Prawn Yield Research Articles

EVALUATION OF TECHNICAL AND FINANCIAL EFFICIENCY OF THE GIANT FRESHWATER PRAWN Macrobrachium rosenbergii CULTURE IN COCONUT PLANTATION DITCH IN THANH PHU DISTRICT, BEN TRE PROVINCE, VIETNAM

The study was conducted from June to December 2021 to assess the technical – financial aspect and the existing advantages and difficulties of the giant freshwater prawn culture in coconut garden ditch culture by interviewing 32 farming households in Thanh Phu district, Ben Tre Province. The study results showed that the average area for each ditch was 0.38 ± 0.29 ha, with density stocking 4.15 ± 1.21 PL/m2. For prawns were harvested after over 8 months, the prawn yield was 421.08 ± 172.21 ton/ha/crop, the profit was 34.02 ± 14.02 million VND/ha/crop and the benefit ratio was 1.33 ± 0.56 times. The yield and the profits were affected by density stocking and nursing survival rate. Besides the advantages of labor resources, natural conditions, and ease and less risk of giant freshwater prawn culture; however, the system currently faces many difficulties, such as lower nursing survival rate, unguaranteed quality, and quantity of postlarvae, salinity intrusion, unstableproduct market. Therefore, in order to contribute to sustainable aquaculture development, the necessary solutions include (1) providing high quality and quantity of postlarvae; (2) using settling ponds to have active water; (3) building and improving infrastructure, and irrigation systems to prevent salinity intrusion; and (4) finding the product market.

Effects of salinity and alkalinity on growth and survival of all-male giant freshwater prawn (Macrobrachium rosenbergii De Man, 1879) juveniles

All-male giant freshwater prawns (AMGFPs) have been a popular crop cultivated in the Mekong Delta, Vietnam, due to their proven production efficiency compared to all-female or mixed-sex prawn cultures. However, the crucial water quality factors impacting AMGFP aquaculture efficiency have yet to be elaborately investigated. Two separate experiments were randomly arranged with three replicates to evaluate the effects of salinity or alkalinity on the growth and survival of AMGFP juveniles during the grow-out period. The results show that the prawn survival rate in the salinity range of 0–15‰ varied from 66.1 to 74.8％ and in a salinity range of 0–5‰ was relatively low compared to the range of 10-15‰; however, the difference was not significant among salinities after 90 days of culture (p > 0.05). All the prawn growth performance parameters significantly decreased with increasing salinities of 0, 5, 10, and 15‰ after 30, 60, and 90 days of culture (p < 0.05). Notably, the prawn yield did not significantly differ between salinities of 0 and 5‰ (p > 0.05), and both were significantly higher than those at salinities of 10 and 15‰ (p < 0.05) after 90 days of culture. In addition, the survival rate reached 82.5–84.4％ and did not significantly differ among alkalinities of 80, 100, 120, 140, and 160 mgCaCO3 L−1. However, the growth performance parameters and yield of AMGFPs at an alkalinity of 160 mg L−1 were significantly higher than those at lower alkalinities (80, 100, 120, and 140 mg CaCO3 L−1) after 90 days of culture. Therefore, it is recommended that a salinity range of 0–5‰ and alkalinity of 160 mgCaCO3 L−1 is optimal for the growth-out culture of AMGFP juveniles.

Effect of stocking density on growth performance and gonadal maturity of all‐female giant freshwater prawn, Macrobrachium rosenbergii

AbstractAll‐female stocks of giant freshwater prawn, Macrobrachium rosenbergii, hold immense potential for aquaculture but early sexual maturity might still be a constraint in all‐female prawn farming. The growth performance and gonadal maturation of all‐female M. rosenbergii reared in 1,000 L tanks for 60‐days were tested at five stocking densities of 4 (T1), 8 (T2), 16 (T3), 24 (T4), and 32 (T5) prawns/m2 in triplicates. The mean initial weights (±SD) of prawns were 5.20 ± 0.42 g (T1), 5.10 ± 0.48 g (T2), 5.18 ± 0.54 g (T3), 4.87 ± 0.92 g (T4), and 5.05 ± 1.09 g (T5), respectively. The survival rate (83.3%), mean final weight (24.93 g), daily weight gain (0.33 g), and specific growth rate (2.61) were the highest in T1, while the most efficient feed conversion ratio (1.57) was in T2. The prawn yields were higher at higher stocking densities (T3 to T5). The stocking density of 8 prawns/m2 is feasible for good growth performance, while the estimated density for optimum yield was 23.5 prawns/m2, indicating that all‐female prawns are amenable to intensive farming. The presence of virgin females ranged from 30% in T1 to 14% in T5, but the distribution of ovarian stages was not significantly different among the stocking densities tested. The gonadosomatic index values showed no significant difference among the treatments. The results indicated that while the stocking density significantly affected growth parameters, it had no significant effect on the all‐female prawns' gonadal maturation.

