Prevalence of the Parasitic Bopyrid Isopod Gyge ovalis (Shiino, 1939) in the Mud Shrimp Upogebia major (de Haan) in Jugyo Tidal Flat on the West Coast of Korea

초록

Many bopyrid isopods are parasites of thalassinidean shrimps, and they often attach to the gill chamber under the host’s carapace. Infestation by these bopyrid parasites commonly results in behavioral changes in their shrimp hosts, as well as reduced or eliminated reproduction by means of castration and/or feminization of males. We report here the prevalence of the parasitic bopyrid isopod Gyge ovalis (Shiino, 1939) in the mud shrimp Upogebia major (de Haan) in Jugyo Tidal Flat on the west coast of Korea.Mud shrimps were collected from February 2012 to July 2014 from Jugyo Tidal Flat (36°21'59.94"N,126°31'11.74"E) near the mouth of the Daecheon River, Boryeong, Chungcheongnam-do, Korea. A total of 3,808 shrimps were collected during the study period, among which 42.5% (1,619 shrimps) were infected by parasitic bopyrid isopods. Three bopyrid isopods (Gyge ovalis, Procepon liuruiyui, Orthione griffenis) were found in the branchial chambers of the mud shrimp, and the most prevalent bopyrid was Gyge ovalis, with 1,567 individuals (96.8%). The average infection rate (±SD) over the duration of the study period was 46.5% (±19.9), with the highest value of 89.7% occurring in July 2012 and the lowest of 22.7% in November 2013. Infection was more prevalent in summer at 79.4% (±7.5), but was much lower during other seasons, when it was 38.5% (±9.9). Frequency of infestation was not significantly different between males and females, as well as between the right and the left branchial chambers of the host shrimp. The carapace length of infested shrimps ranged from 12.30mm to 29.97mm (mean: 22.39±2.13mm), while noninfested shrimps were relatively larger, ranging from 12.97mm to 38.21mm (mean: 26.91±3.59mm). It should be noted that ovigerous females were not infested and were significantly larger, with a size range of 24.05mm to 34.29mm (mean: 28.42±1.80mm).