Impact of Different Management Technologies on the Production, Population Structure, and Economics of Freshwater Prawn Macrobrachium rosenbergii Culture in Temperate Climates

In temperate zone ponds, maximization of total production without decreasing average harvest weight is of increased importance due to the relatively short growing season. Recent research on the freshwater prawn Macrobrachium rosenbergii has shown that techniques such as size grading juveniles and adding artificial substrate to the ponds can accomplish these goals, and their impacts appear to be cumulative. However, due to the greater investments required, private producers have been reluctant to adopt these practices. The studies involved in developing these independent technologies have been conducted over a number of growing seasons with their different environmental conditions. It is important that different production technologies being utilized by commercial producers be directly compared under standardized conditions. The objective of this study was to compare the previously recommended and widely used technology (39,200/ha; ungraded juveniles; no substrate) (Low Input) with an intensified version of that technology used by some producers (54,340/ha; ungraded juveniles; no substrate) (Medium Input) with a technology package developed through a series of research trials to maximize production (69,160/ha; graded juveniles; with substrate; phase feeding) (High Input) under standardized conditions. Each of the seven 0.04-ha ponds were randomly assigned to either the Low Input, Medium Input, or High Input treatment with two, three, and two replicate ponds per treatment, respectively. Juvenile prawns (ungraded 0.6 ± 0.3 g; graded 0.9 ± 0.3 g) were stocked at one of the three densities according to its randomly assigned treatment. Low and Medium Input ponds received no added substrate while artificial substrate was added to the High Input ponds a rate sufficient to increase available surface area by 50%. Low and Medium Input Treatments were fed a 32% protein sinking pellet according to a feeding table. High Input ponds were fed at rates 20% above the feed table recommendations. After 104 d, survival was significantly higher (P± 0.05) in the High Input treatment (92%) than in the Medium Input treatment (83%), with Low Input ponds being intermediate (88%). Compared to the Low Input technology, the Medium Input technology significantly increased (P± 0.05) total production but significantly reduced average weight, so that Production Stock Index (PSI) and production of marketable size animals (> 20 g) or premium size animals (> 30 g) was not significantly increased (P > 0.05). Compared to the original Low Input technology, the High Input treatment significantly increased (P 20 g) (140%), production of premium size animals (> 30 g) (130%), and feed efficiency (32%). The move from the Low Input technology to the High Input technology reduced breakeven costs by 13% based on operating costs and 22% based on total cost figures. In summary, adoption of the High Input technology appears to be biologically and economically justified if similar results can be obtained in commercial scale ponds.