In order to develop an environment-friendly aquaculture system utilizing the natural purification capabilities and high productivity of mangrove brackish waters, water was circulated between aquaculture ponds and mangrove enclosures ( Fig. 1).
Water was circulated between shrimp aquaculture ponds stocked with 10,000 or 20,000 PL-15 stage Penaeus monodon, and mangrove enclosures were planted with 476 Rhizophora mucronata per enclosure ( Fig. 2). About 30% of the water in Ponds 2 and 5 was moved to the mangrove enclosures (Ponds 3 and 4, respectively) every Thursday, and the same amount was returned to the shrimp ponds every Monday.
The survival rate ( Table 1) was significantly higher (P < 0.001, Fisher's exact test) in Pond 5 where 10,000 larvae were stocked and water was exchanged with the mangrove enclosure compared to the control pond; the feed conversion ratio was lowest in Pond 5.
Only 11-15% of phosphorus was incorporated into the shrimp bodies; P content in the mud exceeded the amount provided in the feed in Pond 1 ( Table 2), and the P budget was negative. This suggests that extra P was supplied from another source. We believe that anoxia was responsible for the release of P from the lower depths of the ponds. In Pond 2, the budget results suggest that 1.55 kg of P flowed into the mangrove-planted pond. Although the budget results were negative in Pond 5, it was higher than that of Pond 1. If the same quantity of P in Pond 1 had been supplied in Pond 5 from the lower depths of the pond, about 0.43 kg of P should have flowed into the mangrove ecosystem.
Effectiveness of This System
Pond 5 achieved the most efficient level of aquacultural production; the deterioration in the lower pond environment was reduced in Ponds 2 and 5 via the circulation of water between the shrimp and mangrove ponds, in comparison to the control. Because the P budget was higher in Ponds 2 and 5 relative to the control, environmental burden in the ponds was reduced.
Cooperating agency for this topic:
Japan International Research Center for Agricultural Sciences
and Ishigaki Tropical Station, Seikai National Fisheries Research Institute, Fisheries Research Agency
Index of Images
Table 1 Stocked Larvae, Total Weight of Shrimp, Number of Individuals at Harvest, Survival Rate, Average Shrimp Size, Amount of Feed during the Experiment, and Food Conversion Ratio (FCR)
Figure 1 Mangrove Enclosure
Figure 2 Schematic Outline of Shrimp Aquaculture Ponds and Mangrove Enclosure
Table 2 Phosphorus Budget (KG/Pond/Experimental Period) in Shrimp Aquaculture Ponds during the 136-Day Experimental Period
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