Fish Polyculture Research Articles

Does bivalve mollusc polyculture reduce marine fin fish farming environmental impact?

The ability of bivalve culture in the proximity of an open water fin fish farm to reduce the environmental impact caused by organic wastes was tested. The experiment involved floating net cages containing cultured gilthead sea bream ( Sparus aurata) and European sea bass ( Dicentrarchus labrax) in the western Mediterranean. Two bivalve species, oyster ( Ostrea edulis) and mussel ( Mytilus galloprovincialis), were deployed for 3 months along a distance transect running from 0 to 1800 m from the fish cages. Shell growth, flesh dry weight, the concentration of stable isotopes of carbon and nitrogen, and metal accumulation (Cd, Pb, Cu and Zn) in the bivalves were analyzed. Bivalves showed significant growth compared with their respective starting sizes, although closeness to the fish farm did not enhance such growth. The stable isotopes content indicated that there was no relationship between the main input of organic matter from the fish farm (the feed) and the trophic behavior of the bivalves. Neither did metal accumulation show a trend along the distance gradient from the fish farm. All the results were consistent in indicating that neither oysters nor mussels fed on fin fish farming wastes. This work demonstrates that the polyculture of fin fish and bivalves does not represent an appropriate tool for reducing the environmental impact of fin fish aquaculture in open water.

Economic evaluation of three on-station fish farming technologies

The economic viability of three aquaculture research technologies was examined to determine the operational profitability in Ghana. The first technology was aimed at producing improved tilapia strain fish seed as input for fish farming, while the second dealt with integrating poultry with fish farming for harnessing synergies of waste recycling and feeding cost reduction. The third technology involved polyculture of fish utilizing the natu-ral feed available to different trophic types of fish within a communal culture environment. While the technolo-gies were considered to be socially desirable that could ensure efficiency in use of resources, screening on-station was germane in technology transfer. Undiscounted profit, rate of return, return on annual operation cost, benefit-cost ratio, return to management, and land were adopted as indicators for assessing viability of the tech-nologies and approaches that could improve profitability. At rate of return of 29.8 %, return on annual operation cost of 43.9 %, benefit-cost ratio of 1.7 and return to management and land of 71.2 %, the communal culture technology involving tilapia-mullet-prawn-catfish gave positive indicator values, but the risk of survival of the species in the culture medium must be minimized. Sensitivity analyses of making gains at the same levels of costs for the other two technologies showed that an eight-fold increase of revenue would be required for the poultry-fish integration model to be viable, while a three-fold increase of revenue would be required for the via-bility of fish seed production. Since the three technologies address different challenges of fish farming, all could be recommended for implementation, with the proviso of maximizing incomes from sales of produce, reducing costs of inputs, and minimizing risks.

Economics of fish farming in Ibadan Metropolis

The study assesses the economics of fish farming in Ibadan Metropolis. The data for the study were collected from 50 fish farmers with the aid of structured questionnaires. The data were analyses using descriptive, gross margin and regression techniques. The study revealed that most farmers had secondary education and above. Most farmers operate at small-scale level with an average of 3 ponds in this category. Fish farmers practiced poly culture fish farming. Clarias spp is the most raised fish species followed by Heteroclaria spp. The gross margin analysis revealed that medium scale farmers derived the highest return of 1.55 for every one naira expended. This is followed by large scale farmers at l.52 for every one naira compared with only 1.34 for every naira spent by small-scale farmers. Fixed inputs, labour, fertilizers, feeds and finger lings significantly affect the value of fish produced. Fish farmers under utilize both labour and fertilizers while feeds and finger lings are over utilized. Key words: Aquaculture, fish production, Profitability and efficiency

Introduction of jundia Rhamdia quelen (Quoy & Gaimard) and Nile tilapia Oreochromis niloticus (Linnaeus) increases the productivity of carp polyculture in southern Brazil

