L aquaria at a density of 10 prawns per tank. The six dietary treatments tested were: 1) unfed (negative control); 2) commercially prepared diet (positive control); 3) oligo-chaetes; 4) chironomids; 5) zooplankton; and 6) a combination of the latter three. Each treatment was evaluated in triplicate aquaria for 7 wk. The growth rate of prawns in the unfed treatment was statistically lower than in fed treatments ( P < 0.05). There were no significant differences ( P > 0.05) between growth rates and survivals among prawns in the five fed treatments. Selective retention of arachidonic acid (20:4n-6), eicosapentanoic acid (22: 5n-3), and docosahexanenoic acid (22:6n-3) in unfed prawns likely indicates the relative nutritional importance of these fatty acids. Comparisons of whole-body fatty acid and amino acid concentrations of prawns and food organisms indicate that zooplankton and oligochaetes may have the most appropriate biochemical compositions as prawn food sources.     

Phosphorus Budget in Integrated Multitrophic Aquaculture Systems with Nile Tilapia,Oreochromis niloticus,and Amazon River Prawn,Macrobrachium amazonicum

Integrated multitrophic aquaculture (IMTA) systems are designed mainly for efficient use of resources. Substrates added to aquaculture ponds provide space for periphyton to settle and recover nutrients, making these nutrients available to the species being reared. The present study is centered on the phosphorus budget, analyzing the main ecological compartments of IMTA systems in earthen ponds stocked with Amazon River prawn, Macrobrachium amazonicum, and Nile tilapia, Oreochromis niloticus, with or without different added substrates. The experimental design was completely randomized, with three treatments (without a substrate, with a geotextile fabric substrate, and with a bamboo substrate) and four replications. Phosphorus entered the systems mainly in tilapia feed (ca. 50–61%), inlet water (ca. 17–27%), and fertilizer (ca. 6–7%). Input of phosphorus from other compartments ranged from 1.5 to 1.9%. Most phosphorus was accumulated at the pond bottom as sediment (ca. 60–68%) and fish biomass (ca. 18–26%), or discharged in the outlet water (ca. 7–10%). Feeding is the main driver for the distribution of phosphorus in the ponds. Levels of phosphorus retained in reared animals (20–28%) were higher in these IMTA systems than in tilapia and prawn monocultures (reported as 10–20% and 10–13%, respectively). Nonetheless, the present data showed that the addition of different types of substrates might not improve the recovery of phosphorus in animal biomass as initially supposed. Even so, these IMTA systems decreased the amount of phosphorus released in effluents, and this decrease was enhanced by the addition of substrates, reducing the impact on the receiving waterbodies.     

Production of Australian Red Claw Cherax quudricarinatus in Polyculture with Nile Tilapia Oreochromis niloticus

Abstract— Australian red claw crayfish Cherax quudricarinurus were cultured in monoculture and in polyculture with male Nile tilapia Oreochromis niloricus in nine 0.02-ha earthen ponds. Red claw with an average weight of 7 g were stocked in all ponds at 2/ m². Tilapia with an average weight of 19 g were stocked in six ponds at either 0.5 or 1/m². A sinking 32% fish diet and dry alfalfa hay was provided to all ponds as feed and forage. After 135 d, red claw survival was similar (19–24%) in all treatments while average weights were 76 g in monoculture and 48 g in both polyculture treatments. Lower than expected survival was a result of stress caused by poor shipping conditions. Tilapia survivals were similar (84–90%) in all ponds and had an average weight of 403 g when stocked at 1/m² and 444 g when stocked at 0.5/m². Red claws are generally considered non-aggressive, especially when compared with other clawed crustaceans. This lack of aggressiveness is suggested as a cause for decreased growth in polyculture with tilapia.     

