EFFECT OF TEMPERATURE AND FOOD CONCENTRATION ON THE GROWTH AND REPRODUCTION OF SIMOCEPHALUS VETULUS

In this study, body length, duration of instar, lifespan, egg production, and survival rate of Simocephalus vetulus were investigated under three food concentrations and two temperatures(20℃and 25℃)in the laboratory.S. vetulus was from the coal collapsed water in Huaibei City. The collected animals were cultured in an incubator at 25 ℃.Females containing embryos were isolated in 50 mL beakers and acclimated to the experimental temperatures. The offspring from these females were isolated and reared under the same conditions until the juveniles were released. Then, these juveniles were used for the experiment. Three food concentrations(2×105, 1×105 and 1×104cellsm L-1) ofScenedesmus obliquus were used. The culture medium was tap water that was exposed, and was refreshed daily. All experiments were carried out under a constant light regime of 12 hlight: 12 h dark.The results showed: S. vetulus had four juvenile instars, except there were five at 20℃ and under low food concentration,and 10-13 adult instars. The adult instar durations of S.vetulus were higher than those of juvenile instars, and the development time of the first adult instar was generally the longest. The first pregnant time and each duration of instar shortened with the increase of food concentration at same temperature, while average body length and brood size showed a reverse trend. At 20℃,the highest lifespan under high and middle food level was longer than at low food level, while mean lifespan was shorter than at low food level. At 25℃, both mean and highest lifespan under high and middle food concentrations were longer than at low food concentration. Mean body length at late instars at 25℃ was longer than at 20℃ at same food levels, while duration of instar was shorter at 25℃ than at 20℃. The maximum of body length (2. 82mm) appeared the sixteen instar at 25℃ and high food concentration,and both the average largest egg production(144 ind.) and maximum of the intrinsic rate of population increase(0.41 ind. day-1) ofS. vetulus occurred at 25℃ and under high food level. The statistical analysis showed that the relationship between egg production and body length ofS. vetulus was positive significance. The threshold food concentration was4 cells mL-1(S. obliquus).The author also discussed the possibility whetherS. vetulus became a suitable species for mass culture at aquiculture.