SLUDGE MANAGEMENT IN INTENSIVE POND CULTURE OF SHRIMP - EFFECT OF MANAGEMENT REGIME ON WATER-QUALITY, SLUDGE CHARACTERISTICS, NITROGEN EXTINCTION, AND SHRIMP PRODUCTION

Formation and accumulation of sludge in intensive ponds is generally p erceived to impact shrimp production, although there have been few sys tematic investigations. Sludge deposits are suspected as the sire of m uch of the biochemical oxygen demand, mineralization of nutrients from organic matter, formation of toxic metabolites, and possibly the site of nutrient and organic matter recycling back into the pond food web. To determine the effect of sludge on water quality, nitrogen extincti on and shrimp production, three sludge management regimes were tested: (1) leaving sludge undisturbed in the pond (REMAIN); (2) removing slu dge accumulations at weekly intervals (REMOVE); and (3) resuspending o r moving sludge deposition daily to reduce the degree of anoxia (RESUS PEND). All ponds were operated without water exchange. Shrimp (Penaeus setiferus) growth was good, but survival ranged from om negligible in the REMAIN treatment to moderate in the REMOVE and RESUSPEND treatmen ts. The sludge management regime influenced overlying water qualify, w ith the most pronounced effect being a significant reduction in ammoni a-nitrogen, orthophosphate and in vivo fluorescence and an increase in dissolved oxygen for the REMOVE treatment. In the REMOVE treatment, 6 7% of nitrogen added as feed was harvested from the pond with sludge. Only 22% and 15% of the nitrogen added as feed was left in the pond sl udge at harvest for the REMAIN and RESUSPEND treatments respectively. All nitrogen inputs could be accounted for in the REMOVE treatment whi le 89% and 58% could be accounted for in the RESUSPEND and REMAIN trea tments respectively, indicating that the sludge management regime affe cted denitrification processes. If the sludge can be safely disposed o f on high land, pond water quality, as well as the quality of the wate r being returned to receiving streams in drain harvesting, is improved . Shrimp pond sludge can be used to improve terrestrial crop yields on well-drained but impoverished, soils. Shrimp production as high as 34 74 kg/ha without water exchange has not been reported elsewhere.