1Fisheries Research Agency (FRA), National Research Institute of Fisheries and Environment of Inland Sea, Stock Enhancement Division, Stock Enhancement Technology Section, Hakatajima Station, Imabari, Ehime 794-2305, 2Miyako Station, National Center for Stock Enhancement, FRA, Miyako,Iwate 027-0097, 3National Research Institute of Aquaculture, FRA, Aquatic Animal Health Division, Hatchery Health Research Group, Kamiura Station, Saiki, Oita 879-2602, Japan
Effects of ozone produced residual oxidants and povidone-iodine on hatching rates of Japanese flounder eggs were examined. The morula stage eggs collected both in May and June during the spawning period were exposed to ozonized seawater including oxidants (total residual oxidants: TROs) at concentrations ranging from 0.1 to 1.0 mg/L for a period from 1 to 15 min.
They were also exposed to seawater including povidone-iodine at concentrations ranging from 25 to 75 mg/L as available concentration of iodine (ACI) for the same period as the ozonized seawater. The hatching rate of eggs collected in May was nearly identical with that of the control eggs (p<0.05) when tested eggs were exposed to oxidants of less than 1.0 mg/L for 2 min, or to iodine of less than 75 mg/L of ACI for 15 min. On the other hand, the hatching rate of eggs collected in June was lower than that of eggs collected in May under the same test conditions. These results suggest that safe hatching conditions are influenced by the spawning phase. Safe treatment conditions for Japanese flounder eggs are TROs of 0.5 mg/L for 5 min and ACI of 50 mg/L for 15 min.