Fish polyculture is based on the assumption that each species has its own feeding niche and may increase the maximum standing crop of a pond by exploring a wider range of available food and ecological niches. In order to identify the better species ratio and to introduce jundia (JN) (Rhamdia quelen Quoy & Gaimard) and Nile tilapia (NT) (Oreochromis niloticus Linnaeus) in to the carp polyculture practiced in South Brazil, a 162-day experiment was conducted, in 12 250-m2 earthen ponds (1.2 m deep). Treatment I (T-I) contained 35% common carp, Cyprinus carpio (L.) (CC); 35% grass carp, Ctenopharyngodon idella Valenciennes (GC); 15% silver carp, Hypophthalmichthys molitrix Valenciennes (SC); and 15% bighead carp, Aristichthys nobilis Richardson (BC). Treatment II (T-II) consisted of three ponds stocked at the following ratio: 17.5% CC, 35% GC, 15% SC, 15% BC and 17.5% JN. Treatment III (T-III) consisted of three ponds with 35% CC, 35% GC, 7.5% SC, 7.5% BC and 15% NT. Treatment IV (T-IV) consisted of three ponds with 17.5% CC, 35% GC, 7.5% SC, 7.5% BC%, 17.5% JN and 15% NT. No significant correlation was found between the treatments with different species ratio and water quality parameters. The final weight of different species, in different treatments, was statistically different. The major result was the clear positive effect on growth parameters observed by the introduction of JN and/or NT in to the carp polyculture. The yield per hectare was 2083.33±183 kg ha−1 for polyculture with carp species; 2476.67±139.88 kg ha−1 following the introduction of JN only; 2801.67±111.42 kg ha−1 for isolated introduction of NT; and 2506.67±422.31 kg ha−1 for simultaneous introduction of JN and NT. The introduction of JN and/or NT had a positive effect on growth parameters when compared with carp-only polyculture. The reduction in CC ratio also had a positive effect on growth parameters.

Modelling of energy transformations in fertilized tropical fish ponds

AbstractThe energy budget patterns of three tropical ecosystems in which the polyculture of fish was practised were studied. The rates of organic production of the three tropical ponds over two annual cycles were evaluated. Study of the utilization of energy in the three ponds, which were fertilized with vermicompost, cow dung and diammonium phosphate, revealed that herbivores were more efficient in utilizing energy than were autotrophs. The available energy in these systems was supplied by autochthonous sources. Silver carp was found to be the most efficient organism in converting energy in the grazer food chain in the ponds. The efficiency of the system in regard to fish production was 0.052, 0.049, and 0.051%, respectively, of the total available solar radiation. Organisms in various trophic levels were all characterized by energy changes in the studied ponds, forming the food webs contained in them.

C, N and P regeneration by a detritivorous fish, Liza haematocheila T. & S.: effects of temperature, diet and body size

Detritus, as a nutrients reservoir, affects the trophic structure and dynamics of communities and supports a greater diversity of species and longer food chains. Detritivorous fish is an important organism to regenerate the nutrients from sediments. Despite the numerous studies on the nutrients cycle in fish, only a few attempts have been made to quantify the regenerating ability. In the present study, we chose the common detritivorous fish redeye mullet as the research object. Redeye mullet is also a common poly-culture fish in China. Diet, including a commercial diet mostly used in aquaculture and a home-made diet with contents close to detritus, was used and considered as a fixed factor. Temperature was also considered as a fixed factor as much research has shown that temperature has significant effects on fish metabolism. Moreover, body size was regarded as a covariate under analysis of covariance. Three key nutrients, namely carbon, nitrogen and phosphorus, were used to measure the nutrient-regenerating ability of redeye mullet under laboratory conditions. The results showed that the nutrient regeneration in percent of the consumption decreased with increasing temperature. Carbon and nitrogen regeneration of redeye mullet fed on commercial diet was lower than those of the home-made diet group, while the opposite was found for phosphorus. In each group, the amount of regenerated nutrients increased linearly with body size. Fed on the home-made diet, 5-g fish at 25 degrees C can regenerate 210.822 mg C, 37.533 mg N and 0.727 mg P per day.

