DEVELOPMENT AND GROWTH OF DIAPHANOSOMA BRACHYURUM LIEVEN(1848) (CLADOCERA: SIDIDAE)

Diaphanosoma brachyurum is considered to be the dominant cladoceran from June to September in Lake Donghu. Its development and growth were observed in laboratory under constant temperature.Duration of egg-embryonic development (D) was found to be shortened as the tem perature (T) increases. The regression equation may be expressed aslog D=2.0195-1.3784 log T (20—35℃)Growth rate varies with the number of instars. In general, the growth curves show an initial high rate in the juvenile instars, an intermediate rate in the young adult ins tars, and a low rate in the older adult instars.There are 4 juvenile instars followed by 10 adult instars at 25℃ whereas there are 3 juvenile instars followed by 11 to 12 adult instars at 30 or 35℃.Juveniles moult more frequently than adults. The mean duration of an adult instar was found to be twice as that of an juvenile instar, but almost the same as that of egg embryonie development. The duration of the instar stages and the total life span are in versely related to the temperature.The number of the cumulative eggs for each adult during the experiment was 65.63, 69.09, and 51.77 at 25, 30, 35℃, respectively.The rate of egg production was maximum (1.3421) at 25℃, medium (1.2856) at 30℃ and minimum (1.1488) at 35℃.Results of the present study are compared with those given by other authors and their differences are also discussed.