Effects of partial and complete replacement of freshwater shrimp meal (Caridinea niloticus Roux) with a mixture of plant protein sources on growth performance of Nile tilapia (Oreochromis niloticus L.) in fertilized ponds

Despite the well‐documented herbivorous food habits, commercial feeds for production of Oreochromis niloticus usually contain between 7% and 15% animal protein. However, animal protein feedstuffs are expensive, hence the need to search for cost‐effective alternatives in plant‐protein sources. Such alternatives are probably more effective in semi‐intensive systems where natural pond food forms part of the diet. This study evaluated the performance of O. niloticus after feeding diets in which fresh shrimp meal (SM) was gradually replaced by a mixture of plant‐protein sources in fertilized ponds. Three isonitronegenous (24% crude protein) diets containing 12 (control), 6% and 0% SM were fed to three groups of O. niloticus in four replicates per group for 250 days. Fish were fed daily at 2% body weight and sampled monthly to monitor growth and make feed adjustments. Growth, yields, survival and feed conversion ratio were not significantly different (P>0.05) among treatments. Growth of males was double that of females, while the sex ratio was skewed towards females. Although complete substitution of SM by plant protein did not affect the growth of tilapia, production cost was reduced by 36%. In conclusion, animal protein is not required in diets for production of O. niloticus in fertilized ponds.     

Effect of Using Low-Protein Diets in Semi-Intensive Pond Cage Culture of Tilapia,Tilapia rendalli (Boulenger)

ABSTRACT

An experiment was carried out to determine the effect of using low-protein diets on production of Tilapia rendalli in semi-intensive pond cage culture. This was carried out at Bunda College of Agriculture's fish farm, University of Malawi, where two 200-m² earthen ponds of 1-m depth were used for two months from February 2003 to early April 2003. Each pond had 6 cages of 1 m³ in size stocked with 15 fish, each 4.8 ± 1.2 g average weight and 6.7 ± 0.6 cm average length. Chicken manure was used as the organic manure applied at 500 kg/ha/wk and also acted as a control. All treatments were replicated three times. It was observed that fish growth was higher in the soybean meal-based diet, with final weight of 34.4 g, followed by sunflower cake, with final weight of 23.3 g. The lowest was 14.4 g in the chicken manure only, and cottonseed-based diet had final weight of 19.5 g. These results also agree with the specific growth rate (SGR) that ranged from 2.1%/day in the cages only fertilized with chicken manure to 3.6%/day in the soybean-based dietary treatment. The lowest feed conversion ratio of 1.2 was also observed in the soybean-based dietary treatment. This suggests that the use of lower protein diets that contain soybean would produce better results and may increase yield when combined with fertilization, as evidenced by high fish survival rates of more than 93% in all treatments.     

Mixed feeding schedules in semi‐intensive pond culture of Nile tilapia,Oreochromis niloticus,L.: is it necessary to have two diets of differing protein contents?

Two semi‐intensive grow‐out trials of Nile tilapia, Oreochromis niloticus (L.), each consisting of seven mixed feeding schedules (rhythmic presentation of high and low protein) and two constant, a high‐protein and the other low‐protein feeding schedules, were carried out simultaneously for 60 days. Mixed feeding schedules were achieved, in Trial 1, by alternating the presentation of a high feed ration (H; 2.3% body weight (BW)) with a low feed ration (L; 1.5% BW) of a single diet A (crude protein content 33%), and in Trial 2, by alternating the presentation of diet A with diet B of a relatively low protein content (crude protein content 22%). In both trials, significant improvements in protein utilization parameters, such as apparent protein conversion efficiency and protein efficiency ratio against continuously high protein feeding were obtained because of the adoption of mixed feeding schedules without any significant decline in the growth parameters such as net fish yield or daily weight gain. In both trials, the mixed feeding schedule ensuring 2 days of high followed by 3 days of low protein presentation, viz. 2H/3L of Trial 1 and 2A/3B of Trial 2 performed the best. Improvement in nutrient utilization in both trials was comparable; however, at existing market prices cost saving because of adoption of mixed feeding schedules was greater in Trial 1.     

凡纳滨对虾在半集约化土池养殖模式下的生长特性分析

对虾在不同的环境条件和养殖模式下具有不同的生长特性,这是进行对虾高效养殖管理的重要依据之一。为探明半集约化土池养殖模式下凡纳滨对虾(Litopenaeus vannamei)的生长特性,2009年5～8月,在广东省电白县的滩涂土池半集约化养殖区,对两个半集约化养殖土池(P1、P2)的凡纳滨对虾的生长参数(全长、体长和体重)进行了养殖全过程的采样测量和数据分析。结果表明:(1)两个土池养殖的凡纳滨对虾的体长(L)与体重(W)均呈显著的幂函数关系,分别为(P1)W=0.016 L2.8935(R2=0.989,P<0.01)、(P2)W=0.0127 L3.0292(R2=0.9911,P<0.01);其生长拐点分别出现在第124 d和128 d;(2)对虾全长(QL)和体长呈明显的线性关系,分别为(P1)QL=0.8319 L+0.2577(R2=0.9997)、(P2)QL=0.8679 L-0.0434(R2=0.9977);(3)体长、体重的von Bertallanffy生长方程分别为(P1)Lt=17.6955(1-e-0.0095(t-12.2421))、Wt=65.2846(1-e-0.0095(t-12.2421))2.8935,(P2)Lt=16.8567(1-e-0.0104(t-21.1781))、Wt=66.0607(1-e-0.0104(t-21.1781))3.0292。     

施用芽孢杆菌对滩涂土池养殖凡纳滨对虾数量生长特性的影响

在粤西电白县滩涂土池对虾养殖区设置试验组（养殖过程每10d施用芽孢杆菌,用量103CFU/mL）和对照组（不施菌）,养殖设施与其他管理相同,全程监测凡纳滨对虾（Litopenaeus vannamei）体长、体质量和主要水质因子的变化,研究芽孢杆菌对养殖对虾数量生长特性及生产效益的影响。结果显示,养殖对虾体长和体质量呈幂函数关系,Von Bertallanffy方程可较好拟合其生长关系,体长增长速度呈对数递减趋势,而体质量则为递增,日龄50d前的体长生长速率高于体质量的;试验组对虾的体长和体质量自日龄56d即超过对照组,收获虾的体长、体质量极显著增大,饲料系数降低了41.41%,产量提高了6.07%。结果表明,养殖过程合理施用芽孢杆菌可改善对虾的生长数量性状,降低饲料系数,提高养殖综合效益。     

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.     