Effects of silver carp and the small indigenous fish mola Amblypharyngodon mola and punti Puntius sophore on fish polyculture production

A sustainable semi-intensive pond aquaculture technology including major carp species as cash-crop and small indigenous fish species (SIS) as food for the farmers' families is being optimized in Bangladesh. The inclusion of silver carp (Hypophthalmichthys molitrix), a cheap large species affordable by poor farmers, is now being considered. As part of a study on the effects of this filter feeder on polycultures including the large carps rohu (Labeo rohita), catla (Catla catla) and common carp (Cyprinus carpio) and the SIS punti (Puntius sophore) and mola (Amblypharyngodon mola), an experiment was carried out under farm conditions to test the effects of silver carp and of each SIS species on the growth, survival and yield of the large and small species and on pond ecology.The experiment was performed in 38 farmers' fishponds of different sizes, from 220 m2 to 1200 m2. The results show that the larger the fish pond the better rohu performance, the larger punti fry weight and the lower punti fry harvested biomass. Pond size did not affect other fish species. The addition of 250 mola and/or punti per 100 m2 fishponds affected rohu and catla and did not affect common and silver carps. The addition of mola alone reduced rohu's parameters by 15%. The addition of SIS in the three combinations tested (250 mola, 250 punti, 125 of each species) reduced catla's parameters by 20–24%. Punti fry were larger when both SIS were stocked and punti fry biomass was larger when only punti were present. Total mola harvested biomass and yield were larger when the entire SIS stocked were only mola.The addition of 10 silver carp over the 99 large carps stocked per 100 m2 fishponds negatively affected rohu and catla growth and yield by about 15–21% and 45–50% respectively but not their survival, did not affect common carp performance, did not affect punti and mola reproduction in the ponds, reduced punti yields by 25%, reduced mola performance by about 35%, and silver carp own biomass increased total yield and total income in about 12% each. These effects are explained and discussed considering fish interactions through the food web. The decreased income from selling the more expensive large carps is more than compensated by that obtained from silver carp, which allows the option to the farmer to sell part of the silver carp to complete the cash income that would have been obtained from large carps only if silver carp would not be stocked, and consume the rest with the family.

Stable isotope and fatty acid evidence for uptake of organic waste by green-lipped mussels Perna viridis in a polyculture fish farm system

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 317:273-283 (2006) - doi:10.3354/meps317273 Stable isotope and fatty acid evidence for uptake of organic waste by green-lipped mussels Perna viridis in a polyculture fish farm system Qin-Feng Gao1, Paul K. S. Shin1,2, Guang-Hui Lin3,4, Shi-Ping Chen3, Siu Gin Cheung1,* 1Department of Biology and Chemistry, and 2Centre for Coastal Pollution and Conservation, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong SAR, China 3Laboratory of Quantitative Vegetation Ecology, Institute of Botany, the Chinese Academy of Sciences, Beijing 100093, China 4Department of Global Ecology, Carnegie Institution of Washington, 260 Panama Street, Stanford, California 94305, USA *Corresponding author. Email: bhsgche@cityu.edu.hk ABSTRACT: To evaluate the feasibility and capability of using filter-feeding bivalves as biofilters for organic waste derived from fish faeces and feed wastage in marine fish culture activities, a polyculture system comprising fish and green-lipped mussels Perna viridis was developed by transplantation of mussels into fish cages. As a control, mussels from the same population were simultaneously transplanted to a distant reference site free of effects from fish farming activities. After 3 mo acclimation, samples of mussel tissue, particulate organic matter (POM), fish feed and fish faeces were collected for measurements of carbon and nitrogen isotopic ratios and fatty acid profiles. Enrichment of 13C and 15N in mussel tissue collected inside the fish cages as compared to those at the reference site indicated the uptake and assimilation of isotopically heavier fish feed and fish faeces. Compared with mussels from the reference site, the pattern of fatty acid profiles and single fatty acids of mussels in fish cages also tended to be closer to fatty acid profiles of fish feed from fish farms. Based on the concentration-weighted isotope mixing model, the proportions of mussel biomass assimilated from POM, fish feed and fish faeces to mussel dietary consumption were 68.3, 27.5 and 4.2%, respectively. The direct uptake of organic waste from fish farms by filter-feeding mussels is different to their consumption of phytoplanktonic biomass, because the nutrient flux is shifted between these 2 distinct pathways. KEY WORDS: Fish farming · Stable isotopes · Fatty acid profiles · Perna viridis · Biofiltration Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 317. Online publication date: July 18, 2006 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2006 Inter-Research.

