THE EFFECT OF LOW-RATE SAND FILTRATION AND MODIFIED FEED MANAGEMENT ON EFFLUENT QUALITY, POND WATER-QUALITY AND PRODUCTION OF INTENSIVE SHRIMP PONDS

Pond water in intensive shrimp ponds is typically high in nutrients, s olids, and BOD and may have an adverse environmental impact when disch arged to natural waters. As part of ongoing research to develop intens ive production technologies that minimize the potential for environmen tal impact, a study investigated the effect of low-rate, coarse-grain sand filtration on the quality of effluent being discharged from an in tensive shrimp pond receiving 5% d(-1) water exchange. The effect of s and filtration on a recirculating no-exchange pond tvas also examined. For comparison, a third pond received no water exchange and no filtra tion. Sand filtration removed some particulate matter, but levels of d issolved and particulate organic and inorganic nutrients were changed little and were sometimes higher as the result of in situ decompositio n. Low-rate sand filtration is not seen as a cost-effective method of increasing the carrying capacity of no-exchange shrimp ponds or drasti cally improving the effluent quality of ponds with water exchange. Com pared to previous studies with decreased or no water exchange, the app lication of feed in these ponds was more stable with small portions fe d at frequent intervals with a constant rate of 80 kg ha(-1) d(-1). Th ese ponds, stocked with 40 m(-2) juvenile Penaeus vannamei, had excell ent survival and normal growth, resulting in production levels approac hing 7,000 kg ha(-1) crop(-1) without water exchange. This indicates t hat intensive shrimp farming may be possible in static no-exchange sys tems, thereby minimizing the potential impact of effluent as long as f eed inputs do not overwhelm the assimilative capacity of the pond ecos ystem.