混养鲫鱼对罗氏沼虾种虾培育效果的影响

在3口面积各为0.3 hm^2、深度2.0 m的长方形池塘(1#、2#、3#)中放入体长0.7～0.8 cm的罗氏沼虾"南太湖2号"无特定病原种虾,密度为3.0×10~5尾/hm^2;养殖30 d时,2#、3#池塘分别混养质量3～4 g/尾的鲫鱼450、900尾,1#池塘不混养作对照组。经过近110 d的培育,1#、2#、3#池塘"南太湖2号"种虾的平均体质量分别达18.36、18.95、22.6 g,收获量分别达931.5、898.4、842.95 kg,饵料系数分别为1.36、1.53和1.71。试验结果表明,罗氏沼虾"南太湖2号"种虾培育池塘混养合理密度的鲫鱼,虽然影响种虾养殖产量,饲料系数增大,但培育出的种虾个体较大,饱满度较高,作为亲本可以为后期育苗工作的顺利开展打下良好基础。     

Growth Performance,Biochemical Responses,and Skeletal Muscle Development of Juvenile Nile Tilapia,Oreochromis niloticus,Fed with Increasing Levels of Arginine

Tilapia, Oreochromis niloticus, is among the fish species with high potential for aquaculture in intensive farming, and Brazil is among the largest producers worldwide. Some of the amino acid requirements in practical diets for tilapia are still unknown. Thus, this study determined the dietary arginine requirements for Nile tilapia juveniles based on growth performance, hematological and biochemical responses, and muscle growth. Three hundred Nile tilapia juveniles (2.95 ± 0.79 g) were distributed into 20–500 L fiberglass aquaria and fed five extruded isoproteic (28% crude protein) and isoenergetic (3160 kcal/kg) diets formulated to contain 0.95, 1.10, 1.25, 1.40, and 1.55% arginine. Based on the quadratic regression analysis, the best results in weight gain, feed conversion, protein efficiency ratio, and protein retention were estimated in fish fed diets containing 1.36, 1.34, 1.36, and 1.37% arginine, respectively. The best amino acid body retention values were estimated in fish fed diets containing 1.31–1.37% arginine. Muscle growth occurred mainly by hyperplasia in fish fed 0.95% arginine, whereas reduction in the hyperplasia time and signs of hypertrophy occurred in fish fed 1.10–1.55% arginine diets. It was concluded that a diet with 1.36% of arginine (with 1.53% lysine in diet) meets the requirements of Nile tilapia juveniles.     

Growth and Body Composition of Nile Tilapia,Oreochromis niloticus,Fry Fed Organic Diets Containing Yeast Extract and Soybean Meal as Replacements for Fish Meal,with and without Supplemental Lysine and Methionine

Quantities of fish meal (FM) have remained level for the past several decades; however, demand has dramatically increased because of its inclusion in all animal production as a high‐quality protein source. Soybean meal (SBM) is the most widely used plant‐protein ingredient for replacing various proportions of FM in aquatic animal diets. However, use of SBM as the sole protein source has often resulted in reduced fish growth. There is a growing segment of consumers who desire organically grown seafood, and tilapia is one of the most‐cultured fish in the world. As tilapia have herbivorous/omnivorous feeding habits, tilapia fed organic diets may allow producers to enter this rapidly developing market. A feeding experiment was conducted to evaluate the combination of organic SBM and an organic yeast extract (YE) as complete replacements for FM in Nile tilapia, Oreochromis niloticus, fry diets. Nine diets were formulated to contain various percentages of organic YE (0, 15, 30, and 45%) in combination with organic SBM (84–34%) with and without amino acid (methionine and lysine) supplementation. At the conclusion of the study, fry fed a control diet containing 20% FM and fry fed a diet containing 45% YE/36%SBM with amino acid supplementation showed no significant differences (P > 0.05) in final weight, weight gain, and specific growth rate (SGR) compared to those fed all other diets. On the basis of these data, an organic diet which replaces FM with a combination of SBM and YE with added methionine and lysine is commercially feasible and further investigation into the increased use of these two ingredients as protein sources in aquaculture diets is warranted.     

Offspring Growth in a Diallel Crossbreeding with Three Strains of Nile Tilapia Oreochromis niloticus

Abstract— A complete diallel crossing of three strains, Stirling, Korean and Local, was used to evaluate heterosis of intraspecific crossbreeding on early growth of Nile tilapia Oreochromis niloticus . All possible F-1 hybrid offspring were obtained and their growth rates to 90 d were compared. The specific heterosis for F-1 hybrids in Stirling × Korean, Stirling × Local and Korean × Local crosses were 7.61, 5.63 and 7.70 for weight, and 0.47, 0.26 and 0.55 for length, respectively. The purebred Stirling strain showed better growth than the other two strains (P < 0.05). When growth of F-1 hybrids was compared between sexes, males grew more rapidly than females (P < 0.05). However, no differences were observed in growth of male or female between hybrid groups. Purebred males in the Stirling strain were slightly heavier than those in the Korean and Local strains, and Local × Stirling, Korean × Local and Local × Korean crosses. However, in purebred females Stirling was superior to Korean, but not the Local strain and all F-1 hybrid crosses. Implications to choose the appropriate strains for developing a breeding program of tilapia are also discussed.     

