Low-input Modified Extensive Shrimp Culture System for Penaeus monodon Restrian Vibriosis
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It was hypothesized that an outbreak of vibriosis can be restrained in ponds with a low stocking density (~5 post-larvae m<sup>-2</sup>) till harvest. Therefore, during a 135 day production cycle of Penaeus monodon at an aquaculture facility, we monitored (i) physico-chemical parameters (ii) abundance of total heterotrophic bacteria (THB), total Vibrio like organisms (TVLO) and luminescent bacteria (LB) (iii) alterations in environmental factors controlling Vibrio abundance and (iv) changes in composition of the Vibrio community. Physico-chemical parameters were within the optimum range recommended for culture of P. monodon. In source and pond water, THB abundance remained steady at 10<sup>3</sup> CFU mL<sup>-1</sup> throughout the culture period whereas in sediments, they varied between 10<sup>2-4</sup> CFU g<sup>-1</sup>. The abundance of TVLO and LB in pond components were below the threshold levels of 10<sup>4</sup> CFU mL<sup>-1</sup> and 10<sup>2</sup> CFU mL<sup>-1</sup> respectively. THB, TVLO and LB were more abundant in the shrimp hepatopancreas (10<sup>5</sup> CFU g<sup>-1</sup>) yet apparently below the threshold for the outbreak of vibriosis in the current set up. Changes in bacterial abundance were seemingly independent of changes in environmental parameters suggesting that the systems maintained TVLO below disease-causing threshold. The Vibrio community was represented mainly by V. metschnikovii, V. fluvialis, V. mimicus and the closely related Aeromonas spp. The vibrios in shrimp hepatopancreas were similar to other pond components with no dominance of particular species. A disease-free environment prevailed and shrimp yield was sustainable within the set framework perhaps due to the low abundance of vibrios represented by innocuous strains.
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