ANALYSING TECHNICAL AND FINANCIAL ASPECTS OF GIANT FRESHWATER PRAWN Macrobrachium rosenbergi (De man, 1879) CULTURE IN BRACKISH WATER AREA OF TRA VINH PROVINCE

This study was conducted through the interview of 48 households applying alternative system of the giant freshwater prawn and shrimp farming in Tra Vinh province. The study aimed to evaluate the effects of different factors on the efficiency of the prawn farming in order to contribute to sustainable development ofthe faming system in the brackish water area of the Mekong Delta. The results showed that the pond was in average area of 0.8 ha; water salinity varied in range of 1-10 ppt during prawn farming. Prawn stocking density was 9.0 inds./m2, and all of the prawn were fed with pellet feed or combined with by-products andtrash fish. After 5, 6 months of culture, average prawn yield of 886 kg/ha/crop and net income of 68 millions VND/ha/crop were achieved. Prawn farming covered only 28.5% of total production cost of the whole system including prawn and tiger shrimp but contributed up to 44.1% of total net income of the prawn -tiger shrimp system. A total of 89.6% of prawn farming households succeeded in getting net income, compared to 81.3% for tiger shrimp farming households. Inaddition, the study also found that factors such as water salinity, pond preparation, seed nursing and feeding methods strongly affect to the efficiency of prawn farming. The result indicated the great potential and feasibility for farming giant freshwater alternatively with tiger shrimp in brackish water areas of the Mekong delta.

Phân tích khía cạnh kỹ thuật và hiệu quả tài chính của mô hình nuôi tôm càng xanh - lúa luân canh với tôm sú ở v

This study was conducted in 2013 through the interview of 60 households applying the giant freshwater prawn - rice - tiger shrimp farming systems in Bac Lieu province. The study aimed to evaluate the effects of different factors on the efficiency of the prawn farming in order to contribute to sustainable development of faming system in the brackish water area of the Mekong Delta. The results showed that the farms were in average area of 2.2ha; ditch area of 29.1% of total farm area. Water salinity of the farming region during the cropping season were in range of 2-10ppt. Prawn seeds were stocked at average density of 1.1 inds/m2, and only 50% of the prawn farms were fed with by-products or trash fish. After 6-8 months of culture, average prawn yield of 110 kg/ha/crop and net income of 11.5 millions VND/ha/crop were obtained. Prawn farming covers only 11.8% of total production cost of the whole system including prawn, rice, and tiger shrimp but contribute up to 22.7% of total net income of the prawn-rice-tiger shrimp system. Short grow-out period, prawn seed nursing, supplementary feeding and partial harvest improved the efficiency of the farming. Water salinity in the range of 2-10 ppt did not affect significantly on prawn yields but higher salinity (5-10 ppt) improved the cost-benefit ratio. The results indicated this system could be good potential for further development.

Performance evaluation of concurrent rice-fish-prawn culture with and without cull harvesting

This study was carried out in farmers' fields for three experimental culture cycles to evaluate the performance of rice–fish–prawn culture. The treatments carried out were deepwater rice mono-cropping (R), and rice–fish–prawn culture with cull harvesting (R–FC) and without cull harvesting (R–F). Water pH and total alkalinity were significantly higher (P<0.05) in R–FC than in R–F, while the concentrations of total suspended solids, plankton and chlorophyll a were higher in R–F. Cull harvesting in R–FC had no marked influence on the concentrations of dissolved oxygen, NH4+, nitrite, nitrate and phosphate compared with the R–F treatment. The significantly higher fish and prawn yields (P<0.05) and species-wise faster individual growth performance in R–FC than in R–F were probably due to periodic cull harvesting, which minimized the competition for food and space as well as physiological stress at reduced density. The paddy yield and percentage increase in paddy yield over rice mono-crop was significantly higher (P<0.05) in R–FC (25%), followed by R–F (16.9%), probably due to lower chlorophyll a (36.7 mg m−3) and plankton density (1.4 × 104 L−1), which minimized the competition for nutrients with rice plants. The highest rice equivalent yield (38.5), output value–cultivation cost ratio (1.56) and enhanced net return (28%) in deepwater rice–fish culture were recorded when cull harvesting was practiced.

