The budget of nitrogen in the grow‐out of the Amazon river prawn (Macrobrachium amazonicum Heller) and tambaqui (Colossoma macropomum Cuvier) farmed in monoculture and in integrated multitrophic aquaculture systems

This work determined the nitrogen inputs, outputs and accumulation in compartments of stagnant earthen ponds for the monoculture and integrated multi‐trophic aquaculture (IMTA) of the Amazon river prawn (Macrobrachium amazonicum) and tambaqui (Colossoma macropomum), using recycled hypereutrophic water. A completely randomized experiment was designed with four treatments and three replications: PM–monoculture with 30 prawns/m², FM ‐ monoculture with 3 fish/m², IMTA ‐ polyculture with 30 prawns/m² and 30 fish/m² free, POLY‐CAGE ‐ polyculture with 30 prawns/m² free and 40 fish/m³ in net‐cages. Animals, rain, water, feed, soil, gas, accumulated sludge, and suspended sediments were collected throughout the experiment to determine their nitrogen contents and to calculate the nitrogen budget. Results showed that much of the nitrogen available escapes to atmosphere as N₂ (~40%–56%) after denitrification or accumulated within bottom sludge (~14%–42%). The remaining nitrogen was converted in animal biomass (~5%–21%) or was discharged to receiving waterbodies in the outlet water (~11%–13%). Feed management appeared to influence the major biological processes in the aquatic nitrogen cycle, such as photosynthesis and denitrification. The fish‐prawn IMTA systems converted approximately 53%–75% of feed nitrogen into harvestable products, which is more efficient than the 19%–46% of feed nitrogen converted in the monocultures. However, a large amount of nitrogen is accumulated in the pond bottom in all systems. An increased prawn density or the addition of a mud‐feeder species to the culture may enhance the incorporation of this material in harvested biomass, improving the efficiency of the systems.     

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.     

Current status and prospects of farming the giant river prawn Macrobrachium rosenbergii (De Man) in Bangladesh

Giant river prawn (Macrobrachium rosenbergii) farming plays an important role in the economy of Bangladesh. Presently, it is cultured in around 50 000 ha area with total annual production of 23 240 t. Traditional extensive prawn farming has been expanding over the last three decades through the introduction and adoption of improved culture systems, such as culture of prawn‐carps, prawn‐shrimp‐fish and prawn‐fish‐rice as concurrent and rotational systems. Efforts for the development of improved techniques on broodstock management, seed production and rearing and grow‐out of prawn have been made over the last decade. The outcomes are low‐cost feed for broodstock, production of post‐larvae in net cages (hapa), all‐male prawn culture, periphyton based prawn‐tilapia culture, C/N based prawn culture, organic prawn farming, prawn‐mola culture and prawn‐carp‐mola polyculture. Despite the development of culture technologies, a number of challenges for sustainable development of prawn farming need to be overcome to realize the potentials of this promising sector. Good aquaculture practises at all levels and application of measures for quality control and food safety would ensure sustainable development of prawn farming in Bangladesh.     

Economic effects of production scale,use of agricultural greenhouses,and integration of tropical aquaculture species when farming in a subtropical climate

Fresh and local production of tropical fish species are growing in demand in subtropical and temperate regions. However, their productions are limited by the short growing season and uncertainty related to using agricultural greenhouses. Thus, this study evaluated the economic feasibility of Amazon River prawn (Macrobrachium amazonicum) and tambaqui (Colossoma macropomum) grow-outs in monoculture and integrated multi-trophic aquaculture (IMTA) systems carried out in a subtropical region of Brazil, considering the transfer of the fish to agricultural greenhouses to complete the grow-out during the winter season. Simulations were performed of each system on small- (1 ha) and medium (5 ha)-sized properties to test the effects of production system and scale on cost return and cash flow, economic indicators, and sensitivity (risk) to productivity and market changes. Treatments were prawn monoculture (PRWN), tambaqui monoculture (FISH), IMTA of prawns and tambaqui reared free-swimming (IMTA), and IMTA of prawns reared free-swimming and tambaqui reared in net cages (CAGE). Harvested prawns were marketed for recreational fishing and the tambaqui is traded for the next grow-out phase after overwintering in greenhouses. Internal rate of return (IRR), net present value (NPV), payback period (PP), and benefit–cost ratio (BCR) showed economic feasibility for all systems, and shorter PP and greater profitability were observed with an increased size of the properties. In addition, the integrated systems showed resilience by remaining economically feasible when subjected to variations in productivity, major costs, and selling price. Further research should test the technical feasibility of producing tambaqui in greenhouses during the winter in colder climates.