Alternative species for traditional carp polyculture in southern South America: Initial growing period

Fish polyculture is practiced aiming to increase productivity. Complementary species can increase the maximum standing crop of a pond by allowing a wider range of available foods and ecological niches. The present work was conducted in an attempt to identify the better species ratio and the introduction of jundia ( Rhamdia quelen) and Nile tilapia ( Oreochromis niloticus) in the traditional fish polyculture practiced in South Brazil. The experiment was conducted over 86 days, in nine 250 m 2 earthen ponds (1.2 m deep), and comprised the initial growing period of fish. As control, one pond was stocked with a species ratio usually employed in the region: 35% common carp, Cyprinus carpio (CC), 35% grass carp, Ctenopharyngodon idella (GC), 15% silver carp, Hypophtalmichthys molitrix (SC) and 15% bighead carp, Aristichthys nobilis (BC) with a density of 2875 fish/ha. Treatment I consisted of two ponds stocked with the same species ratio, but with a density of 5750 fish/ha; this fish density was also used in the remaining treatments. Treatment II consisted of two ponds with 20% CC, 30% GC, 10% SC, 20% BC and 20% jundia (JN). Treatment III consisted of two ponds with 35% GC, 5% SC, 10% BC, 20% JN and 30% Nile tilapia (NT). Treatment IV consisted of two ponds with 15% CC, 30% GC, 5% SC, 10% BC, 20% JN and 20% NT. All water quality parameters evaluated were within acceptable limits for fish culture in pond water. No significant correlation was found between species rate and the water quality parameters. The final weight of different species, in different treatments, showed statistical differences. Considering growth parameters, the best result was obtained in treatment IV. A complete exclusion of the CC in treatment III had no advantage over the other treatments; however, the reduction of CC percentage from 35% to 15% allowed the introduction of JN, with positive effects. In addition, the introduction of JN in the polycultures tested had no effect over the other species. Nile tilapia grew better in treatment III with no CC, but CC had a better performance in the presence of NT. Based on the data presented herein, the most promising polyculture ratio for initial growing season seems to be that used in treatment IV. The reduction of the CC ratio and the introduction of NT and JN had positive effects in all growth parameters evaluated.

The Impact of Nutrient Concentration (N:P) and Manure Type on Fish Polyculture

Nutrient availability is considered to have a major role in controlling primary productivity. Therefore, an important aspect of successful aquaculture management in fish culture systems is making available basic nutrients, for example, phosphorous (P), nitrogen (N), and carbon (C) in optimal concentrations. The use of fertilizers in relation to pond productivity has been studied in order to develop better fertilization procedures under given environmental conditions. Many researchers from across the world have suggested different N:P ratios for optimizing fish production. The primary aim of this study was to understand the influence of nutrient quality and quantity on fish and primary productivity in terms of optimizing fish production. Two objectives of this study include evaluating the performance of pig and cow manures in terms of primary productivity and fish production; and understanding the influence of different N concentrations ranging from 1-2 ppm on fish production while P was maintained at 0.5 ppm. It was evident from this research that fish species nutrient-sensitivity to nitrogen concentrations ranging from 1-2 ppm was significantly different. The 1 ppm N:0.5 ppm P concentration was found to be the most suitable nutrient ratio for pond fertilization as significantly higher fish production and lower mortality were recorded in this treatment. In terms of plankton and fish production, pig manure was found to be significantly more effective than cow manure. Higher nutrient (>1 ppm N) concentrations negatively impacted zoo-plankton and zoo benthos development. Daily manure application would considerably reduce the organic load in the fish culture system, enabling more efficient use of nutrients for primary and secondary production.

