Study on some potentially suitable factors to prevent and reduce the mass mortality of sea bass Lates calcarifer: Technical paper No. 8/1992
1992
Niwes Ruangpanit | Janejit Kongkumnerd (National Institute of Coastal Aquaculture, Songkhla (Thailand))
Seabass hatcheries have suffered great losses due to the occurrence of a condition that renders the larvae weak and feeble at the age of 15-22 days. This condition, in which the larvae are slender, refusing food and floating at the water surface, causes mass mortality within 3-4 days. An experiment to test some potentially suitable factors to prevent and reduce the mass mortality was divided into 3 treatments. The first treatment consisted of the application of oxytetracycline (5 ppm) and malachite green (0.05 ppm) to the water, every 5 days to control the spread of bacteria and protozoa. The second was enriching the nauplii of the brine shrimp with fatty acids by feeding them codliver oil at least six hours, before they were fed to the larvae. In the third treatment the water temperature was elevated to 34-35 deg C for 5 days. Finally the treatment with the best results was selected and applied to nurse the seabass larvae in actual rearing nursing tanks to confirm its success. The experiment demonstrated that the elevation of water temperature to 34-35 deg C gave the best results and that it can prevent and reduce the feeble condition and thus the mass mortality of the larvae at this stage. The survival of the fish was 47.0 percent while the other methods showed a survival of only 0 and 4 percent. When the elevation of temperature was applied to the nursing tanks for confirmation it showed similar results to the laboratory experiments. The survival of the fish was 48.5 and 66.45 percent while the ones nursed at the normal temperature showed a poor survival of 0 and 11.39 percent.
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