泼洒糖蜜对池塘养殖罗氏沼虾生长和水质的影响

将单口面积1.33~2.33hm~2、环境相似的6口罗氏沼虾养殖池塘分为2组,3口池塘投喂蛋白质水平为35.4%的饲料,且每日适量泼洒糖蜜(试验组),3口池塘投喂蛋白质水平为41.9%的饲料,不泼洒糖蜜(对照组),常规管理。养殖期间,每隔15d取水样检测氨氮和亚硝态氮含量。156d的饲养结果表明,对照组和试验组罗氏沼虾的产量分别为6600kg/hm~2和6427.5kg/hm~2,降低饲料中的蛋白水平结合泼洒糖蜜不影响罗氏沼虾的生长(P0.05),养殖效益亦无显著差异(P0.05)。但试验组池塘水中氨氮较对照组低54.0%,亚硝态氮低21.0%,泼洒糖蜜显著降低了池塘氨氮和亚硝态氮含量(P0.05)。     

Innovative Egg Custard Formulation Reduced Rearing Period and Improved Survival of Giant Freshwater Prawn,Macrobrachium rosenbergii,Larvae

This study was conducted to determine the performance of new egg custard formula to replace Artemia sp. on the growth and survival of the giant freshwater prawn, Macrobrachium rosenbergii, larvae. Five experimental diets were tested with triplicate treatments: ART (Artemia sp.), ART‐MIX (Artemia sp. + egg custard MIX: a mixture of shrimp, squid, and bivalve meal‐based egg custard, with palm oil), ART‐PBM (Artemia sp. + PBM, poultry byproduct meal‐based egg custard with fish oil), egg custard MIX only, and egg custard PBM only. All experimental diets were tested after 9 d (stage VI) of feeding Artemia sp. to prawn larvae. The stocking density was set at 100 larvae/L in a clear water tank culture system. Results indicated that the highest survival was recorded in the treatment of ART‐PBM (46.07 ± 0.84%) and the lowest was in the MIX treatment (8.87 ± 0.51%). ART‐PBM and ART‐MIX diets successfully reduced the rearing period and improved survival from larval to postlarval stage by 19 and 65%, respectively, compared with the ART diet. However, the use of MIX and PBM alone increased the rearing period up to 11%. The feeding regime of ART‐PBM and ART‐MIX has provided nutritional advantages and can be successfully practiced in the hatchery of M. rosenbergii larvae. The innovative approach of using PBM and palm oil in the egg custard formulation in this study can provide prawn hatchery operators with more options in terms of dietary ingredients and cost‐effective solutions.     

Effects of Stocking Size and Density of Tilapia on Macrobrachium rosenbergii in Polyculture

Studies were conducted to determine the effect of stocking size and density of prawns in polyculture.
In one experiment, postlarval prawns (av. wt. 0.02 g) were stocked in six 0.02 ha earthen ponds at 35,00O/ha. Two ponds were stocked with tilapia fry (av. wt. 0.14 g) and two were stocked with tilapia fingerlings (av. wt. 30.1 g), each at 10,000/ha. Two control ponds had no tilapia. Tilipia stocking size had no effect on prawn growth. Mean weight of prawns after 70 days of culture ranged from a low of 4.5 g when cultured with tilapia fingerlings to a high of 6.6 when cultured in monoculture. Prawn survival was adversely affected by tilapia fry. Average prawn survival in tilapia fry ponds was 65% compared to 75% and 91%, respectively, in tilapia fingerling and monoculture ponds.
In a second experiment, postlarval prawns were stocked in nine 0.02 ha earthen ponds at 40,000/ ha. Six ponds were stocked with 30 g tilapia fingerlings, three at 5,000/ha and three at 15,000/ha. Three control ponds received prawns only. After 100 days of culture, prawn weight ranged from an average of 15.9 g in monoculture ponds to 11.5 g in polyculture ponds. Survival was highest (93.8%) in low density polyculture ponds. Survival was lowest (85.6%) in prawn monoculture ponds. Tilapia reproduction had a negative impact on shrimp production.     

