FISHERIES RESEARCH INSTITUTE,MOA,TAIWAN

Several experiments were conducted to assess the feasibility of culturing Australian crayfish species in Taiwan and to evaluate its impact on the environment. In the temperature trial, the result indicated that the low lethal temperature of Yabbie Cherax destructor was lower than Redclaw Cherax quadricarinatus (4.5℃ vs. 5.7℃), and the high lethal temperature is almost similar in both species (40.3℃ and. 40.6℃). The result of lethal oxygen trial showed that crayfish survived in lower ambient oxygen concentration than fish, and their lethal oxygen levels were 0.7 and 0.9 ppm for Yabbie and Redclaw, respectively. In the experiment on their impact on rice field, both crayfish did not destroy the rice seedlings unless there was no food (i. e. duckweed or artificial feed) available. Yabbie cut down the seedlings in the field 3 days after stocking at food shortage. The seedlings were wiped out ten days after stocking. The relative strengths of practical chemotherapeutic agents on crayfish were in the following order: trichlorphone, BKC, malachite green, KMnO4, CuSO4‧5H2O, methylene blue, teaseed cake, formalin and sea salt. In the trial of toxicities of selected herbicide to crayfish, the result showed that paraquat was more toxic than nienchun. In the growth trial for Yabbie, higer storking density (100 Yabbie/pond) resulted in slower growth rate. Furthermore, providing plastic pipes as shelter remarkably increased the survival rate of Yabbie. Planting water hyacinth Eichornia crassipes as shelter also improved the survival rate but the effect was not as good as the plastic pipes.
Key words: Crayfish, Adaptation, Rice field, Dissolved oxygen, Shelter