Effect of Intensification on Grow Out of the Amazon River Prawn, Macrobrachium amazonicum

The effects of intensification on growth, survival, productivity, population structure, and distribution of harvested biomass in individual size classes of Macrobrachium amazonicum in semi‐intensive culture were evaluated. Postlarvae (0.01 g) were stocked in 12 ponds at densities of 10, 20, 40, and 80/m² (three replicates per treatment) and raised for 5.5 mo. Average individual weight significantly decreased and productivity significantly increased as stocking density increased (P < 0.001), while survival was not affected (P > 0.05). Prawn mean weight at harvest ranged from 3.6 (80/m²) to 7.0 g (10/m²). Average survival ranged from 65.5% (40/m²) to 72.8% (20/m²), while productivity ranged from 508 (10/m²) to 2051 kg/ha (80/m²). Harvested biomass showed a clear bimodal distribution in individual size classes indicating the occurrence of heterogeneous growth, which may affect management and market strategies. Harvested biomass of prawns weighing more than 7 g (the best market size) increases for stocking densities up to 40/m² and stabilizes between 40 and 80/m². Growth reduction was associated with a decreasing frequency and average weight of green claw 1 and green claw 2 male morphotypes and adult females as density increased. Thus, the distribution of male morphotypes and sexually mature females are affected by density‐dependent factors. Results suggest that prawn density plays an important role on M. amazonicum grow‐out phase, as has been demonstrated for other species of the genus Macrobrachium. M. amazonicum tolerates grow‐out intensification and may be raised in both semi‐intensive and intensive systems stocked at very high densities yielding high productivity.     

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.