Life cycle of the ectoparasite Tachaea chinensis (Isopoda: Corallanidae) on the freshwater shrimp Palaemonetes sinensis (Decapoda: Palaemonidae)

In this study, we describe in detail the life cycle of Tachaea chinensis (Isopoda: Corallanidae), a branchial ectoparasitic isopod that infests the freshwater shrimp Palaemonetes sinensis in China. We obtained 14 ovigerous T. chinensis females (8.22-11.92 mm in length) and observed the development of embryos through 5 sequential ontogenetic stages within the brood pouches (marsupium) of these females. The number of eggs or mancae (post-larval juveniles) held in the female marsupium ranged from 31 to 86, with a mean +/- SD of 61.25 +/- 16.16 eggs. Female T. chinensis were semelparous, i.e. individuals died following the release of mancae from the marsupium. Released mancae were non-planktonic and immediately infective to host shrimps. However, only a few mancae successfully established contact with a host, and it is thus assumed that the remainder were predated by shrimp. Attached T. chinensis fed on the host hemolymph, and subsequent to host death, these isopods typically searched for a new host. We also found that T. chinensis exhibits a host preference: most mancae attached to P. sinensis rather than to Neocaridina sp. or Macrobrachium nipponense. This study provides valuable empirical data that will support future research on the prevention and control of parasitic isopod infections.