| Summary: | 碩士 === 國立海洋大學 === 水產養殖學系 === 88 === The hatch of eggs and survival of larvae for grouper Epinephelus coioides always influenced by bacteria and virus. The performance of larvae culture was poor. In order to improve these problems, we have used several methods to remove the microorganism and organic matter in culturing water. At first, the eggs were disinfected by ozonation water with ozone concentrations (expressed as total residual oxidant, TRO) of 0.1 — 0.5 mg/L and for 1 min. After disinfection, these eggs were put into hatchery tank. The results showed that the hatch rates were above 95 % if the TRO concentrations were below 0.4 mg/L. In contrast, the hatch rate was 29 % only, if the egg was disinfected with 0.5 mg TRO/L. This suggested that 0.5 mg TRO/L was toxic to egg and 0.4 mg/L was decrease the survival rate. Thus the concentration of TRO for disinfection of egg should be below 0.2 — 0.3 mg/L.
In another experiment, eggs were put in a continuous upflow tank. The eggs in tank were washed and hatched with water treated by two methods. One is treated with ozone and then the TRO is removed by activated carbon (OD), another is treated with cartridge filter and UV disinfector (FU). The results of four test runs indicated that the OD group had a better hatch rates (88.4, 70.1, 84.7 and 67.0 %) than FU group, but the survival rate of larvae after hatched had no different between these two groups.
After hatch, the larvae were put in several beakers which contain water treated with various disinfecting method and removal methods for oxidant products. The results showed that the water disinfected by ozone and removed TRO by sodium thiosulfate would be toxic to larvae. But the OD water and water treated with other method had the same survival rate of larvae.
In conclusion, the E. coioides grouper eggs disinfected with 0.2 — 0.3 mg TRO/L of ozone have a high hatch rate and after hatched the larvae have a high survival rate also. In another way, the grouper egg could be washed and hatched in a continuous flow hatch tank by using OD treated water to get a high hatch rate and survival of larvae. In larviculture, the OD treated water and with no aeration in culture tank during the yolk sac stage would be the better choice.
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