The effect of C/N ratio on bacterial community and water quality in a mussel‐fish integrated system

A 30‐day experiment was conducted to evaluate the effect of C/N ratio on water quality and bacterial community in an integrated system comprising one molluscan species (pearl mussel Hyriopsis cumingii) and two fish species (gibel carp Carassius gibelio and silver carp Hypophthalmichthys molitrix) at five C/N ratios (6, 8, 10, 12 and 14). The mussel and fishes were reared in the experimental tanks (400 L), but gibel carp received formulated feed. Water quality in the experimental tanks was analysed on day 0, 10, 20 and 30, and bacterial community in the water column and sediment was analysed on day 30. Total nitrogen, total phosphorus and total organic carbon accumulated in the tanks over time. Ammonia and nitrite decreased with the increase in C/N ratio. Bacterial community in the water column and sediment changed at the phylum and genus levels with the increase in C/N ratio, and the critical C/N ratio causing a functional shift of bacterial community occurred at 10 in water column and 12 in sediment. The increase in C/N ratio benefited the growth of both potential probiotics and pathogenic bacteria. The high C/N ratio enhanced the bacterial functions of chemoheterotrophy and hydrocarbon degradation, but depressed the functions of nitrification and denitrification in the water column and sediment respectively. This study reveals that the C/N ratio can be used as a tool to manipulate the bacterial community and water quality in the mussel‐fish integrated system.     

Sedimentation and Resuspension in Earthen Fish Ponds

Resuspension of particles from pond sediment into the water column may be an important nutrient transfer mechanism in aquaculture ponds. However, the magnitude of sediment re-suspension cannot be determined directly because sediment traps collect particles settling from the water column as well as those re-suspended from the pond bottom. We developed a dilution analysis method to differentiate the magnitude of the two particle source fluxes based upon the concentration of soil-derived elements (Si, Al, and Fe) and water-derived elements (C, N) in material collected by sediment traps placed in earthen ponds. Estimated organic C sedimentation from feed residues and algae was compared with trapped organic C as an independent and approximate measure of resuspension. Resuspension fluxes based independently on analyses of three soil-derived elements and on the estimation of expected C sedimentation were similar and accounted for 60–90% of the total solids flux (121–2,676 g/m² per d) in most ponds sampled. The proportion of total flux that was derived from resuspension in ponds stocked with common carp Cyprinus carpio and tilapia Oreochromis spp . was modeled as a hyperbolic function of fish size and density, with a threshold fish size of 200–300 g. Resuspension flux was conservatively estimated to be equivalent to the daily suspension of a few mm of the pond bottom. These results indicate that sediment resuspension is a major process in carp and tilapia ponds, suggesting that the exchange of nutrients between the sediment and overlying water is intensive.     

Effect of three commercial microbial products on bacterial community in a freshwater fish polyculture system

A 30‐day experiment was conducted to evaluate the effect of three commercial microbial products, Novozymes Pond Plus, Zhongshui BIO‐AQUA and Effective Microorganisms on bacterial community in polyculture tanks stocked with grass carp (Ctenopharyngodon idellus), gibel carp (Carassius auratus) and silver carp (Hypophthalmichthys molitrix). Four treatments were tested. One treatment with no supplementation of the microbial products served as control. In the other three treatments, the microbial products were added at the intervals of 10 days respectively. During the experiment, grass carp and gibel carp were fed with a commercial formulated feed daily. Bacterial count and bacterial composition in water column of the tanks were monitored at the intervals of 3 days, and bacterial composition in sediment was determined at the end of the experiment. Bacterial composition in water column varied with progress of the experiment. Some bacteria from Novozymes Pond Plus and Effective Microorganisms could colonize in the tanks but did not dominate in bacterial community. This study reveals that the competition between the exogenous bacteria and native bacteria might be a factor determining the efficacy of the microbial products in improving water quality.     

