THE EFFECTS OF TEMPERATURE ON EGG LAYING, EGG HATCHING AND LARVAL DEVELOPMENT OF DACTYLOGYRUS VASTATOR

The effects of water temperature on egg laying and hatching in vitro were investigated, and egg laying and development in vivo at 20℃ were also characterised. The results indicated a positive correlation between mean egg production and temperature in vitro, and the mean egg production was 5.9, 9.1, 9.2 and 13.4 eggs/worm at 10, 20, 30 and 35℃, respectively. Except 4℃, majority of the eggs were laid during the first 5h. However, egg laying of the mature worms was continuous and uniform, with a mean 6.5 eggs/worm at 20℃ per day. Although the hatching time and the duration of hatching declined with increasing temperature, with 19d, 3d, 2d, 36h and 24d, 5d, 5d, 3d at 10℃, 20℃, 30℃ and 35℃, respectively, the highest hatching success was observed at 30℃. Ninety percent of worms reached maturity within 7 days post-infection when exposed to 20℃. The life-cycle of D. vastator from egg to sexual maturity lasted for 8 to 11 days which indicated that a second treatment should be administered a week later at 20℃.