     

Improvement of nutritional quality of live feed for aquaculture: An overview

In hatcheries, the adequate supply of live feed has a vital role in feeding fish larvae, fry and fingerlings. Furthermore, the enhancement of the nutritional quality of live feeds is well‐developed techniques in aquaculture. Essential fatty acids (EFA) such as docosahexaenoic acid (DHA; C22:6 n?3), eicosapentaenoic acid (EPA; 20:5(n?3) and arachidonic acid (ARA; 20:4(n?6) and amino acids are an essential source of proteins for larval rearing of fish. However, the common practised live feeds used for the primary feeding such as rotifers and Artemia are naturally deficient in essential nutrient components. Hence, the improvement of the nutritional quality of live feeds with different oil emulsions and commercial diets, and manipulation of the feed are necessary for fish production. The production protocols of copepods, Moina and fairy shrimps as live feed are still underdeveloped in hatcheries. The different lipid sources using for the enrichment of Artemia and rotifers are not effective on other live feeds, especially copepods and cladocerans (Moina, Daphnia) and fairy shrimps. This review focuses on the importance of live feeds by the techniques of feed enhancement or enrichment of zooplankton by direct incorporation of nutrients for feeding of early stages of fish.     

Demonstration of salmon farming as a net producer of fish protein and oil

To date aquaculture’s reliance on dietary marine sources has been calculated on a fish weight‐to‐weight basis without considering the absolute amounts of nutrients but this approach neglects the often considerable differences in the nutritional value of fish. We propose simple nutrient‐to‐nutrient‐based dependency measures that take into account these nutritional differences. In the first study reported here, individually tagged Atlantic salmon (Salmo salar) were reared in seawater supplied tanks with feed collection facilities. In the second, commercial net pens were used to grow over 200 000 fish. For both studies, a low marine ingredient feed containing approximately 165 g kg^?1 fishmeal was compared to a control feed (approx 300 g kg^?1 fishmeal) whilst fish oil inclusion was less markedly reduced. The low marine feeds supported similar growth and feed efficiency compared to the control feeds. With the low marine ingredient feeds, the weight of salmon protein and lipid produced through growth exceeded the weight of marine protein and lipid consumed by the fish meaning that salmon farming can be a net producer of fish protein and oil. The amount of n‐3 long‐chain polyunsaturated fatty acids deposited was sufficient to meet current recommendations from human health organizations.     

Diet and Food Assimilation by Channel Catfish and Malaysian Prawns in Polyculture as Determined by Stomach Content Analysis and Stable Carbon Isotope Ratios 1

Stable carbon isotope ratios (?³C) and stomach contents were used to determine the diet of channel catfish (Ictalurus punctatus) and freshwater Malaysian prawns (Macrobrachium rosen-bergii) in polyculture. Catfish stomach contents were dominated by formulated rations. Macrophyte fragments and catfish ration were predominate in prawn stomachs. Catfish ?¹³C ratios became lighter from June to October, which paralleled the change in ?¹³C ratio of the formulated feeds fed to the fish. Prawn ?¹³C ratios became heavier from June to October with a change in diet from seston to aquatic macrophytes and formulated catfish feed. Formulated feeds contributed 68-99% of catfish growth, and “natural” pond biota, principally insects, the remainder. Prawns depended to a greater extent on the autotrophic food web for their diet. Seston and macrophytes contributed 18-75% of prawn growth, and formulated feeds the remainder. The prawns fed on seston at small sizes (<7 g) and consumed more aquatic macrophytes and formulated catfish ration at larger sizes (<7 g).     