Effects of Two Densities of Caged Monosex Nile Tilapia, Oreochromis niloticus, on Water Quality, Phytoplankton Populations, and Production When Polycultured with Macrobrachium rosenbergii in Temperate Ponds

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.     

The Effect of Biomass Density,Temperature, and Substrate on Transport Survival of Market-Size Freshwater Prawn,Macrobrachium rosenbergii

Abstract

After harvest, adult prawn are often transported for sales to live markets, such as ethnic Asian outlets, in major urban centers. Poor survival during transportation has hindered development and expansion of these markets. Methodologies to increase survival during transport could contribute to industry viability. Three independent trials were conducted. In the first trial, three biomass densities (25, 50 and 100 g/L) were evaluated in 100-L, open plastic containers aerated with pure oxygen and compressed air. Water quality analyses were performed prior to stocking. After 24 hours in the model transport containers, water quality analysis was conducted and all prawn were removed, determined to be alive or dead, and each group weighed and counted. There was no significant difference (P > 0.05) for prawn survival (overall mean 98%) among the three densities. Concentrations of dissolved oxygen and nitrite were not effected by hauling density (P < 0.05). Total ammonia-nitrogen and un-ionized ammonia-nitrogen concentrations increased (P < 0.05) as biomass densities increased, though values remained within what are considered tolerable ranges. In the second trial, the effect of added substrate and temperature on transport survival was evaluated with prawns stocked at the high density (100 g/L). Two water temperatures (21°C and 26°C) with and without substrate were evaluated in a 2 × 2 factorial with three replicate, 100-L model transport containers per treatment combination (12 containers total). Factorial analysis indicated no significant statistical interaction (P > 0.05) between the presence of substrate and water temperature on any measured variable. The main effects of substrate and temperature were then analyzed separately. The presence or absence of substrate had no significant impact (P > 0.05) on prawn survival. However, temperature had a highly significantly impact (P < 0.01) on survival; prawn survival at 21°C averaged 97% compared to 24% at 26°C. The third trial was a commercial verification trial in which 500 kg of live prawn were transported to New York from Kentucky. These data indicate prawn can be successfully transported at 100 g/L for 24 hours when temperatures are maintained near 21°C. Adding substrate to the transport tank appears to provide no benefit.     

An Economic Analysis of Freshwater Prawn, Macrobrachium rosenbergii, Farming in Mymensingh, Bangladesh

This paper deals with production systems, cost structure, and profitability of freshwater prawn, Macrobrachium rosenbergii, farming in a new area of Mymensingh district in the north‐central part of Bangladesh. In the study area, prawn farming practice is still extensive, and only a few farmers (20%) cultivate semiintensively. The costs and returns of extensive and semiintensive farming systems are compared. All farmers in different farming systems made a profit, with seed and feed dominating variable costs. Considerable variation in production costs and profitability was observed. Based on the Cobb–Douglas production function model, return to scale indicates that there is scope to increase production and income from prawn farms in extensive and semiintensive systems by applying more inputs (i.e., seed, feed, and fertilizer).     

Streptococcus agalactiae Vaccination and Infection Stress in Nile Tilapia,Oreochromis niloticus

