Occurrence of Alien Freshwater Crayfish (Decapoda: Astacidea) in Taiwan: A Review

Abstract This study reviews the introduction history and distribution of alien freshwater crayfish in Taiwan through literature surveys, morphological examination of preserved specimens, and field surveys. Since the 1970s, multiple non-native crayfish species have been introduced mainly for ornamental, culinary, and aquaculture purposes, but their status has been poorly documented. The introduction of alien freshwater decapods began in 1970 with large freshwater prawns (Macrobrachium spp.). In the 1980s, the red swamp crayfish, Procambarus clarkii, was introduced and established in the wild. The 1990s saw introductions of the Australian redclaw, Cherax quadricarinatus, and yabby, Cherax destructor, for aquaculture trials. Morphological observations of wild P. clarkii specimens and absence of branchiobdellidan ectosymbionts—typical in Japanese populations—suggest a possible Japanese origin, though alternative explanations exist, warranting genetic confirmation. Field surveys revealed an established population of C. quadricarinatus in the Mudan River system, likely due to escapes from aquaculture and pet releases. Research on alien crayfish in Taiwan is developing, with increasing graduate level studies. This review clarifies their introduction history and distribution, providing fundamental data for fisheries management and invasive species control.