Spent brewer's yeast as a replacement for fishmeal in diets for giant freshwater prawn (Macrobrachium rosenbergii), reared in either clear water or a biofloc environment

A 90‐day feeding experiment was conducted in order to test spent brewer's yeast as a replacement for fishmeal in diets for giant freshwater prawn (Macrobrachium rosenbergii) reared in either a recirculating aquaculture system (RAS) or a biofloc system. Triplicate groups, each of 20 prawn (6.7 ± 0.03 g), were randomly assigned to 24 identical tanks. Twelve tanks were connected to the RAS, and the other 12 tanks were connected to the biofloc system which were initially supplemented with Bacillus subtilis, molasses and blood meal to achieve a C:N ratio of 20:1. Four iso‐nitrogenous (350 g/kg) and iso‐energetic (19 MJ/kg) diets where 0%, 20%, 40% and 60% of fishmeal protein was replaced by spent brewer's yeast. Neither growth nor survival was affected (p > 0.05) by increasing levels of brewer's yeast. The exception, being fish given 60% replacement with brewer's yeast, reared in biofloc, which displayed a higher (p < 0.05) growth than fish given 40% replacement, reared in clear water. The feed conversion ratio of prawn reared in the biofloc environment was lower than in the clear water. We concluded that spent brewer's yeast represents a possible 60% substitute for fishmeal in giant freshwater prawn diets, especially for prawn reared in a biofloc environment.     

The importance of live‐feed traps – farming marine fish species

This article analyses the challenges of different live‐feed regimes for the rearing of marine finfish larvae and discusses the potential alternative live feeds to avert a future live‐feed trap. Live feeds are indispensable for the successful rearing of larvae of most marine fish species. Brine shrimps (Artemia) and rotifers comprise the live feeds of choice in marine aquaculture today. However, their nutritional composition is deficient in especially essential fatty acids, and enrichment with fish oil is needed. Fish oil is considered a limited resource owing to its origin in fully exploited wild fish stocks. Moreover, fluctuations of the natural population of Artemia will, most likely, influence future availability and prices. This emphasizes the need for optimal exploitation of available live‐feed resources and development of new sustainable alternatives, such as copepods. An array of solutions to these problems are presented to avoid a future live‐feed trap and to reduce dependence on limited resources that influence future production possibilities, species diversification, price volatility and productivity in the aquaculture sector.     

Identification of a putative cellulase gene in the giant freshwater prawn,Macrobrachium rosenbergii (De Man, 1879)

Nutrition plays an important role in the development of all organisms and in particular that of farmed aquatic species where costs associated with feed can often exceed 60% of total production costs. Crustacean species in addition, have the added metabolic requirement for regular moulting to allow normal growth and this requires large amounts of energy in the form of sugars (glucose). The current study explored the capacity of the giant freshwater prawn to produce endogenous cellulose‐degrading enzymes capable of extracting nutrients (simple sugars) from plant sources in formulated feeds used in the prawn aquaculture industry. We identified a putative cellulase cDNA fragment in the target organism of 1576 base pairs in length of non‐microbial origin that after protein modelling exhibited a TM‐score of 0.916 with a described cellulase reported from another crustacean species. The functional role of cellulase enzymes is to hydrolyse cellulose to glucose and the fragment identified in GFP was highly expressed in the hepatopancreas, the site of primary food digestion and absorption in crustaceans. Hepatopancreatic tissue from Macrobrachium rosenbergii also showed active digestion of cellulose to glucose following an endoglucanase assay. Cellulase gene(s) are present in the genomes of many invertebrate taxa and play an active role in the conversion of cellulose to available energy. Identification and characterization of endogenous cellulase gene(s) in giant freshwater prawn can assist development of the culture industry because the findings confirm that potentially greater levels of low‐cost plant‐material could be included in artificial formulated diets in the future without necessarily compromising individual growth performance. Ultimately, this development may contribute to more efficient, cost‐effective production systems for freshwater prawn culture stocks that meet the animal's basic nutritional requirements and that also support good individual growth rates.     

Growth performance,muscle biochemical constituents,amino acid and fatty acid compositions of the giant freshwater prawn,Macrobrachium rosenbergii,fed with herb‐incorporated diet

This study was conducted to evaluate the influence of herbs such as Ocimum sanctum, Phyllanthus amarus and Solanum trilobatum on the freshwater prawn, Macrobrachium rosenbergii, postlarvae (PL). These herbs were powdered and incorporated at 5% with the basal diet separately and in a combination. The M. rosenbergii was fed with these feeds for a period of 90 days. Results indicated that significant (P < 0.05) improvements were observed in the survival, nutritional indices (weight gain, specific growth rate and protein efficiency ratio), proximate muscle biochemical constituents (total protein, amino acid, carbohydrate and lipid), profiles of essential amino acids and fatty acids of prawns fed with herb‐incorporated feeds. Among these herbs supplemented, P. amarus produced significantly (P < 0.05) better performance followed by S. trilobatum and O. sanctum. However, prawns fed with these herbs combination showed an insignificant (P > 0.05) improvement in survival and growth performance when compared to individual supplementation. Hence, this study suggests that the herbs (O. sanctum, P. amarus and S. trilobatum) can be used as a supplementary feed for a sustainable development of freshwater prawn culture.     