Growth and Yield of &lt;i&gt;Macrobrachium malcolmsonii&lt;/i&gt; (H. Milne Edwards) and Carps in Mono- and Polyculture in Rural Area

The study was carried out on mono- and polyculture of freshwater prawn Macobrachium malcolmsonii stocked with different size carp seed (Labeo rohita, Catla catla, Hypophthalmichthys molitrix and Ctenopharyngodon idella) in tropical village fish ponds of Orissa. Treatment-I (T-I) was stocked with M. malcolmsonii juveniles for monoculture. Treatment-II, III and IV were stocked with carp fry, fingerlings and yearlings, respectively with prawn juveniles. M. malcolmsonii juveniles were stocked @ 50,000/ha for monoculture and @ 25,000/ha for polyculture. Carp fry were stocked @ 30,000/ha and fingerlings and yearlings each @ 3,000/ha. Prawns and carps were fed @ 3-5% of the body weight daily with commercial feed. Grass carps were fed with chopped cabbage leaves daily ad libitum. Prawns and carps were harvested at 195 days of rearing. The survival of carps in T-IV was significantly higher (P&lt;0.01) than in T-II and T-III. As stocking size of the carps increased, the final net weight and yield contribution increased. Significant variation (P&lt;0.01) in net fish yield was observed among the treatments. In mono culture (T-I) the prawn production was highest (973.02 kg/ha/yr). In polyculture total prawn yield was 481.64-775.38 kg/ha/yr with the contribution of 21.65-58.68% to total yield. T-IV showed better performance in terms of fish and prawn production compared to T-II and T-III, suggesting the suitability of stocking the carp yearlings with prawn juveniles for polyculture.

The On-Farm Trials of the Rotational Prawn-Rice Farming in a Semi-Deep Water Area

ABSTRACT The on-farm trials of rotational rice-prawn farming in a semi-deep water area in the Mekong Delta of Vietnam was carried out in six rice fields (0.7–1.0 ha) to evaluate the production and economic efficiency of using low and high cost feed on prawn culture in paddies at different densities. Two stocking densities of 4 and 5 PL/m2 were investigated. Two treatments of feed types (pellets only or a combination of pellets, trash fish, and snail meat) were applied at stocking 4 PL/m2. At the treatment of 5 PL/m2, prawns were fed a combination of pellets, trash fish, and snail meat. Prawns were stocked in the mid-April and harvested in mid‐November before the next dry season rice crop. Rice farming was started 3 to 5 days after prawn harvesting. By cull harvesting during the culture period, final mean weights of prawn ranged from 47.2 to 57.2 g/prawn and the male:female ratio at harvesting was 2.5:1.0. The prawn yield of treatment 5 PL/m2 was highest (630 ± 22 kg/ha). Net profits in treatments using the combination of pellets, trash fish, and snail meat were 861 ± 193 US$/ha to 1,019 ± 25 US$/ha for the prawn crop and 1,393 ± 71 US$/ha to 1,576 ± 180 US$/ha for the whole system (prawn crop + dry rice crop) and significantly higher than in treatment using pellet only (P < 0.05). Prawns fed on pellets or a combination of pellets and snail meat both offer similar results in terms of production and economics. The dry rice crop offered high cost benefit ratio (2.29–2.33) with low operating cost (414–434 USD/ha) and it made a better use in sustainable rice fields through the rotational rice-prawn system.

The potential of mixed culture of genetically improved farmed tilapia (Oreochromis niloticus) and freshwater giant prawn (Macrobrachium rosenbergii) in periphyton-based systems