Effects of increasing the stocking density of large carps by 20% on 'cash' carp-small fish polyculture of Bangladesh

This experiment was carried out in the framework of a project to develop a viable fish polyculture technology under Bangladeshi conditions that allows simultaneous fish production of small indigenous species for the farmers' family consumption and of large carp species as a cash crop. The objectives of this experiment were to assess the effects on fish performance and on the environment of adding 20% large fish to the basic ‘cash crop’ carp–small fish polyculture consisting of 10 000 fish ha−1 of the large carp rohu Labeo rohita (Hamilton), catla Catla catla (Hamilton) and common carp Cyprinus carpio (L.) at a species ratio 1:1:1, and 15 000 fish ha−1 of each small indigenous fish punti Puntius sophore (Hamilton) and mola Amblypharyngodon mola (Hamilton) (control). The treatment ponds were stocked with additional 2000 large fish ha−1, either all rohu, or all catla, or all common carp, or half rohu and half common carp, or half catla and half common carp. The results obtained and the analysis of interactions through the food web that affect food resource availability of the different fish species and account for the trends and differences observed among treatments confirm the positive effect of common carp on rohu reported in previous experiments and show that a 20% increase in large carps stocking neither affect the survival of the large carps nor reduce harvesting biomass of the small fish for the farmer's family consumption. Increased stocking densities of each large carp species did not significantly reduce its own harvesting weight and mean growth rate, while significantly increased rohu and catla (but not common carp) harvesting biomass and yield. The complex relations between species led to inter- and intraspecific competition, which in some treatments increased growth or yield of one species and in other treatments of other species, so that the gains on one species and the losses on the other led to no significant total harvested biomass differences between treatments. Yet, the results herein reported may help farmers to select their species stocking ratios. Thus, if the main target of the farmer is rohu, then a stocking density increase of 10% common carp and 10% rohu would improve rohu growth rate (due to common carp) and result in 50% higher rohu harvesting biomass and yield. If the main target of the farmer is catla, then a 20% increase in catla stocking density would lead to 20% higher catla harvesting biomass.

Effects of adding different proportions of the small fish punti (Puntius sophore) and mola (Amblypharyngodon mola) to a polyculture of large carp

This experiment was carried out in the framework of a project to develop a viable fish polyculture technology under Bangladeshi conditions that allows simultaneous fish production of small indigenous species for the farmers' family consumption and of large carp species as a cash crop. The objectives of this experiment were to assess the effects of adding punti and mola in different proportions on the large carp and on the environment, and to assess the effects of punti on mola and mola on punti. The polyculture included the large carp rohu, catla and common carp (as cash crop fish), and the small indigenous fish punti and mola (as food for the small-scale farmer family). The total large carp stocking density was 10 000 fish ha−1, at a species ratio of 1:1:1. The total small fish stocking densities were 0 in the control and 30 000 punti and mola ha−1 in the treatments, these at rates 2:1, 1:1 and 1:2. Stocking punti and mola at the density and all ratios tested were viable solutions to obtain simultaneously large carp cash crops and small fish to feed the farmer's family. Statistically marginal differences in large carp production were obtained in stocking small fish in the different proportions. These marginal differences could be explained by food competition between punti and common carp and between mola and rohu, which had different outcomes depending on the proportions of the small fish stocked. Stocking punti and mola at a 1:1 ratio would result in more small fish for the farmer's family, while the individual size of rohu, the most expensive large carp, would be somewhat smaller, but not necessarily small enough to decrease its selling price. Stocking one of the small fish in higher proportion than the other (2:1 or 1:2) would result in less mola for the family consumption, while harvesting of common carp would be somewhat lower and of smaller fish. Since common carp is the cheapest of the large carps, this small reduction would not necessarily affect the family income in an important way. With these results, farmers would now be able to reorganize their stocking practices with large carps and small fish and decide the appropriate small fish stocking ratios to meet their needs.