Comparative study of water environment variation in the industrial aquaculture system of sea cucumber Apostichopus japonicus

This study investigated the microbial community, water quality, bacterial densities and growth performance in the industrial aquaculture system of sea cucumber Apostichopus japonicus without water exchange. Six treatments were set including, C (control treatment without sea cucumber culturing), S (small individual treatment), B (big individual treatment), Sd (small individual treatment with high density), Ss (small individual treatment adding carbohydrate source) and Sb (small individual treatment adding effective microorganisms). A total of 27916–32236 optimized reads and 564–742 operational taxonomic units (OTUs) were obtained from each samples. The phylum Proteobacteria, Actinobacteria, Bacteroidetes and Cyanobacteria predominated, representing 69.01–97.21% of the bacterial communities in the water samples. Cluster analysis and principal component analysis (PCA) showed that higher similarity was observed among S, Sd, Ss and Sb. The densities of TB and Vibrio in Ss were significantly higher than those in the other culture treatments after the 7th day. The concentrations of NH₄‐N, NO₂‐N, NO₃‐N and PO₄‐P in Ss and Sb were relatively lower than the other treatments. Conclusively, no deterioration was found in the water environment parameters during the 21‐day culture period without water exchange, indicating that low‐level water exchange protocol may be applied to the industrial aquaculture system. Based on the effects of different operations on culture system, industrial aquaculture is proved to be a viable way to rear sea cucumber.     

Viability of a Freshwater Mussel (Elliptio complanata) as a Biomechanical Filter for Aquaculture Ponds II: Effects on Aquaculture Pond Water Quality

Bivalves have been proven to be an inexpensive method for removing suspended solids, dissolved nutrients, and controlling algal growth through suspension feeding. The freshwater mussel, Elliptio complanata, is one of the most abundant species in Delaware, and it is additionally favorable for this experiment because of its hardiness against environmental stress and its filtration efficiency. This study examines the possibility that biomechanical filters such as E. complanata can supplement existing chemical and mechanical filtration regiments in aquaculture pond management. Twelve earthen aquaculture ponds located at the Delaware State University were stocked at a density of 4,000 catfish (Ictalurus punctatus) per hectare. Four different concentrations (0, 75, 150, and 300) of E. complanata were placed in trays within the ponds with three replicates of each concentration. The trays were suspended 15 cm below the surface of the water for a period of five months. Fish were fed a 32% protein diet twice daily at a rate of 1% of their body weight. Water quality was analyzed weekly while fish and mussel growths were measured biweekly. Results from water quality parameters varied significantly and were not conclusive based on the data obtained in this study. Water quality did not improve within the mussel treatment ponds during the course of this study and was found to be significantly below that of control ponds for all of the water chemistry parameters measured, with the exception of ammonia. Catfish in the 150 mussel treatment ponds grew the fastest; the 75 mussel treatment provided the most growth in mussels; and the 300 mussel group maintained the highest mussel survivorship. Although there were differences between ponds, fish growth and survivorship were not significantly different between treatments. While our mussel densities may have not been sufficient, their placement within the water column may have added additional stress. Being removed from the sediment can result in a decreased clearance rate in a benthic species such as E. complanata. This study may not have been conclusive in proving that mussels can be used to maintain water quality in aquaculture ponds, but we did see positive growth and survivorship of mussels and fish that indicated that the mussels were thriving in the aquaculture pond setting. This study may show that aquaculture ponds provide a suitable habitat in which propagated mussels may be held until their release into native areas.     

