Habitat utilization and seasonal occurrence of <i>Tachaea chinensis</i> (Isopoda: Corallanidae) infesting freshwater shrimps in Lake Biwa, central Japan

Abstract

Monthly quadrat sampling of freshwater shrimps infested by the corallanid isopod Tachaea chinensis was conducted in Lake Biwa, central Japan, between April 2014 and September 2015. In total, 3,222 shrimps, including 2,786 Neocaridina spp., 309 Paratya improvisa, and 127 Palaemon paucidens were collected. Individuals of 431 T. chinensis were found from those hosts. The prevalence was 12.2% in Neocaridina spp., 5.5% in P. improvisa, and 24.4% in P. paucidens, respectively. All isopods found on hosts were immature stages and showed an annual emergence pattern; newly hatched juveniles were first sampled in August, increased the body length until May, and were not observed in June-July. To collect T. chinensis apart from the hosts, a cage trap filled with reed roots was put on the study site between June 2014 and September 2015. Isopods were collected in July and September. Specimens trapped in 2015 consisted of adult or premature individuals, and 39 out of 46 adult females collected were ovigerous. During an observation using snorkeling in July 2014, 29 adults were observed under stones and in withered Phragmites australis roots. Thus, T. chinensis reproduces in benthic habitats during summer. Subsequently, juveniles appear and grow via a series of molts on the hosts until the following year.

Host selection and potential predation in the host-parasite interaction between the isopod Tachaea chinensis and freshwater host species

“…Therefore, T. chinensis isopod may demonstrate a high degree of flexibility with regard to host species and readily adapt to different hosts that provide adequate space for attachment. Previous studies from China and Japan have also come to similar conclusions ( Ota, 2019 ; Xu et al, 2019 ).…”

“…In one study, individuals of T. chinensis were always found on host shrimps that are slightly larger in carapace length compared to its own body length ( Khalfan et al, 2022 ). Similar findings were observed by Ota (2019) , who concluded that the small-sized shrimp, Neocaridina spp., may not offer adequate space for the isopod to safely attach itself. Khalfan et al (2023) , using behavioral experiments, further elucidated this hypothesis and concluded that 0.7–1.0 ratios of parasite body length to host shrimp carapace length appeared to be preferred by the isopod T. chinensis , because it provides adequate space for safe attachment while avoiding potential consumption by the available host shrimps.…”

“…Isopod prevalence may be partially governed by the locality and type of species found at a given location ( Nagasawa et al, 2018 ; Ota, 2019 ; Xu et al, 2019 ), which might explain the great variability in the selected host species in the single-host treatments. Therefore, T. chinensis isopod may demonstrate a high degree of flexibility with regard to host species and readily adapt to different hosts that provide adequate space for attachment.…”

“…Tachaea chinensis Thielemann, 1910 is an ectoparasitic isopod infesting freshwater shrimps and prawns in Japan, China, Vietnam, Thailand, and Malaysia ( Shiino, 1965 ; Nagasawa et al, 2018 ; Xu et al, 2019 , 2021 ; Nunomura and Shimomura, 2020 ). It exhibits a biphasic lifestyle– isopods in the manca stage and immature stage infest the host shrimps, whereas during the mature stages, they detach for reproductive proposes ( Ota, 2019 ). The manca stage passes through five distinct embryonic stages within 30–38 days, although the period from the manca stage to the mature adult stage may span 180 days on average ( Xu et al, 2021 ).…”

“…Parasites-host specialization differs by geographical locations, whereby host density may play an important role in the observed infestation pattern ( Ota, 2019 ). In Japan, the isopod T. chinensis is found on various host species depending on the density of the host species at a given site, but they are frequently observed infesting the shrimp Palaemon paucidens De Hann, 1844, in the Honshu region in Japan's mainland ( Nagasawa et al, 2018 ).…”