Profitability and technical efficiency of aquaculture systems in pampaanga, philippines

We evaluate the profitability and technical efficiency of aquaculture in the Philippines. Farm‐level data are used to compare two production systems corresponding to the intensive monoculture of tilapia in freshwater ponds and the extensive polyculture of shrimps and fish in brackish water ponds. Both activities are very lucrative, with brackish water aquaculture achieving the higher level of profit per farm. Stochastic frontier production functions reveal that technical efficiency is low in brackish water aquaculture, with a mean of 53%, explained primarily by the operator's experience and by the frequency of his visits to the farm. In freshwater aquaculture, the farms achieve a mean efficiency level of 83%. The results suggest that the provision of extension services to brackish water fish farms might be a cost‐effective way of increasing production and productivity in that sector. By contrast, technological change will have to be the driving force of future productivity growth in freshwater aquaculture.

Effects of adding the small fish punti (Puntius sophore Hamilton) and/or mola (Amblypharyngodon mola Hamilton) to a polyculture of large carp

Abstract This experiment was carried out in the framework of a project to develop a viable fish polyculture technology under Bangladeshi conditions that allows simultaneous fish production of small indigenous species for farm families' consumption and of large carp species as a cash crop. The polyculture included the large carp rohu, catla and mirror carp as cash crop fish, and the small indigenous fish punti and mola as food for the small-scale household. Total large carp stocking density was 10 000 fish ha−1, at a species ratio 1:1:1. Total small fish stocking densities were 0, 25 000 or 50 000 fish ha−1. The objectives were to assess the effects of adding 25 000 punti and/or mola ha−1 on the large carp and environment, and to assess the effects of punti on mola and mola on punti. It was found that catla was not affected by the addition of small fish in any of the combinations tested; rohu was not affected by punti, and mola reduced rohu performance by 30–40% only when punti was not present; mirror carp was not affected by punti, and mola increased mirror carp growth rate and harvesting weight by 25–30% whether punti was present or not; small fish did not significantly affect total yield and food conversion ratio; punti performance was not affected by mola; mola harvesting weight was not affected by punti, while mola harvesting numbers and biomass were reduced by 55–65% by punti. Factor analysis of water quality data identified photosynthesis–respiration and algal biomass– temperature as the main processes governing water quality. Effects of treatment on those water quality factors are analysed, and the fish–water quality relationships discussed. In a parallel polyculture experiment in 25 farm ponds, the performance of large carp species was found to be unaffected by the addition of punti and/or mola. The results indicate that, at the densities tested, punti and mola addition to the large carp polyculture is viable as they do not reduce cash crop production and might be a good food source for the farmer's family.

The effect of rice-seeding rate and fish stocking on the floodwater ecology of the trench of a concurrent, direct-seeded rice-fish system

Concurrent rice-fish systems in the Mekong Delta, Vietnam, are characterized by a rice field surrounded by a trench (on average 1000 m2, covering 15–20% of the field surface). Rice is direct seeded and fish are reared in polyculture. The most common species for polyculture are silver barb Barbodes gonionotus (Bleeker), common carp Cyprinus carpio L. and Nile tilapia Oreochromis niloticus (L.). In a 1996–1997 dry season experiment, the effects of (1) absence or presence of a fish polyculture, and (2) two different rice-seeding rates (100 and 300 kg pre-germinated rice per ha) on the trench floodwater ecology were studied. Fish were stocked in six out of twelve rice-fish plots at the Co Do experimental rice-fish station (10° 10′ N and 105° 20′ E). Silver barb, common carp and Nile tilapia were stocked in polyculture at densities of 3150, 310 and 550 fish/ha, respectively. Several hydrological and biological parameters of the trench floodwater were measured. About 65% of the observed variation in the trench floodwater could be attributed to the fishes stocked and changes in rice-seeding rate. The presence of a fish polyculture increased the water turbidity of the trench floodwater, mainly through suspension of mineral and organic material through fish perturbation. At the lower rice-seeding rate, this resulted in a lower primary production. Photosynthetic activity, dissolved oxygen am and pm showed significant decreases, but only at the lower rice-seeding rate in the presence of fish. Fish polyculture presence resulted in lower ortho-phosphate concentrations, higher phytoplankton communities and higher Protozoa numbers, most probably due to a higher availability of nutrients through fish defecation and perturbation. The rice-seeding rate had a significant impact on pH am, pH pm and temperature pm readings. The survival rate for Nile tilapia and the gross production for Nile tilapia and common carp was higher at the lower rice seeding rate, most probably due to a better aquatic environment of the field. In terms of fish production, the trench floodwater environment was better than the field floodwater. The trench is a very important part of the rice-fish system. It serves as a refuge and supplies reasonable amounts of phytoplankton and zooplankton to the fish.