Differential effects of age-structured common carp (<Emphasis Type="Italic">Cyprinus carpio</Emphasis>) stocks on pond invertebrate communities: implications for recreational and wildlife use of farm ponds

Sustainable development of common carp Cyprinus carpio pond fisheries in Europe postulates their multifunctional use, integrating exploitation of aquaculture resources with recreational services and maintenance of high levels of local biodiversity. Age classes of farmed carp are grown separately and pond ecosystems may be differently affected by different ontogenetic stages of fish. To examine these relationships, a study was conducted on spring and summer diet of carp, invertebrate abundance and community structure, and water quality characteristics in ponds stocked with three carp age classes in SE Poland. With the exception of young-of-the-year fish in spring, benthic dipterans prevailed in the diets of all carp age classes and their consumption increased from spring to summer. Zooplankton featured in the diet of carp only in spring. Medium- and large-sized cladocerans predominated among microcrustaceans found in the guts of one- and two-year-old carp. Consequently, in summer, total biomass of medium- and large-sized cladoceran grazers was substantially lower in ponds stocked with older-age fish than in ponds used for production of 1-summer-old fingerlings. The relatively sparse submerged vegetation cover and low water transparency in ponds with older fish stocks compared to ponds with young-of-the-year carp indicate a transition to a turbid water state mediated by a trophic cascade mechanism in the presence of older-age fish. Densities of water-column macroinvertebrates decreased with the age of carp in the ponds. These results suggest that non-aquaculture use of carp ponds should be diversified according to their environmental quality. Fingerling rearing ponds are more suitable for environmentally friendly multifunctional use than ponds with older stocks.     

应用高通量测序技术分析拟穴青蟹肠道及其养殖环境菌群结构

采用基于Illumina Hi Seq测序平台的高通量测序技术,对拟穴青蟹(Scylla paramamosain)肠道及其养殖池塘水体、底泥中细菌种类及丰度进行了研究。测序结果显示,3个样品共获得有效序列234575条,可聚类于2812个分类操作单元(OTUs),归属于拟穴青蟹肠道、养殖水体、池塘底泥样品的操作分类单元(OTU)个数分别为453、706和2547,其中有184个OTU均能在3个样品中检测到,在青蟹肠道和养殖水体、青蟹肠道和池塘底泥中分别检测到197和309个共有OTU。物种注释结果显示,拟穴青蟹肠道中优势细菌种类为变形菌门(Proteobacteria)(39.96%)、柔膜菌门(Tenericutes)(23.09%)和厚壁菌门(Firmicutes)(16.58%);养殖水体中优势细菌种类为变形菌门(63.02%)、放线菌门(Actinobacteria)(24.96%)和拟杆菌门(Bacteroidetes)(8.41%);池塘底泥中优势细菌种类为变形菌门(75.23%)、拟杆菌门(5.72%)和放线菌门(3.83%)。此外,对各样品中丰度最高的前10位OTU分析显示,不同样品中占优势地位的10种细菌在数据库(SILVA)缺乏相关已知序列,并且各样品中的优势细菌种类完全不同。实验结果表明拟穴青蟹肠道与其池塘养殖环境中菌群结构存在着密切的相关性,但肠道菌群同时具有一定的独立性,其优势细菌种类与养殖环境中优势细菌种类无关。本研究旨在为拟穴青蟹健康养殖和微生态调控提供实验依据。     

Effects of introducing ducks into fish ponds on water quality, natural productivity and fish production together with the economic evaluation of the integrated and non-integrated systems

Raising ducks on fish ponds (fish-duck culture) on a commercial scale is a new practice in Egypt, therefore, a study was undertaken to evaluate this practice from production, carcass composition and economic viewpoints.Five earthern ponds were used in the non-integrated system (no ducks) whereas four earthen ponds, in which each pond was supplied with 125 Pecking ducks per 0.42 ha, were used for the Integrated system. In both systems, each pond was stocked with four species of fish (common carp Cyprinus carpio, silver carp Hypophthalmichthys molitrix, Grey mullet Mugil cephalus and tilapias Oreochromis niloticusand O. aureus) at the same densities.There were no differences in temperature or pH in any of the ponds but dissolved oxygen levels were lower in integrated ponds concomitant with increasing levels of ammonia, phosphate and nitrate. Water in integrated ponds was richer in natural productivity (phytoplankton and zooplankton) either in species or density when compared with those variables in non-integrated ponds.Fish species reared in integrated ponds exhibited better body weight, food conversion and protein efficiency ratios compared with those of fish species in the non-integrated ponds. Fish yield per 0.42 ha produced from the integrated ponds was significantly higher than that obtained from non-integrated ones. Also, body composition of fish species was affected by the type of farming. Carcass crude protein of grey mullet, silver carp and tilapia was improved in the integrated system. The data on return on sales, return on costs, return on equity, pay-back period and break-even point showed that the integrated system was more profitable than the non-integrated system.     

