Seawater treatment for larval culture of the fish Sciaenops ocellatus Linnaeus (red drum)

Poor survival of marine fish larvae during the first days of culture has frequently been observed. The possibility that microbes present in the incoming seawater might contribute to this mortality led to the development of a seawater treatment protocol for hatcheries. Several combinations of filtration at different particle sizes, and chlorination at different levels were tested with red drum larvae. The highest mortality in all experiments was found in untreated or 1 mu m filtered seawater. A significant and consistent improvement in larval survival over control treatments resulted from filtering seawater through 1 mu m filter, followed by chlorination at 5 ppm Cl- for 2 h, and dechlorination with sodium thiosulfate accompanied by strong aeration for a period of 1 h. Bacteria counts were drastically reduced by this treatment; however, bacteria numbers were similar or even higher 24 h after treatment than in untreated seawater. Therefore, it is postulated that it is not bacteria numbers, but the species composition of the microbiota that affects larval survival. (C) 1999 Elsevier Science B.V. All rights reserved.