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* ICLARM is now known as WorldFish Center

Naga - The *ICLARM Quarterly
Vol. 24, No. 3 & 4 (July – December 2001)

Aquabyte
The Half-lives of Biological Activity of some Pesticides in Water
Kyaw M.O.

Abstract
In the absence of analytical methods, the half-lives of biological activity of pesticides can be estimated by bioassays. To determine the half-lives of biological acivity of pesticides to fish, static bioassays were conducted in the laboratory with ten different formulations of pesticides using Labeo rohita as a bio-indicator. The half-lives of biological activity for ten different pesticides in soft water at pH 7.5 and 27C, ranged from 4.6 days to 11.8 days. The half-life of biological activity of Sumithion 50% EC was only 4.6 days. In contrast, Dimecron 50% EC degraded very slowly and its half-life of biological activity on L. rohita was about 11.8 days. Sumithion 50% EC, Padan 50% SP, EPN 45% EC, Diazinon 40% EC and Diazinon 10 G degraded in less than five to seven days indicating that these pesticides are desirable for rice-fish culture. Contamination by pesticides with long-term residual toxicity in waters may eventually cause high levels of fish mortality.

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A Note on Monoculture of Penaeus monodon in a Hardwater Seasonal Pond
S. Athithan, T. Francis, N. Ramanathan and V. Ramadhas

Abstract
A study was undertaken to assess the growth performance of brackishwater tiger shrimp, Penaeus monodon under monoculture in a hardwater seasonal pond in Tamil Nadu, India. A production of 209 kg/ha/110 days was attained at a low stocking density of 1.5/m2.

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White Spot Viral Desease in Penaeid Shrimp - A Review  
A.P. Sangamaheswaran and M.J.P. Jeyaseelan

Abstract
The white spot viral disease in penaeid shrimp affects the development of the global shrimp industry. This paper reviews the viruses that cause the disease, the transmission of the virus, diagnosis and preventive measures.

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