The production performance of genetically improved farmed tilapia (GIFT, Oreochromis niloticus) and freshwater prawn (Macrobrachium rosenbergii) in periphyton-based systems were studied in farmers' ponds at Mymensingh, Bangladesh. Fifteen ponds (200-300 m2 area and 1.0-1.5 m in depth) were used to compare five stocking ratios in triplicate: 100% GIFT, 75% GIFT plus 25% prawn, 50% GIFT plus 50% prawn, 25% GIFT plus 75% prawn and 100% prawn. Ponds were stocked at a total density of 20 000 GIFT and/or prawn ha -1. Bamboo poles (mean diameter 6.2 cm and 5.5 pole m-2) were posted in pond bottoms vertically as periphyton substrate. Periphyton biomass in terms of dry matter (DM), ash-free DM and chlorophyll a were significantly higher in ponds stocked with prawn alone than in ponds with different combinations of GIFT and prawn. Survival of GIFT was significantly lower in ponds stocked with 100% GIFT (monoculture) whereas, that of prawn was significantly higher in its monoculture ponds indicating detrimental effects of GIFT on prawn's survival. Individual weight gains for both species were significantly higher in polyculture than in monoculture. The highest total fish and prawn yield (1623 kg GIFT and 30 kg prawn ha-1) over 125-140 days culture period was recorded in ponds with 75% GIFT and 25% prawn followed by 100% GIFT alone (1549 kg ha-1), 50% GIFT plus 50% prawn (1114 kg GIFT and 68 kg prawn ha-1), 25% GIFT plus 75% prawn (574 kg GIFT and 129 kg prawn ha-1) and 100% prawn alone (157 kg ha-1). This combination also gave the highest economic return. Therefore, a stocking ratio of 75% GIFT plus 25% prawn at a total density of 20 000 ha-1 appeared to be the best stocking ratio in terms of fish production as well as economics for a periphyton-based polyculture system

River pen culture of giant freshwater prawn Macrobrachium rosenbergii (De Man) in southern Vietnam

A technical and socio-economic survey conducted in the Dong Thap province of Vietnam to assess the current status of river pen culture of giant freshwater prawn Macrobrachium rosenbergii (De Man) showed that pen culture, which has been developed and operated by farmers' indigenous knowledge, requires more study in order to optimize stocking density and to assess its environmental impacts. In this study, the prawn pens were of rectangular shape, with an average size of 209 m2. Prawns were stocked in June at an average density of 62 pieces m−2 and fed on farm-made feed and were harvested 2–4 times starting from 4 months after stocking until late December or the following January. The average prawn yield was 0.52 kg m−2 year−1, ranging from 0.14 to 1.6 kg m−2 year−1. The average net return was US$0.71 m−2 year−1, ranging from US$1.24 to 4.37 m−2 year−1. About 73% of the farmers achieved positive net returns. The top five constraints for prawn pen culture were lack of knowledge of culture technologies, poor water quality, disease problems, poor quality of wild seed and lack of capital. Almost all farmers have no environmental awareness, and environmental regulations for prawn pen culture have not been established. Field measurements showed that all measured water quality parameters were within the range for good growth of giant freshwater prawns, and indicated that there was no significant accumulation of nutrients and organic matter at the bottoms of rivers or canals.

Growth and Yield Performance of Fish and Prawn in Rice Field Refuge at Different Stocking Densities and its Impact on Rice Equivalent Yield of Rice-Fish Integration System

This study was carried out to evaluate growth performance of fish and prawn at different stocking densities and its impact on rice equivalent yield (REY) of rice-fish integration system. Growth performance of all species decreased with increase in stocking density from 15000 to 35000/ha. Fish and prawn yield was however, higher (p &lt; 0.05) in refuges with 10 cm weir height plots, irrespective of stocking density while, overall yield performance was good at stocking density of 25000/ha. Moreover, as stocking density increases, carrying capacity remains largely the same and density-dependent growth occurs. Biomass at harvest was more consistent regardless of stocking density. REY was 3.88 - 4.22 t/ha at stocking density of 15000/ha and improved further (3.95 - 4,43 t/ha) when stocking density increased to 25000/ha and recorded no significant increase thereafter, when stocking density increased to 35000/ha.

Stock-recruitment relationships of the tiger prawns (Penaeus esculentus and Penaeus semisulcatus) in the Australian northern prawn fishery

