Abstract: The morphological characteristics and distribution of water fleas Scapholeberiskingi Sars and the effects of salinity on its survival, growth and reproduction at constant temperature (25±1) ℃ were investigated by field and experimental ecological methods in order to clarify the salinity adaptability of the animal. The synchronous<24 h old water fleas with body length of (28.5±1.5)μm was held in a 20 mL glass test tube at a density of 10 individuals per tube and exposed to a salinity of 0 (control group), 1.0, 2.0, 3.0, 4.0, 5.0, and 6.0 for 24 h and 48 h to evaluate the acute salinity adaptability of the water fleas. The same size water fleas was reared in a 20 ml glass test tube at a density of 1 individual per tube at a salinity of 0 (control group), 0.5, 1.0, 1.5, and 2.0, and daily survival, first-brood time, and first-brood fecundity were recorded during the experiment and body length were measured in 2, 4, 6, 10, and 14 d to probe into the chronic salinity adaptability of the water fleas. The results showed that the water fleas was widely distributed in freshwater rivers, ponds, lakes and reservoirs. The acute toxicity test showed that the half lethal concentration (LC50) of salinity to the water fleas was 3.35 in 24 h and 2.27 in 48 h, with safe concentration of 0.31. The chronic toxicity test showed that the water fleas had significantly higher survival rate and life span in 0.5 salinity group than those in 1.5 and 2.0 salinity groups did (P<0.05). The maximal growth rate of body length was observed in salinity 1.5 group, significantly higher in 1.0 and 1.5 salinity groups than that in the control group and the 0.5 salinity group (P<0.05). There was the maximal first-brood fecundity in the 1.0 salinity group, significantly higher than that in the 2.0 salinity group (P<0.05). The maximal total neonate was found in the 1.0 salinity group, significantly higher in the control group, 0.5 group and 1.0 salinity group than that in 1.5 and 2.0 salinity groups (P<0.05). The net productive rate, intrinic rate of increase, finite rate of increase and mean generation time were higher in 0.5 and 1.0 salinity groups, higher than or close to the control group (P>0.05), and lower population growth parameters in the 1.5 and 2.0 salinity groups. The findings indicated that the water fleas had very low tolerance to salinity, and that the growth and reproduction of the water fleas was promoted by increasing salinity properly (0.5-1.0). The water fleas could be used as a test organism to indicate and monitor seawater erosion, fresh water pollution and salinization due to its high sensitivity to salinity.
2021, Vol. 36 