Limnology of Macrobrachium amazonicum grow‐out ponds subject to high inflow of nutrient‐rich water and different stocking and harvest management

We evaluated the water characteristics and particle sedimentation in Macrobrachium amazonicum (Heller 1862) grow‐out ponds supplied with a high inflow of nutrient‐rich water. Prawns were subject to different stocking and harvesting strategies: upper‐graded juveniles, lower‐graded juveniles, non‐graded juveniles+selective harvesting and traditional farming (non‐grading juveniles and total harvest only). Dissolved oxygen, afternoon N‐ammonia and N‐nitrate and soluble orthophosphate were lower in the ponds in comparison with inflow water through the rearing cycle. Ponds stocked with the upper population fraction of graded prawns showed higher turbidity, total suspended solids and total Kjeldahl nitrogen than the remaining treatments. An increase in the chemical oxygen demand:biochemical oxygen demand ratio from inlet (4.9) to pond (7.1–8.0) waters indicated a non‐readily biodegradable fraction enhancement in ponds. The sedimentation mean rate ranged from 0.08 to 0.16 mm day^?1 and sediment contained >80% of organic matter. The major factors affecting pond ecosystem dynamic were the organic load (due to primary production and feed addition) and bioturbation caused by stocking larger animals. Data suggest that M. amazonicum grow‐out in ponds subjected to a high inflow of nutrient‐rich water produce changes in the water properties, huge accumulation of organic sediment at the pond bottom and non‐readily biodegradable material in the water column. However, the water quality remains suitable for aquaculture purposes. Therefore, nutrient‐rich waters, when available, may represent a source of unpaid nutrients, which may be incorporated into economically valued biomass if managed properly.     

不同季节刺参养殖池塘沉积物菌群结构及其影响因素

本研究以辽宁省营口地区刺参(Apostichopus japonicus)养殖池塘为研究对象,利用高通量测序技术,构建不同季节刺参养殖池塘沉积物菌群16S rRNA基因测序文库,解析刺参养殖池塘沉积物菌群的季节性差异和共性,查明影响沉积物菌群构成的主导环境因子。结果显示,营口地区刺参养殖池塘沉积物菌群的丰度和多样性以夏季最高,春秋次之,冬季最低。不同季节刺参养殖池塘沉积物差异菌群呈显著性季节演替特征(P<0.05)。其中,春季差异菌群主要隶属于拟杆菌门(Bacteroides),夏季差异菌群主要隶属于酸杆菌门(Acidobacteria)、疣微菌门(Verrucomicrobia)和浮霉菌门(Planctomycetes),秋季差异菌群主要隶属于厚壁菌门(Firmicutes),冬季差异菌群主要隶属于放线菌门(Actinobacteria)。尽管不同季节沉积物细菌组分比例不同,但第一优势菌门均隶属于变形菌门(Proteobacteria)(相对丰度>43.19%)。环境因子中,影响刺参养殖池塘沉积物菌群的主导环境因子为温度、总有机碳、总氮和pH。本研究将为刺参养殖池塘微生态调控提供理论参考。     

