Effects of Cobalt-60 Gamma Irradiation on the Production of the Malaysian Prawn Macrobrachium rosenbergii

Lee, N. and T. R. Tiersch, Aquaculture Research Station, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge, LA 70802

Commercial production of the Malaysian prawn Macrobrachium rosenbergii did not start until the early 1960’s when Ling successfully closed the life cycle indoors. This was followed by the success of Fujimura in the late 1960’s in mass rearing of larvae and in pond culture techniques. In spite of these successes, the production of farmed freshwater prawn remains around 3% of total global crustacean aquaculture production. The basic constraint to profitable culture of this species is growth suppression and variation due to social pecking orders. This leads to highly skewed size distributions with large variance necessitating markets for many size classes. High doses of ionizing radiation have been successfully used to induce sterility in some aquatic species, and aquatic animals exposed to low doses of ionizing radiation in some cases showed better survival and growth than unexposed animals. However, the effects of ionizing radiation have not been studies in prawns. In this paper, we evaluate the use of ionizing radiation to improve yield of cultured prawns. Juvenile prawns (4.5 ± 0.5 cm and 0.7 ± 0.2 gm) were irradiated using a Shepherd irradiator (Model 484R) at the LSU Nuclear Science Center. Five doses were chosen (0, 0.5, 1.0, 1.5 and 2.0 krad) because our earlier studies yield total mortality at 2.5 krad and above. Each treatment consisted of 42 animals (equivalent to a density of 60,000/ha) and was replicated four times. Prawns were fed sinking pellets (32% protein) and were raised for 16 weeks in 5,600 L tank (7-m 2 bottom area and 1.2 m depth). At the end of the study, percent survival, weight, total length and morphological characteristics of the prawns were recorded.

Values sharing a superscript letter were not significantly different. The average body weights, total length and percentage of individuals weighing 22 gm and above decreased with increased doses of gamma rays. The number of virgin females increased with increased doses and the number of gravid and open females decreased with increased doses. However, prawns exposed to 0.5 krad of gamma rays have better survival than did the control and other treatments. This resulted in higher production (1,673 kg/ha) at the end of the study (Table 1) which is equivalent to 254 kg/ha more than the control (1,419 kg/ha).

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Texas Chapter of the American Fisheries Society
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