Adaptability of Moina affinis (Crustacea: Cladocera: Moinidae) to seawater salinity
近亲裸腹溞对海水盐度的适应性

By the methods of experimental ecology, this paper studied the effects of different salinity (0, 1, 2, 3, 4, 5) on the survival, growth, and reproduction of Moina affinis (Crustacea: Cladocera: Moinidae) at 25 degrees C +/- 0.5 degrees C under laboratory conditions, aimed to know the adaptability of freshwater cladocerans to seawater salinity. The results indicated that when the salinity increased from 0 to 5, the mean lifespan of M. affinis was 16.8 +/- 1.3, 17.8 +/- 3.5, 14.2 +/- 5.7, 13.0 +/- 1.6, 9.6 +/- 1.5 and 6.6 +/- 1.8 days, intrinsic increase rate (rm) was 0.91 +/- 0.01, 0.96 +/- 0.01, 0.86 +/- 0.10, 0.86 +/- 0.05, 0.49 +/- 0.18 and 0.24 +/- 0.06 d (-1) mean eggs production per clutch was 34.5 +/- 3.7, 34.2 +/- 3.9, 27.5 +/- 7.1, 34.6 +/- 3.9, 12.3 +/- 5.0 and 9.1 +/- 2.1 ind., and life fecundity was 410 +/- 32, 445 +/- 84, 250 +/- 106, 294 +/- 47, 59 +/- 38 and 24 +/- 6 ind., respectively. There was a significant difference in mean lifespan, intrinsic increase rate, and mean eggs production per clutch between treatments salinity 0, 1, 2 and 3 and treatments salinity 4 and 5, and in life fecundity between treatments salinity 0 and 1 and treatments salinity 2, 3, 4 and 5. The body length and daily growth rate was lower in control than in other treatments. It was suggested that salinity 5 was the maximum threshold salinity for the survival and reproduction of M. affinis, but after a short period of acclimatization in diluted seawater, the maximum threshold could reach 6. 5.