Seasonal dynamics of fish assemblage in a pond canal

The annual dynamics of fish assemblage in a pond-connecting canal of a South Moravian pond aquaculture facility was studied to reveal potential assemblage effects on pond stocks and vice versa. The species richness of fish assemblage and seasonal dynamics of its development were predominantly dependent upon the fish stock of the interconnected ponds (particularly due to escapees during the period of pond harvesting), which contributed to a considerable increase of commercial fish species occurrence. Using a seasonal parameter, the season proved to have a major impact on fish assemblage dynamics (r = −0.71, P < 0.001). Spring samples were dominated by commercial fishes of aquaculture origin (mainly Cyprinus carpio). Occurrence of several fish species originating from the wild (bleak, Alburnus alburnus, chub, Leuciscus cephalus and roach, Rutilus rutilus) was also reported. The pond canal was found to be an important reservoir site of persistent survival and potential subsequent spreading of some undesirable alien fishes such as topmouth gudgeon (Pseudorasbora parva) and gibel carp (Carrasius auratus). Moreover, more attention should be paid to the potential negative impacts of all fishes of aquaculture origin upon the natural ecosystem and to the adverse effects due to the immigration of wild fish into aquaculture pond farming units.     

Bacterial communities in Chinese grass carp (Ctenopharyngodon idellus) farming ponds

Bacterial communities in the water column and sediment of 12 commercial grass carp (Ctenopharyngodon idellus) farming ponds were analysed. At the same time, physical and chemical environmental parameters were measured, including secchi depth (SD), total nitrogen (TN), total phosphorus (TP) and chemical oxygen demand (COD_Mn). From 12 water samples and 12 sediment samples, 39 different ribotypes were detected with PCR‐denaturing gradient gel electrophoresis (PCR‐DGGE). The ribotype richness showed that bacterial species in the water column differed among these ponds, and the result of sequencing further revealed the dominant and common bacterial species. In total, 32 bacterial species belonging to seven phyla (Proteobacteria, Bacteroidetes, Actinobacteria, Cyanobacteria, Acidobacteria, Fibrobacteres and Fusobacteria) were identified. Ordination via canonical correspondence analysis (CCA) on the DGGE data and environmental parameters indicated that the composition of bacterial community was significantly influenced by SD.     

Bacterial community of pond's water,sediment and in the guts of tilapia (Oreochromis niloticus) juveniles characterized by fluorescent in situ hybridization technique

Information about bacterial community structure and functioning in fish farming ponds remains scarce, mainly due to methodological difficulties in counting and identifying uncultured bacteria. The main objective of this study was to evaluate the degree of similarity between the bacterial community of the digestive tract of tilapia (Oreochromis niloticus) juveniles and that of the test pond's water and sediment, using the Fluorescent In Situ Hybridization (FISH) technique. Samples of water, sediment and gut content of 30 tilapia juveniles from a single nursery ground were collected in January 2010. Potentially probiotic and pathogenic bacteria of the species Bacillus, Lactobacillus brevis, Lactobacillus collinoides, Lactobacillus coryniformis, Lactobacillus farciminis, Vibrio and Pseudomonas fluorescens were found in different samples using specific fluorescent probes. The similarity between bacterial community environments and gastrointestinal tracts was determined using the Morisita‐Horn index. The fish guts presented higher abundances of Pseudomonas fluorescens, Bacillus, Lactobacillus brevis and Lactobacillus collinoides. The bacterial community composition of tilapia gastrointestinal tract was more similar to the water than the sediment of the pond. The results of this study showed that the FISH technique can be easily used for monitoring of probiotics and pathogen detection in aquaculture systems.     

The effect of four microbial products on production performance and water quality in integrated culture of freshwater pearl mussel and fishes