Evaluation of freshwater prawn‐small fish culture concurrently with rice in Bangladesh

An integrated aquaculture of freshwater prawn (Macrobrachium rosenbergii) and self‐recruiting small fish mola (Amblypharyngodon mola) was conducted in farmers' rice fields at Mymensingh, Bangladesh. There were four treatments with three replications. Four stocking densities, 10 000, 15 000, 20 000 and 25 000 ha^?1, of freshwater prawn were applied. The stocking density of mola was the same (20 000 ha^?1) in all treatments. During land preparation, triple super phosphate (TSP) and murate of potash (MP) were applied at the rate of 150 and 75 kg ha^?1 respectively. Urea was applied at the rate of 200 kg ha^?1 in equally distributed three installments after 16, 45 and 65 days of rice plantation. Prawns were fed with commercial pelleted feed at 3–8% body weight. All water quality parameters were found to be within the suitable range for freshwater prawn culture. There was a homogenous abundance of plankton communities in all treatments. The results of a 4‐month culture period showed that the average production of prawn ranged from 222 to 388 kg ha^?1, mola 51 to 68 kg ha^?1 and rice 2 880 to 3 710 kg ha^?1. Significantly higher production of both prawn and mola was recorded in the plots where the freshwater prawn stocking density was 15 000 ha^?1. This treatment resulted in a net profit of USD 1100 ha^?1.     

Effects of C/N ratio and periphyton substrates on pond ecology and production performance in giant freshwater prawn Macrobrachium rosenbergii (De Man, 1879) and tilapia Oreochromis niloticus (Linnaeus, 1758) polyculture system

The production performances of giant freshwater prawn Macrobrachium rosenbergii and Nile tilapia Oreochromis niloticus in C/N‐controlled periphyton‐based polyculture systems were evaluated in triplicate. Three different management practices were compared: the traditional practice without addition of periphyton substrates and carbohydrate (Control), addition of maize flour to maintain a carbon: nitrogen rate of 20:1 (treatment CN) and addition of both maize flour and periphyton substrates (treatment CN+P). This experiment used a pre‐optimized stocking density of tilapia and freshwater prawn by Asaduzzaman et al. Aquaculture [286 (2009) 72]. All ponds were stocked with prawn (3 m²) and monosex Nile tilapia (1 m^?2). Bamboo side shoots were posted vertically into the pond bottoms as periphyton substrate covering an additional area of 171 m² for periphyton development. A locally formulated and prepared feed containing 17% crude protein with C/N ratio close to 15:1 was applied twice daily in all ponds considering the body weight of freshwater prawn only. Water quality parameters, except total alkalinity did not vary significantly (P > 0.05) among treatments. Both, organic matter and total heterotrophic bacterial loads (THB) in the sediment were significantly (P < 0.05) higher in treatment CN+P followed by treatment CN and control. Periphyton biomass in terms of dry matter and chlorophyll a values constantly decreased during the culture period. Substrates contributed 66% and 102% higher net yield of freshwater prawn than CN and control treatment respectively.     

