HATCHING OF RESTING EGGS PRODUCED BY BRACHIONUS CALYCIFLORUS CULTURED UNDER DIFFERENT CONDITIONS
XI Yi\|Long HUANG Xiang\|Fei (Institute of Hydrobiology, The Chinese Academy of Sciences, Wuhan?430072, China)
In order to identify the optimal condition of resting egg formation, or to increase the hatching rate of resting eggs produced by freshwater rotifer Brachionus calyciflorus under certain culture conditions, we experiments were made to examined the hatching of resting eggs produced by B. calyciflorus cultured under different temperatures, alga diets, illumination periods and pHs, respectively. The results showed that the hatching duration of resting eggs under different conditions in which resting eggs were produced and hatched was the initial seven days of the experiment, and the hatching rate peak occurred during the initial three days. There were highly significant effects of temperatures at which resting eggs was produced and hatched independently and in interaction on the accumulative hatching rate of resting eggs. The accumulative hatching rate of resting eggs which was produced and hatched at 20℃ was 52.50±6.89%, and the highest among all the tested experimental combinations. Both the rotifer's feeding history and hatching temperature influenced very significantly on the accumulative hatching rate of resting eggs, respectively. The mean value of accumulative hatching rate of resting eggs produced by B. calyciflorus which fed on Chlorella pyrenoidosa was 27.92%, and higher than that on Scenedesmus obliquus or mixed algae composed of C. Pyrenoidosa and S. obliquus, which was 12.29% and 18.75%, respectively. There were no significant effects of the illumination conditions in which resting eggs were produced and hatched on the accumulative hatching rate. The pHs at which resting eggs were produced influenced very significantly on the accumulative hatching rate of resting eggs. The accumulative hatching rate of resting eggs formed at pH6.5 and pH7.5 were 32.50±7.07% and 38.75±15.53%, respectively, and both of them were higher than that at pH8.5～10.5. From the above stated and our other published results, one can state that all the hatching pattern of resting eggs produced and hatched under different conditions are synchronous. 20℃ and pH7.5 are the optimal temperature and pH value for resting egg formation of B. calyciflorus, respectively.