An 80‐day mesocosm experiment was conducted to evaluate the effect of four commercial microbial products on production performance and water quality in integrated culture of freshwater pearl mussel Hyriopsis cumingii, grass carp, gibel carp, silver carp and bighead carp. Five treatments were tested. One treatment with non‐supplementation of microbial products served as control (C). In the other four treatments, Novozymes Pond Protect (NO), Bio‐Form BZT‐Water Reform (WR), Bacillus natto (BN) and Effective Microbes (EM) were added at the intervals of two weeks, respectively. Mussel yield declined in the tanks with supplementation of the microbial products. No significant differences were found in fish yield and chemical water quality among the treatments except total nitrogen (TN) was higher in tanks EM than in tanks C. Biomass of phytoplankton and Cyanophyta was higher in tanks NO, WR, BN and EM than in tanks C. Supplementation of the microbial products resulted in change in bacterial community in which Actinobacteria, Chlorobi, Verrucomicrobia and Proteobacteria dominated. Bacterial community in the tanks was significantly affected by TN, total phosphorus, chemical oxygen demand and Cyanophyta biomass. This study reveals that the function of these microbial products as probiotics is limited in H. cumingii farming.     

Principal component analysis of interactions between fish species and the ecological conditions in fish ponds: II. Zooplankton*

Abstract. Interactions between fish species as to their effect on the zooplankton populations in the ponds were studied in ten ponds of 0–1 ha each. The ponds were stocked with bottom-feeding fish: common carp, Cyprinus carpio L., and male hybrid tilapia Oreochromis niloticus L. ×O. aureus (Steindachner), and a filter feeder: silver carp, Hypophthalmichtys molitrix (Valenciennes), at varying proportions. A Principal Component Analysis of the data showed that the fish combination present in the pond accounted for 30% of the overall variability, through the first two components. The first zooplanktonic component (ZC1) can be considered as expressing community structure, showing high zooplankton diversity on one pole and low diversity on the other. The second component (ZC2) is related to the time of appearance of certain zooplankton groups. The most striking differences occurred between ponds with and without silver carp. The presence of the other bottom-feeding fish caused a reduction of zooplankton diversity, but not so pronounced as that of silver carp. The interactions among silver carp, zooplanktonic trophic groups and algal size are discussed. It is concluded that the effect of silver carp on the zooplanktonic community is a compound one, which includes both direct predation and depletion of their food resources.     

Integration of duck and fish farming: Experimental results

In 1977 and 1978, two fish ponds at the Dor Aquaculture Experiment Station were integrated with duck production. Each pond's area was 400 m² and they were stocked with a polyculture of common carp, Tilapia, silver carp and grass carp (White Amur). The ducks were fed with prepared, nutritionally balanced feed, while the fish had to get by with the ducks' droppings plus the feed dropped directly from the ducks' beaks into the ponds. The ducks' performance on the ponds was superior to their ‘land’ control in growth rate, feed efficiency, viability and cleanness of feathers and skin. The average daily gain of the fish was 38.5 kg ha^?1, not significantly different from ponds receiving similar mixtures of dry poultry manure plus supplementary feeds.Our experimental results provide necessary empirical support to the conclusion that the system is very efficient and its use should be expanded in warm water aquaculture.     

Fish-management relationships in Israeli commercial fish farming

To analyse the relationships among fish species performance and management procedures, a database was built up with data from 31 fish farms during the period 1976–1987 (1673 observations) and analysed through multivariate statistics (factor analysis). The data include nurseries, grow-out and operational ponds with mono- and polycultures of common carp, Cyprinus carpio, tilapia hybrid, Oreochromis niloticus × O. aureus, silver carp, Hypophthalmichthys molitrix, and mullet, Mugil cephalus. The main conclusions include the following. (1) The highest total yields and best tilapia performances were obtained in polyculture ponds where tilapia was the main species. (2) The best carp performances occurred in grow-out polyculture ponds where carp was the main species. Carp performance was improved in polycultures with mullet and silver carp, irrespective of whether tilapia were present or not. (3) Carp and tilapia yields increased as the nutritional inputs (feed pellets, sorghum pellets, manure), pond size and culture duration increased. The effect of the nutritional input was not linear, but logarithmic. (4) Growth rate of common carp was more affected by total density and stocking size than that of tilapia. Better carp and tilapia growth occurred in grow-out ponds when stocked at large sizes and cultured during short periods, mainly when both species were present. (5) Carp growth varied with the geographical region and size of fish pond, being better in smaller than in larger ponds due to reduced access to natural benthic food in deep ponds.     