海蜇—对虾—缢蛏—牙鲆综合养殖池塘的食物网分析

在面积6.7 hm^2,水深1.5～2.0 m的池塘中进行海蜇—中国明对虾—缢蛏—褐牙鲆综合养殖,在4—9月养殖周期内,采用碳氮稳定同位素法和IsoSource线性混合模型计算各种饵料对海蜇、中国明对虾、缢蛏和褐牙鲆的平均饵料贡献率,以探讨综合养殖池溏的营养级和池塘食物网结构。试验结果表明,海蜇的主要食物来源为投喂的轮虫;中国明对虾的食物来源为鳀鱼、虾夷扇贝下脚料和蜢虾;缢蛏的主要食物来源为底栖硅藻,其次为中国明对虾与褐牙鲆粪便;褐牙鲆的主要食物来源为中国明对虾,其次为虾夷扇贝下脚料和鳀鱼。海蜇的营养级为2.09～3.43,平均值为2.81;中国明对虾的营养级为3.11～4.04,平均值为3.72;缢蛏的营养级为2.37～2.94,平均值为2.62;褐牙鲆的营养级为2.63～3.83,平均值为3.42。综合分析发现,海蜇摄食浮游动物,缢蛏滤食底栖硅藻,中国明对虾和褐牙鲆摄食投喂的虾夷扇贝下脚料和鳀鱼,褐牙鲆也摄食部分中国明对虾,两者的粪便不仅为浮游单胞藻和底栖硅藻生长提供营养,还为缢蛏提供了饵料。上述研究结果为多品种海水综合养殖池塘的生态健康养殖提供科学依据。     

Nutrient composition of fairy shrimp Streptocephalus sirindhornae nauplii as live food and growth performance of giant freshwater prawn postlarvae

Nutritional efficacy of fairy shrimp (Streptocephalus sirindhornae) nauplii, as a live food, was studied for growth performance and survival rate of giant freshwater prawn (Macrobrachium rosenbergii) postlarvae. A feeding experiment was designed with four different feeds: dry commercial feed, fairy shrimp nauplii, Artemia sp. nauplii and adult Moina macrocopa. Results from the nutritional composition revealed that fairy shrimp nauplii had protein and lipid contents of 54.58 ± 2.8 g kg^?1 and 255 ± 2.8 g kg^?1, respectively. The highest value for an individual amino acid in fairy shrimp was lysine (140.7 ± 1.6 g kg^?1). The essential amino acids content in the whole body of the larval prawns was in the range of 66.7–67.5 g kg^?1. Fairy shrimp nauplii had the highest essential amino acid ratio (A/E) of lysine, similarly, in musculature of prawn larvae. Weight gain and specific growth rate of the postlarvae fed with fairy shrimp nauplii were significantly higher than those fed with Artemia nauplii, adult Moina and dry commercial feed. The presented results suggest that S. sirindhornae nauplii can be used as a nutritionally adequate food for freshwater prawn M. rosenbergii postlarvae.     

Use of planted biofilters in integrated recirculating aquaculture‐hydroponics systems in the Mekong Delta,Vietnam

The feasibility of using planted biofilters for purification of recirculated aquaculture water in the Mekong Delta of Vietnam was assessed. The plant trenches were able to clean tilapia aquaculture water and to maintain good water quality in the fish tanks without renewal of the water. NH₄‐N was removed efficiently in the plant trenches, particularly in the trenches with Canna glauca L., probably because of plant uptake and nitrification–denitrification. Plant uptake constituted 6% of N and 7% of P in the input feed. Approximately 1.0 m³ of water was needed per kg of fish produced, and 370, 97 and 2842 g fresh aboveground biomass of Ipomoea aquatica Forssk., Lactuca sativa L. and C. glauca, respectively, were produced. The leafy vegetables provide some extra income besides fish products, whereas C. glauca provides nice flowers and contributes to a significant nutrient removal with annual uptake rates of 725 kg N and 234 kg P ha^?1 year^?1. This research demonstrates that integrated recirculating aquaculture‐hydroponics (aquaponics) systems provide significant water savings and nutrient recycling as compared with traditional fish ponds.     

Effect of time-restricted feeding and refeeding regimes on compensatory growth,body composition,and feed utilization in prawn (Macrobrachium rosenbergii) culture system

ABSTRACT

A 14-week feeding experiment was conducted to determine the effect of a time-restricted feeding and refeeding regime on compensatory growth, body composition, and feed utilization in improved traditional prawn (Macrobrachium rosenbergii) culture systems. Three groups of prawn were used in which the control group (C) received feed regularly at ad libitum and the other two groups, Treatment 1 (T₁) and Treatment 2 (T₂), consumed feed 4 and 5 days per week respectively throughout the first 9 weeks. After feeding restriction, satiation of feed was given in the last 5 weeks. At the end of the experiment, the final weight of prawn in C, T₁, and T₂ were found to be 17.23 ± 6.56g, 16.04 ± 6.18g, and 15.64 ± 6.34 g respectively, which was insignificant. FCR decreased with increased restriction of feeding, while PER and NPU increased. Moisture content increased significantly, while protein and lipid content decreased significantly with increasing restriction time of feeding. After the satiation period, only the T2 group was able to replenish the lipid content. Water quality parameters didn’t vary significantly among the experimental groups and remained within optimum level. Therefore, time restriction could be applied in Macrobrachium rosenbergii culture without detrimental effects on growth, feed efficiency, and nutrient utilization.     

