[Characteristics in life history of Brachionus forcatus and B. caudatus: a comparative study].

By the method of individual culture and with 3.0 x 10(6) cells ml(-1) of Scenedesmus obliquus as the food, a comparative study was made on the characteristics in life history of Brachionus forcatus and B. caudatus at 18 degrees C, 23 degrees C, 28 degrees C and 33 degrees C. The results showed that at 18 degrees C and 23 degrees C, both the reproductive stage and the mean lifespan of B. caudatus were longer than those of B. forcatus, and the number of eggs produced by B. caudatus in its whole life was larger than that by B. forcatus. At 28 degrees C , there were no significant differences between B. forcatus and B. caudatus in the durations of their main development stages, mean lifespan, and the number of eggs produced. At 33 degrees C, the reproductive and post-reproductive stages and the mean lifespan of B. forcatus were longer than those of B. caudatus, and the number of eggs produced by B. forcatus in its whole life was larger than that by B. caudatus. At 18 degrees C, the life expectancy at hatching, net reproductive rate, and intrinsic rate of population increase were all larger for B. caudatus than for B. forcatus; but at 23 degrees C and 28 degrees C, only the life expectancy at hatching was larger for B. caudatus than for B. forcatus. When the temperature reached 33 degrees C, the generation time, life expectancy at hatching, net reproductive rate, and intrinsic rate of population increase were all larger for B. forcatus than for B. caudatus. There also existed differences between B. forcatus and B. caudatus in the responses of the durations of their main development stages, mean lifespan, number of eggs produced in whole life, generation time, life expectancy at hatching, net reproductive rate, and intrinsic rate of population increase to increasing temperature. B. caudatus was more adaptable to lower temperature, while B. forcatus was in adverse.