Improved Technology for Freshwater Prawn Seed Production

Japan International Research Center
for Agricultural Sciences
1-1 Ohwashi, Tsukuba, Ibaraki 305-8686, Japan
Tel: (81 29) 838-6630; 838-6330
Fax: (81 29) 838-6371, 2004-09-01

The giant freshwater prawn, Macrobrachium rosenbergii (Fig. 1), has been identified by the Vietnamese government as one of the major target species of the country's aquaculture sector. Until the beginning of 2000, the supply of hatchery-reared M. rosenbergii depended on a few previously established national hatcheries, and did not meet the growing need for commercial prawn. Recognizing this problem as a major factor limiting the development of M. rosenbergii culture in the Mekong Delta, the Japan International Research Center for Agricultural Sciences (JIRCAS) and Vietnam's Cantho University initiated a collaborative research in 1995, and jointly developed a new, improved means of seed production technology for this species.

Larval Rearing and Water Quality Control

The green water model of water quality control was compared with another system used in seed production, the re-circulating water model. Densities of 60-120 larvae per liter were recommended for both models, but the green water model yielded more post-larvae (PL) per liter, varying from 27.8-41.7 PL/liter compared with 18.6-32.9 PL/liter for the re-circulating water model. Moreover, the green water model requires less labor, and is easier to implement in backyard hatching facilities that are likely to be adopted by farmers engaging in prawn-rice culture (Table 1). An example of such kind of hatchery, the Cantho University's mini-hatchery, is shown in Fig. 2.

Based on these results, and the experience of Cantho University collaborators in the field, researchers developed a modified static green water system suitable for the conditions of seed production in the Mekong Delta. In this system, super-saturated seawater from salt fields and freshwater are mixed in appropriate quantities to obtain the desired salinity concentration, and the water is treated for several days with chlorine. Next, in order to create green water, tilapia are stocked for a week in a separate tank to create an environment with planktonic algae bloom and where the water turns green; algal blooms serve as bio-agents that stabilize the environment within the culture tanks. Chlorella is obtained selectively by filtration, and the water is then transferred to tanks to be used for prawn seed production. After the larval prawns hatch, they are reared for nearly 30 days without water change until they metamorphose into post-larvae.

Larval Feeds

In order to bolster prawn larvae survival rates, different feeding diets were designed and evaluated. Experiments illustrated that larvae fed a custard diet formulated from chicken egg yolk, milk powder, and squid oil provided the best results in terms of survival rate and number of post-larvae produced per liter (data not shown). It was also determined that this diet could be further improved by the supplementation of vitamin C and lecithin. The results of these studies showed that vitamin C and lecithin not only increased post-larvae survival rates, but also improved the quality of post-larvae. These results are now used as basis in standard methods of seed production.

Index of Images

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  Figure 1 The Giant Freshwater Prawn, Macrobrachium Rosenbergii

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  Figure 2 Cantho University's Mini-Hatchery

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  Table 1 Survival Rates of Larvae and Final Number of Post-Larvae (PL) Produced under the Re-Circulating Water and Green Water Systems

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