Reclamation of Wastewater for Polyculture of Freshwater Fish: Bioassays Using Chlorella and Gambusia

The feasibility of using the secondary effluents from two sewage treatment plants in Hong Kong (Yuen Long and Shek Wu Hui) for fish culture was assessed. Total ammonia contents in the two sewage effluents surpassed the level of 2 mg L(-1) recommended for wastewater fish culture. The two sewage effluents both needed essential elements for supporting algal Chlorella vulgaris growth, whereas only sewage effluent from Yuen Long had contaminants at toxic levels. Total ammonia in water explained more than 80% variations of toxicity of water samples to Gambusia patruelis, mosquito fish, according to regression analysis. Removal of ammonia from the sewage effluent is necessary before being used for fish culture. In addition, the rather high levels of heavy metals (Cu, Zn, Cd) in the effluent should be closely monitored.

Commercial Vegetable and Polyculture Fish Production in Bangladesh: Their Impacts on Household Income and Dietary Quality

Given the low access that women in rural Bangladesh have to productive assets, their crucial role as caretakers, and their high vulnerability to micronutrient deficiencies, numerous non-governmental organizations target women for food-based income-generating activities. Three such programmes were examined, which promote adoption of polyculture fish production (two sites) and commercial vegetable production (one site). The programmes evaluated had income generation—and not better nutrition—as their primary objective. The fish and vegetable technologies were found to be more profitable than rice production, although rice production provided a higher share of total income. On the basis of the evidence collected, there is little reason to believe that adoption of the two technologies has improved the micronutrient status of members of adopting households through better dietary quality. There was no finding of disproportionately high own-consumption of fish and vegetables by adopting households. The impacts on overall household income, although positive, were not strong. The effects of adoption on women's status and time allocation do not change this conclusion. It is consumers in general who benefit from research, extension, and credit programmes to increase the market supply of vegetables and fish. All other things being equal, increased market supply will lower prices for these foods. Although inflation-adjusted cereal prices in Bangladesh have fallen by 40% over the last 25 years (a remarkable achievement), real prices of lentils, vegetables, and animal products have increased by 25% to 50%. Real fish prices have perhaps doubled. Dietary quality for the poor may be declining over time due to these price effects.

Economic efficiency and optimum stocking densities in fish polyculture: an application of data envelopment analysis (DEA) to Chinese fish farms

Polyculture is commonly practiced in pond aquaculture where several fish species are reared together, creating a multi-output production structure. This study applied a nonparametric data envelopment analysis (DEA) technique for multiple outputs to: (1) measure economic or `revenue' efficiency and its technical and allocative components for a sample of Chinese polyculture fish farms; and (2) derive the optimum stocking densities for different fish species. The mean economic efficiency was estimated to be 0.74. Technical inefficiencies accounted for most of the production inefficiencies in Chinese fish farms. On average, farmers should increase grass carp and decrease black carp stocking rates. Smaller farms and those from the developed regions were found to be relatively more technically and economically efficient.