A contingent valuation of the biomitigation benefits of integrated multi-trophic aquaculture in Canada

Integrated multi-trophic aquaculture (IMTA) is the farming, in proximity, of aquaculture species from different trophic levels and with complementary ecosystem functions. IMTA allows one species’ uneaten feed and wastes, nutrients, and by-products to be recaptured and converted into fertilizer, feed, and energy for the other crops. By taking advantage of synergistic interactions between species, IMTA can help aquaculture evolve towards more responsible and sustainable systems. This study uses data from a contingent valuation survey to provide an estimation of the non-use benefits that, in the form of biomitigation of the external costs imposed on the marine environment, would be derived by Canadians from the adoption of IMTA for Atlantic salmon aquaculture. We find the benefits accruing to households who do not purchase salmon habitually would range between about $43 million/year and about $65 million/year for the next five years, depending on the treatment of ‘don’t know’ responses to the payment question.     

Yield characteristics of prawns, Macrobrachium rosenbergii (de Man), with fish polycultures at low feeding rates

Abstract. As currently practiced, freshwater prawn, Macrobrachium rosenbergii (de Man), aquaculture in Hawaii requires large inputs of supplementary feed, water and labour. The high cost of these inputs greatly restricts profit potential. An experiment was conducted to compare an alternative prawn production system which used lower feeding rates and fish polycultures to reduce inputs. Three treatments were run in quadruplicate: (1) control—prawns stocked at standard densities (11.5 per n2) in monoculture and fed standard prawn pellets at the commercial ration recommendations by New & Singholka (1982); (2) low feed—prawns at standard densities and fish [silver carp, Hypophthalmichthys molitrix (Valenciennes), grass carp, Ctenopharyngodon idella (Valenciennes), and grey mullet, Mugil cephalus (L.)] fed one-half commercial ration; and (3) maintenance feed—prawns at standard densities and fish fed one-tenth commercial ration. Although prawn yield characteristics (mean weights, harvestable sizes, survival, net yields) were not significantly different (P > 0.05) based on an analysis of variance in the three treatments over the approximately 9.5-month culture period, this lack of significance most likely resulted from interpond variability and the lack of a large number of replicates. The relatively poor survival (60–63%) of gray mullet and an almost twofold difference in prawn yields in the control and maintenance feed treatments suggest that there was in fact competition for resources in the nominally polyculture systems. Nevertheless, the wet weight yield of biomass from all species was twice as high in the low feed ponds as in the control ponds.     

Effects of replacing dietary fish oil and squid liver oil with vegetable oils on the growth,tissue fatty acid profile and total carotenoids of the giant freshwater prawn, Macrobrachium rosenbergii

A feeding trial was conducted to investigate the complete substitution of either fish oil (FO) or squid liver oil (SLO) with crude palm oil (CPO), canola oil (CO) sunflower oil (SFO) or linseed oil (LO), as the sole added lipid source in diets fed to triplicate groups of giant freshwater prawn, Macrobrachium rosenbergii (initial weight = 0.42 ± 0.01 g) for 6 weeks. Prawns fed the CO or SLO diets showed significantly higher (P < 0.05) specific growth rate than those fed the FO or CPO diets. The feed conversion ratio of the prawns was significantly better when fed the CO diet, compared with the FO, CPO, SFO and LO diets. The muscle eicosapentaenoic acid content of prawns fed the vegetable oil (VO) diets were not significantly different (P > 0.05) from those fed the FO diet, although all VO‐based diets led to a significantly lower docosahexaenoic acid content compared with prawns fed the FO or SLO diet. The whole‐body total carotenoid content was significantly lower for prawns fed the SLO diet compared with prawns on the CO or CPO diets. The successful use of VO instead of marine‐based oils in prawn diets will likely reduce feeding costs associated with M. rosenbergii aquaculture.