鱼蚌混养对池塘水质、藻相结构及三角帆蚌生长的影响

2012年4月26日—2012年12月12日通过在鲢鳙鱼养殖池塘中放养不同密度的三角帆蚌,研究不同三角帆蚌放养比例对鲢鳙鱼养殖池塘中水质、藻相结构及三角帆蚌生长的影响。实验中,鲢鳙放养比例统一为3∶7,总密度为1.5尾/m3。三角帆蚌放养密度则设置4个水平,分别为单养鲢鳙鱼池塘(0只/m3),低密度三角帆蚌混养池塘(0.8只/m3),中密度三角帆蚌混养池塘(1.0只/m3)和高密度三角帆蚌混养池塘(1.2只/m3)。结果显示,混养三角帆蚌池塘的水化指标(TP、PO4-P、NH3-N、NO2-N和NO3-N)均显著低于单养鱼池塘。中密度三角帆蚌混养池塘除NH3-N和化学需氧量(COD)与低密度三角帆蚌混养池塘无显著差异外,其他各项水化指标均显著低于其他3个池塘,并且极显著低于单养鲢鳙鱼池塘。单养鲢鳙鱼池塘藻类平均密度均极显著高于鱼蚌混养池塘,其中在鱼蚌混养池塘中浮游植物密度与三角帆蚌密度成负相关关系。单养鲢鳙鱼池塘的浮游植物生物量均极显著低于中、高密度鱼蚌混养池塘,并且显著低于低密度混养池塘。浮游植物生物量与三角帆蚌密度成正相关关系,鱼蚌池塘中绿藻和裸藻的生物量在养殖过程中上升显著。低、中密度三角帆蚌混养池塘三角帆蚌存活率均显著高于高密度三角帆蚌混养池塘;低密度混养池塘中蚌湿重、壳长及壳宽相对增长率均为最大,显著高于中、高密度三角帆蚌混养池塘。研究表明,养鱼池塘混养三角帆蚌不仅能改善养殖池塘的水质,还能控制藻类数量,促使绿藻和裸藻等大型藻类的生长,提高养殖水体浮游植物的生物量总量,最终还能有效提高三角帆蚌的存活率及生长率。从改善水质,藻相结构,蚌成活率及生长等指标角度考虑,在鲢鳙鱼养殖池塘中,三角帆蚌最佳放养密度为1.0只/m3。     

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.     

Comparison of bacterial communities in channel catfish Ictalurus punctatus culture ponds of an industrial ecological purification recirculating aquaculture system

The industrial aquaculture pond system has gradually replaced the use of traditional earthen pond, as it causes less pollution and is more economical. In this study, an industrial ecological purification recirculating aquaculture system consisting of the water source pond, high‐density culture ponds, a deposit pond, and ecological purification ponds for channel catfish cultivation was established. Twelve water samples from different ponds were sequenced, and the bacterial communities were analysed. The abundances of Cyanobacteria and Merismopedia varied in different functional ponds of the system. The water quality was stable after two months of cultivation at 1.89 ± 0.22 mg/L total nitrogen, 1.1 ± 0.08 mg/L NH₄‐N and 0.43 ± 0.1 mg/L total phosphorus. The fish weight increased in a nearly linear manner, reaching 237.63 ± 23.8 per fish at day 120. An analysis of the environmental parameters, water quality and fish weight suggested that the system had an effective water purification process. Canonical correspondence analysis showed that the community was affected at the genus and phylum levels by different environmental parameters. We identified several dominant beneficial bacteria with nutrient removal abilities. Overall, our results demonstrated that the ecological purification recirculating aquaculture system had notable effects on water quality improvement and promoted changes in bacterial populations. These results provide important information on the microbial ecology of pond industrial eco‐aquaculture systems.