This paper investigates the stock-recruitment and equilibrium yield dynamics for the two species of tiger prawns (Penaeus esculentus and Penaeus semisulcatus) in Australia's most productive prawn fishery: the Northern Prawn Fishery. Commercial trawl logbooks for 1970-93 and research surveys are used to develop population models for these prawns. A population model that incorporates continuous recruitment is developed. Annual spawning stock and recruitment indices are then estimated from the population model. Spawning stock indices represent the abundance of female prawns that are likely to spawn; recruitment indices represent the abundance of all prawns less than a certain size. The relationships between spawning stock and subsequent recruitment (SRR), between recruitment and subsequent spawning stock (RSR), and between recruitment and commercial catch were estimated through maximum-likelihood models that incorporated autoregressive terms. Yield as a function of fishing effort was estimated by constraining to equilibrium the SRR and RSR. The resulting production model was then used to determine maximum sustainable yield (MSY) and its corresponding fishing effort (fMSY). Long-term yield estimates for the two tiger prawn species range between 3700 and 5300 t. The fishing effort at present is close to the level that should produce MSY for both species of tiger prawns. However, current landings, recruitment and spawning stock are below the equilibrium values predicted by the models. This may be because of uncertainty in the spawning stock-recruitment relationships, a change in carrying capacity, biased estimates of fishing effort, unreliable catch statistics, or simplistic assumptions about stock structure. Although our predictions of tiger prawn yields are uncertain, management will soon have to consider new measures to counteract the effects of future increases in fishing effort.

Treatment and reuse of water for prawn cultivation

An experimental prawn pond of 600 sq m surface area and 2 m depth was used for the cultivation of tiger prawn. Thirty-thousand 14-day PL flies were stocked. Water treatment systems consisting of primary sedimentation, aerated biofilter and inclined plate final sedimentation were installed for treatment and recycling of the pond water. With complete recycling and reuse of the pond water and occasional replenishing with seawater to make up for losses due to evaporation, water quality was maintained at an acceptable level. Survival rate of the prawn was above 80 %. Prawn yield was estimated to be around 7.6 tonnes/hectare-cycle or 22.8 tonnes/hectare-year.

Effects of manure fertilization frequency on pond culture of the freshwater prawn, Macrobrachium rosenbergii (de Man)

. The effects of the frequency of manure application (twice weekly, weekly and fortnightly) on prawn production and pond dynamics in culture of Macrobrachium rosenbergii (de Man) were assessed. Juvenile freshwater prawns were cultured for 100 days using pelleted feed and organic fertilizer. Results showed that the greatest (but not significantly different) marketable prawn yield was achieved with fortnightly manuring, but the most stable pond environment as based on oxygen dynamics, developed with weekly fertilization. The highest concentrations of chlorophyll, nitrogen and phosphorus occurred with fortnightly applications, but so too did the lowest ratio of gross primary production: respiration. System dynamics are discussed.

Yield of Penaeus monodon Fabricius in brackishwater ponds given different fertilizer combinations

Yields of Penaeus monodon Fabricius in brackishwater earthen ponds were determined using different fertilizer combinations in two sets of experiments. Results indicated that the use of fertilizers was vitally needed to sustain growth of shrimps at a stocking density of 5000 individuals/ha. Application of urea (45-0-0) and diammonium phosphate (18-46-0) fertilizers at nitrogen to phosphorus fertilizer rates (N:P 2O 5) of 15:15 and 30:15 kg/ha, together with 1 t/ha of chicken manure, was inexpensive and resulted in better yields. In another experiment, increase in the amount of nitrogen and phosphorus fertilizers did not significantly improve prawn yields, but did increase the cost of production. Different salinity levels affected survival in both experiments.

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.

Polyculture of the freshwater prawn Machrobrachium rosenbergii in intensively manured ponds, and the effect of stocking rate of prawns and fish on their production characteristics

Polyculture of freshwater prawns with common carp, tilapias, and various Chinese carps was investigated in four tests, each carried out in 20 or more earthen ponds. In the first test, survival and growth rates of prawns were low in most of the experimental ponds. In three further tests, in which prawn stocking rate was varied over a total range of 5000 to 40 000 prawns per ha, high prawn survival and growth were obtained. Fish stocking varied between 8500 and 17 000 per ha, the major variable being tilapia stocking rate. The results showed that the growth and survival of fish and prawns are independent. Prawns were influenced only by their own stocking rate, which correlates positively with yield and negatively with individual growth. Prawns were not influenced by the species of fish co-stocked with them, the stocking rate of the fish, nor by differences in feeding or manuring regimes. Growth of fish was affected by their own stocking rates and by differences in the nutrient regime (particularly common carp) but not by prawn stocking rates. Fish yields obtained were close to 40 kg/ha per day, while those of prawns increased from 1.6 to 7.2 kg/ha per day with increasing stocking rate. Mean weight of prawns decreased (from 40 g to 24 g) as stocking rates increased and so did the proportion of prawns of marketable weight. For growth periods of 104 to 118 days, as in these tests, optimal prawn stocking rate appeared to be about 20 000/ha. Fish and prawn yields obtained were between 2.5 and 3 times higher than those in other prawn-fish polyculture studies carried out in temperate climates. High density stocking of common carp, tilapia hybrids, Chinese carps and prawns, with manure as the major nutrient input and supplemental feeds in relatively small amounts, is considered a rational aquaculture technique.