Growth and economic performance of Nile tilapia (Oreochromis niloticus L.) fed on three brans (maize, wheat and rice) in fertilized ponds

Nile tilapia (Oreochromis niloticus L.) was fed rice bran (RB), wheat bran (WB) and maize bran (MB) at 1.5% body weight. Fingerlings averaging 14 g were stocked at 19 462 fish ha^?1 in three treatments with six replicates per treatment. Clarias gariepinus was stocked at 250 fish ha^?1 to reduce the density of tilapia fry. Growth and economic performance were compared for 250 days in 0.08 ha fertilized ponds. Fish growth was highest (P < 0.05) in MB and least in RB treatment. Growth in WB treatment was intermediate. Feed conversion ratio in MB and WB treatments was similar (P > 0.05), but significantly higher (P < 0.05) than in RB treatment. Water quality parameters were similar (P > 0.05) among treatments. At retail price of US$ 1.28 kg^?1 fish, returns above both variable and total costs from MB and WB treatments were positive, while those from RB were negative. However, at US$ 1.79 kg^?1 fish, all test‐feeds had positive returns above variable and total costs. In conclusion, MB treatment produced the highest growth, but the highest profitability was obtained in the WB treatment. Under present study conditions, RB was not cost‐effective in the production of O. niloticus. A selling price of US$ 1.79 kg^?1 fish is recommended.     

THE SOCIAL AND ECONOMIC IMPACTS OF SEMI-INTENSIVE AQUACULTURE ON BIODIVERSITY

As a result of the concern and debate about the impacts of intensive aquaculture development on biodiversity, semi-intensive aquaculture is being considered as an alternative. Although the biophysical impacts of aquaculture on biodiversity have been examined, there is only limited understanding of the social and economic impacts of aquaculture on biodiversity, and especially the impacts of the shift from intensive to semi-intensive systems. The purposes of this article are twofold: (1) to identify and discuss the social and economic impacts of aquaculture on biodiversity, and (2) to examine the impacts while moving from intensive to semi-intensive systems. After discussing the findings of our study, we provide some recommendations as to how to minimize social and economic impacts of aquaculture on biodiversity by moving to a lower intensity aquaculture system. The integrated agriculture-aquaculture farming systems, stakeholder involvement in management, and well defined basic rights are aquaculture systems that contribute to conservation of biodiversity.     

Digestive enzyme activity and food ingesta in juvenile shrimp Litopenaeus vannamei (Boone, 1931) as a function of body weight

A study was conducted to evaluate variations of digestive enzyme activities in Litopenaeus vannamei (Boone) reared in commercial ponds under semi‐intensive conditions. Shrimp were collected at each body weight increase of 2 g. As the shrimp grew (2–12 g), significant increases in the activities of lipase and chymotrypsin were observed. The total protease activity decreased from 6 g onwards. Trypsin activity showed a peak at 6 g and amylase activity increased two‐fold after 2 g. Additionally, the stomach contents were analysed microscopically for shrimp between 2 and 10 g. Plant matter contributed above 30% of the total stomach content in 6‐, 8‐ and 10‐g shrimp. Detritus represented 58% and 62% of the total stomach content in 2‐ and 4‐g shrimp, respectively, decreasing to 33–43% at greater shrimp weights. Artificial feed showed a maximum contribution of 20% in 6‐g shrimp. The present results show changes in the enzyme activity after the shrimp reach 6 g in body weight, evidenced by a decrease in total protease and an increase in lipase and amylase activities. The amylase/protease ratio was 2.6 in 2‐g shrimp and increased steadily to 9.6 in 12‐g shrimp. These findings suggest an adaptation of the enzymatic activity to diets with lower protein content as body weight increases, and may be related to the variation of the different items found in the stomach.     

Growth and economic performance of Nile tilapia (Oreochromis niloticus L.) fed on two formulated diets and two locally available feeds in fertilized ponds

Lack of suitable diets for semi‐intensive production of Oreochromis niloticus in Kenya has necessitated use of expensive diets designed for intensive production. To address this problem, two isonitrogenous (24% protein) diets were formulated and evaluated for production of O. niloticus in fertilized ponds. One diet contained vitamins and minerals premix (CV) while the other had no premix (CW). Growth of fish fed on the formulated feeds was compared with groups of fish fed on commercial pig pellets (PP) and wheat bran (WB). There were significant differences in mean weights, growth rates and feed conversion ratios between the formulated and the other diets. No significant differences in these parameters were observed between CV and CW and also between PP and WB. Fish that fed on the formulated feeds produced significantly lower number of juveniles than those fed on PP and WB. Fish fed on WB gave the best economic returns while those on PP had the least returns. Present results suggest that vitamins and minerals premix may not be necessary in diets for semi‐intensive production of O. niloticus. Present results showed that the formulated feeds produced higher yields than PP and WB, but WB had the best economic returns among the test diets.