Sorting fish by computer vision

Abstract In fresh-water fish farms which grow a few fish species together in a pond (polyculture fish farming), it is necessary to sort harvested fish according to species and size for optimal marketing. An image processing algorithm for discrimination between images of three fish species had been developed and tested. It was based on the method of moment-invariants (MI) coupled with geometrical considerations and was therefore insensitive to fish size, two-dimensional orientation and location in the camera’s field of view. The algorithm was applied to images of carp ( Cyprinus carpio ), St. Peter's fish ( Oreochromis sp. ) and grey mullet ( Mugil cephalus ), grabbed by a CCD camera under different lighting conditions in a lighting chamber. Three separate imaging sessions were conducted: (1) 96 images of 16 fish were acquired while they were placed individually in the illumination chamber at six different positions; (2) 140 images of 35 fish at four different positions each; (3) 146 images of 73 fish at two different orientations each. The three sessions were conducted under different lighting conditions and the fish were received from different farms. Based on the MI of their whole body, fish species identification reached 100, 94 and 86%, respectively, for grey mullet, carp and St. Peter’s fish for the first set of images and 98, 96, and 100%, respectively, for the second set. Using the shape of the whole body to identify grey mullet and the shape of the tail to differentiate between carp and St. Peter's fish, 100, 89 and 92% correct classification was achieved, respectively. Fish mass can be closely estimated from their image area. The correlation coefficients between the mass and image area of grey mullet, carp and St. Peter’s fish were 0.954, 0.986, 0.986, respectively. Manually measured fish length also correlated well with fish length when calculated from their binary image (correlation coefficients of 0.950, 0.997 and 0.983 for grey mullet, carp and St. Peter’s fish, respectively).

Reclamation of wastewater for polyculture of freshwater fish: bioaccumulation of trace metals in fish

The main objective of the present study is to investigate the bioaccumulation of trace metals (Zn, Cu, Cd, Cr, Pb, Ni) in the polycultured fish. A series of eight ponds (Au Tau pond system) were constructed at Au Tau Fisheries Office, Hong Kong Agriculture and Fisheries Department. Polluted river water was pre-treated in the first four ponds by providing sedimentation (S1, S2) and aeration (A1, A2), the effluent from A2 was introduced into the remaining four ponds (C1–C4) for fish culture. Fries of six species of freshwater fish including silver carp, big head, grass carp, tilapia, common carp and black bass were stocked in the ponds (C1–C4) during 11/93–2/94 and 1/4 of normal fish food (peanut cake) was used in the fish ponds. Bimonthly sampling of fish was conducted from 3/94–1/95 and trace metal concentrations in fish flesh and viscera were examined. In addition, the distribution of trace metals in different components of the fish pond ecosystem was also investigated.The results showed that bioaccumulation of trace metals occurred in the organisms at the lower levels of the foodweb and no biomagnification was detected at the upper levels, except for Cu concentrations in mosquito fish. The results revealed that metals in viscera were allometric, negatively correlating with body length (p<0.05) (excluding Zn in the viscera of common carp), which suggested that metal metabolism in fish played an important role in metal accumulation in fish viscera. Comparisons of trace metal concentrations in the viscera of the fish were therefore conducted by Student's t-test with body size as the covariant and the results suggested that higher metal contents in the food led to higher metal accumulation in the viscera. Zn accumulation in common carp was different from that in other species, with the highest Zn accumulation in viscera and in flesh. More than 60% of variations of Zn concentrations in fish flesh could be explained by Zn concentrations in fish viscera and fish body length according to the regression analysis (p<0.001) (common carp excluded) but no such relationships were detected for other metals (Cu, Cd, Cr). Significantly higher concentrations of trace metals were obtained in the viscera of the polycultured fish than those in the flesh, which suggested that viscera played an important role in storing trace metals in fish. When compared with trace metal contents reported in other studies, the present study demonstrated similar values and the fish (flesh) cultivated in the treated wastewater seemed to be safe for human consumption, in terms of trace metal concentrations.