POLYCULTURE OF CHANNEL CATFISH,Ictalurus punctatus, WITH POST‐LARVAL AND JUVENILE PRAWNS,Macrobrachium rosenbergii

ABSTRACTPost‐larval (0.01 g) and juvenile (0.2 g) Malaysian prawns (Macrobrachium rosenbergii) were stocked with channel catfish (Ictalurus punctatus) fingerlings (66 9) in earthen ponds. Prawns and catfish were stocked at densities of 4,940 per ha and 7,410 per ha respectively. There were five treatments: replicated ponds stocked with post‐larval prawns and channel catfish; post‐larval prawns only, juvenile prawns and channel catfish, juvenile prawns only, and catfish only. Prawns and catfish were stocked on 26 June and harvested 107 days later on 10 October. Prawn survival in ponds without catfish averaged 90%. This was significantly higher (p&lt; 0.05) than survival of prawns in ponds with catfish (81%). Prawn yield averaged 192 kg per ha in ponds without catfish. This was significantly higher (p&lt; 0.01) than the 124 kg per ha of prawns harvested from ponds with catfish. There were no significant differences (p&gt; 0.05) in prawn survival, average size of prawns at harvest, and prawn yields between prawns stocked as postlarvae and prawns stocked as juveniles. There were no significant differences (p&gt; 0.05) in catfish survival, average weight of catfish at harvest, and catfish yields among all treatments. Catfish survival averaged 83%; the average weight of catfish at harvest was 315 g, and the average catfish yield was 1,968 kg per ha. The good prawn survival, and the fact that prawns reached large sizes (30 g+) in a growing season that could have been extended by 40 days, indicates that there may be a potential for the integration of prawns into catfish farming.

RICE STRAW AS A FEED SUPPLEMENT FORMacrobrachium rosenbergiiIN PONDS

ABSTRACTA pilot study was conducted to evaluate air dried rice hay as a detrital feeding substrate for culture ofMacrobrachium rosenbergii.Six 0.13 ha earthen ponds were stocked with post‐larval prawns at a rate of 30,000/ha on 25 May 1982. Two ponds received rice hay biweekly at 9.8 g/m2/week; two ponds received a pelleted ration 5 days/week at 6.2 g/m2/week, and two ponds received both rice hay at 9.8 g/m2/week and the pelleted ration at 3.1 g/m2/week. “Boom and bust” phytoplankton cycles prevailed in ponds receiving rice hay, and sub‐lethal dissolved oxygen levels resulted in reduced prawn survival in ponds. One hay‐only pond had complete prawn mortality due to a sudden die‐off of an algal bloom. Prawns were harvested 12 October after a 133‐day grow‐out period. Prawn yield from a single hay‐only pond was 439 kg/ha; survival was 97.5% and individuals averaged 15 g. Prawn yield in the pellet‐only treatment averaged 600 kg/ha; survival was 90% and individuals averaged 22 g. Prawn yield in ponds receiving both hay and pellets averaged 427 kg/ha; survival was 48%, and individual prawns averaged 29 g. Rice hay or similar agricultural by‐products may have promise as detrital forage to supplement pelletized rations in prawn culture ponds, but further research is required to quantify optimum loading rates, nutritional contribution, and effects on water quality.

Production of the freshwater prawn Macrobrachium rosenbergii in Israel : I. Integration into fish polyculture systems

Two major problems observed in prawn monoculture can be solved using polyculture with fish: 1. (a) The introduction of low stocking densities of common carp, silver carp and grass carp is shown to prevent undesired unicellular or multicellular algal blooms and to improve the oxygen regime. No effect on prawn yield characters is observed, while the marginal fish yield improves the profitability of the pond. 2. (b) The low average weight and the wide size distribution of prawns stocked at high densities are avoided in a strategy of marginal prawn production with high stocking densities of common carp, Tilapia sp. and mullet in commercial ponds. Stocking of prawns at a low density of about 5000 ha −1 results in 90% of the prawns growing to the large market size (>45 g) within 130 days, a survival rate of 43–96% and yields of 96–312 kg ha −1. Since prawns grow on natural productivity alone, and the production costs are shared, prawn yields at such levels are highly profitable.