Bioacoustics of Tachaea spongillicola

Remarks Tachaea spongillicola can be distinguished from its congeners by the cephalon slightly immersed in pereonite 1, pleonite 4 with posterolateral margins extending beyond pleonite 5, incisor of the mandible with two cusps; the apical lobe of the maxilla without seta; inferior distal margin of carpus of pereopods 1–3 extended to propodus, pereonite 1 is as long as pereonite 2. Tachaea spongillicola and T. koreaensis (Song and Min, 2018) have similar body proportions, the body being 2.3 times longer than its greatest width, cephalon with broadly rounded rostrum,posterolateral margins of pleonite 4 extending beyond posterior margin of pleonite 5, pleonite 5 slightly posteriorly produced with posterolateral angles rounded. Tachaea spongillicola differs from T. koreaensis in the following characters: the pereonite 1 is as long as pereonites 2–7, the incisor of the mandible with two cusps, the apical lobe of the maxilla without seta, and the posterior margin of the pleotelson with nine robust setae. In contrast with T.koreaensis , the incisor of the mandible with one cusp,the apical lobe of the maxilla with one seta, and the posterior margin of the pleotelson with 10 robust setae. Among them, the present species is most closely related to T. tonlesapensis Nunomura, 2006 reported from the freshwater area of lake Tonlé Sap Cambodia , but the former is separated from the latter by the following features: (1) narrower pleotelson, (2) longer stylus of male second pleopod, (3) absence of wide vibratory lamella of maxilliped in both sexes,(4) numerous flagellar segments of both antennae, (5) smaller eyes and (6) numerous segments of the mandibular palp. Stebbing (1907) noted in T. spongillicola that the pleotelson is broadly rounded in females but is apically truncate in males. Based on this information Stebbing (1907) synonymised Tachaea incerta Hansen, 1890 with T. crassipes Schioedte and Meinert. Stebbing (1907) distinguished T. spongillicola from T. crassipes by the apical article of the maxillipeds as well as the decreased setations of the pereopods and the shorter pleon (relative to pereion length) in the former species. Occurrence of Tachaea spongillicola A total of 40 P. silasi available in the cages were examined for the isopod infestation; 35 were infested with 186 T. spongillicola , corresponding to an overall prevalence and intensity of 87.5% and 5.31, respectively. Among the total of 126 T. spongillicola collected, 74 were non-ovigerous females and 52 were males. Gross features on the infected fish showed lesions on various parts of the body. The isopod attached at the base of the fins, head and abdomen, and to the gill cavity; we noted also that it was attached to weak and dead fishes only. In severe case, haemorrhages were seen all over the body of the infected fish, leading to its death ( Figure 6 ). The isopod sucked the fish’s blood and it may have detached when its stomach was full.