Impacts, control and perception of introduced Crayfish in Thailand.
To gain more scientific understanding regarding Crayfish in a tropical climate since its first introduction in 1987, this research focused on perceptions of non-native species trading and invasive species as it relates to management. Pet store owners and farmers were interviewed. There are two Crayfish species in Thailand - Procambarus clarkii and Cherax quadricarinatus and the Crayfish trade is expanding due to high demand. The results demonstrated that respondents had a basic knowledge of Crayfish biology, primarily related to farming production. However, most respondents lacked understanding of the negative impact and invasiveness of Crayfish and, therefore, the potential risk of invasion. Respondents suggested: (1) controlling invasive species by the government using stringent law enforcement and prohibition of the release of nonnative species into the wild and harsher legal penalties for those who do not comply with the law; and (2) an educational campaign, especially on the negative impacts of Crayfish, should be publicized targeting both traders and pet owners. We further examined Crayfish biology and behavior using a laboratory experiment. The study considered the impact of different densities of Crayfish in captivity on survival rates and tolerance of Crayfish to different environmental conditions. The potential effects of native freshwater species as control agents for Crayfish were also determined. Results revealed that stocking Crayfish at a high density tended to achieve higher growth and survival rates than at a low density, as Crayfish reared at a high density were unable to exhibit agonistic (fighting) behavior in a very confined area. It was also revealed that Crayfish are sensitive to polluted water conditions (dissolved oxygen 2.55±0.25 mg l-1; biological oxygen demand 8.45±0.04 mg l-1) and could not survive there very long. This intolerance limits the potential of Crayfish to spread further to other water bodies in Thailand. Biological control agents demonstrated that Anabus testudineus, or the Climbing Perch, appeared to be the most effective predator and may help resist invasion of exotic Crayfish in the wild.