Effects of salinity and used medium on the induction of sexual reproduction in the rotifer Brachionus rotundiformis

Abstract

This study examined the effect of salinity and medium used on the induction of sexual reproduction for the mass production of the resting eggs in the marine rotifer Brachionus rotundiformis for 9 days. After exposure to various salinities, the mixis rate in all treatments began to increase on the third day and decreased after the 4th or 5th day. The resting eggs appeared on the 4th day at 10‰, 15‰, 20‰, 25‰. In particular, the fertilization rates with 33.3% and 31.3% at 20‰, 25‰ on day 6 were higher than those of the others, respectively. Mean mixis rate for 9 day at 0‰ and 20‰ were the highest with 25.3% and 20.2%, respectively, and the fertilization rate (14.0%) at 25‰ was the highest. In the used medium experiment, the mixis rate in all treatments were similar to the results of the salinity experiment. The resting eggs were only found at 0% and 25% used medium treatments. While there were no significant difference in mean fertilization rate of all treatments, mean mixis rate (22.3%) in 25% treatment was higher than that of the control (0% treatment). As a result, salt stress was more effective than using used medium to induce the sexual reproduction in B. rotundiformis. The optimum salinity was considered to be 20-25‰ which caused a high mixis and fertilization rate in the rotifer. These results provide basic data for the mass production of the rotifer resting eggs.the mixis rate in all treatments began to increase on the third day and decreased after the 4th or 5th day. The resting eggs appeared on the 4th day at 10‰, 15‰, 20‰, 25‰. In particular, the fertilization rates with 33.3% and 31.3% at 20‰, 25‰ on day 6 were higher than those of the others, respectively. Mean mixis rate for 9 day at 0‰ and 20‰ were the highest with 25.3% and 20.2%, respectively, and the fertilization rate (14.0%) at 25‰ was the highest. In the used medium experiment, the mixis rate in all treatments were similar to the results of the salinity experiment. The resting eggs were only found at 0% and 25% used medium treatments. While there were no significant difference in mean fertilization rate of all treatments, mean mixis rate (22.3%) in 25% treatment was higher than that of the control (0% treatment). As a result, salt stress was more effective than using used medium to induce the sexual reproduction in B. rotundiformis. The optimum salinity was considered to be 20-25‰ which caused a high mixis and fertilization rate in the rotifer. These results provide basic data for the mass production of the rotifer resting eggs.