First report of freshwater atyid shrimp, Caridina formosae (Decapoda: Caridea) as a host of ectosymbiotic branchiobdellidan, Holtodrilus truncatus (Annelida, Citellata)

In recent years, ornamental shrimps gained increasing popularity in the aquarium trade. Unfortunately, they are potential vectors of epibionts, which may be unintentionally introduced to aquaria with imported shrimps. This contribution presents the first report of the occurrence of Holtodrilus truncatus on aquarium freshwater shrimp Caridina formosae . A total of 120 shrimp imported from Taiwan as aquarium pets were examined for the presence of epibionts. Holtodrilus truncatus occurred in 23.3% of shrimps. A total of 29.6% of crustaceans showed signs of damages as a result of H. truncatus activity. The shrimp is not common in the ornamental trade and is not subject to selective breeding. Therefore C. formosae populations available on the market, if not wild-caught, are most likely very similar to those occurring in Taiwanese natural water bodies, where H. truncatus occurs in Neocaridina shrimp. Neocaridina spp. are a known host for this epibiont, and transmission between species might occur in nature as well as in the aquarium trade were densities of animals are often high. The ability of H. truncatus to infect also highly invasive crayfish Procambarus clarkii , might also pose concern for regions where this crustacean is widespread. The actual lack of preventive measures for shrimp epibionts as well as confirmed releases of ornamental crustaceans into new aquatic ecosystems may result in further spread of H. truncatus , a potential new threat to native crustaceans and other epibionts.