Abstract

The stress response following intraperitoneal (IP) injection of a non-adjuvant Streptococcus agalactiae vaccine in cultured warmwater Nile tilapia, Oreochromis niloticus, has not been investigated. Further, little or no information is available on stress following S. agalactiae infection and what effect, if any, vaccination has on susceptibility to infection. The objective of this study was to develop preliminary information on the associations between vaccination, stress, and infection. Blood glucose levels were used to evaluate stress in the fish at different time intervals following vaccination and challenge with S. agalactiae. Blood glucose levels were measured in vaccinates and controls at 0, 2, 6, 24 hours, and 28 days post-immunization (0 hours pre-challenge), and at 2,6, 24,48,72, and 312 hours following challenge with 1.5 × 10⁴ colony forming units (CFU) of S. agalactiae/fish. Significant increases in blood glucose levels were observed only in association with the injection of the vaccine and at 2 hours after injection. After S. agalactiae challenge, both controls and vaccinates had significantly (P < 0.05) higher blood glucose values at 2, 24,48, and 72 hours than at 0 hours. However, blood glucose levels in vaccinates were significantly (P < 0.05) lower than the controls at 24, 48, and 312 hours. Blood glucose levels and mortality of the infected controls were significantly correlated (r² = 0.9236, P = 0.0134). The cumulative mortality of the vaccinates and controls was 10% and 60% after 13 days post-challenge, respectively. The relative percent survival (RPS) was 83.4. Our results indicate that the vaccine was efficacious against S. agalactiae and induced short-term stress in tilapia. These preliminary results also suggested, for the first time, that vaccination may significantly reduce the infection stress associated with S. agalactiae infection in tilapia.     

Methionine Requirement in Practical Diets of Juvenile Nile Tilapia,Oreochromis niloticus

Two feeding experiments were conducted to confirm methionine requirement in practical diets of juvenile Nile tilapia, Oreochromis niloticus. Test diets used in both experiments contained 414 kcal gross energy, 28 g protein, and 5 g lipid per 100 g diet. In the first experiment, seven diets were made using cottonseed meal (CSM), dehulled solvent‐extracted soybean meal (DSESM), and gelatin as intact protein sources. Methionine was added to five of these diets at 0.03 or 0.06% increments to produce methionine levels ranging from 0.33 to 0.57% of the diet. Each diet was fed to four replicate groups of male juvenile Nile tilapia (5.62 ± 0.13 g) in a recirculation system for 8 wk. Broken‐line regression analysis of weight gain indicated that methionine requirement of juvenile Nile tilapia was 0.49% of the diet or 1.75% of dietary protein at cystine level of 0.45% of the diet. The second experiment was designed based on methionine requirement determined in the first experiment and also contained seven test diets. The first six diets contained CSM and DSESM as protein sources. Methionine was added to five of these diets at an increasing rate of 0.06% to produce methionine levels ranging from 0.49 to 0.79% of the diet. In the last diet (Diet 7), a portion of DSESM was replaced by gelatin to reduce methionine level to 0.33% of the diet in order to test whether methionine is limited. Each diet was also fed to four replicate groups of male juvenile Nile tilapia (2.32 ± 0.06 g) in a recirculation system for 9 wk. At the termination of the second experiment, there were no significant differences in terms of weight gain, survival, and feed efficiency ratio (FER) among the fish fed the first six diets. However, weight gain and FER of the fish fed these diets were significantly better than those fed Diet 7, confirming the methionine requirement value as has been determined in the first experiment.     

Dietary Niacin Requirement of GIFT Tilapia,Oreochromis niloticus,Reared in Freshwater

The aim of our experiment was to determine the dietary niacin requirement of genetically improved farmed tilapia (GIFT) tilapia, Oreochromis niloticus, reared in freshwater. Six semi‐purified diets were formulated to contain graded levels of niacin (6.4 [basal diet], 16.8, 36.8, 68.5, 143.8, and 297.8 mg/kg). Each diet was fed to triplicate groups of 30 fish (initial average weight 87.2 ± 3.3 g) for 12 wk in 5.6‐m³ aquaria (r = 1.5 m, h = 0.8 m). Results showed that the weight gain rate (WGR) of the fish increased linearly with dietary niacin levels increasing, but there were no further benefits above 36.8 mg/kg. The niacin concentrations in fish livers were positively correlated with dietary levels of niacin and plateaued when niacin in diet exceeded 84.6 mg/kg. With increasing dietary niacin level, serum high density lipoprotein cholesterol (HDLC) content significantly increased, while serum triacylglycerol (TG) content significantly decreased (P < 0.05). There were no significant differences in serum glucose (GLU) and total cholesterol (T‐CHO) contents in the separate fish groups (P > 0.05). Broken‐line regression analysis showed that GIFT tilapia (87–376 g) require a minimum of 20.4 mg/kg niacin in the diet for maximal growth, and 84.6 mg/kg for the highest liver niacin accumulation.