Abstract
Trichodinids, which are ciliate protists, are causative agents of an aquatic animal disease, trichodiniasis, especially among both captive and wild fish. This disease can adversely affect aquaculture and have economic impacts. The objectives of this study were to evaluate the prevalence and mean intensity of Trichodina unionis infection, describe qualitative and quantitative morphological characters, and perform a molecular phylogenetic analysis. The gastropod samples were randomly collected by hand-picking and a hand net. Trichodina unionis was collected by the crushing method under a stereomicroscope. Among all 4977 examined gastropods, 55 individuals of two gastropod species, Gyraulus siamensis and Physella acuta, were found to be infected by T. unionis, with overall prevalence and mean intensity of infection of 1.11% and 16.65, respectively. The characteristics of the denticles indicated T. unionis as having moderately wide blades and moderately curved blade margins, with distinctive bend angles near the distal end. The quantitative characters showed some variations, which could be due to food availability. Molecular phylogenetic analysis conducted with 18S rRNA provided a monophyletic tree of our specimens and previously identified T. unionis, confirming species identification. This study represents the first record of T. unionis in Thailand.
Highlights
Trichodina, a genus of ciliate protists, belongs to the family Trichodinidae and is well known as the causative agent of trichodiniasis in numerous aquatic animals, especially both cultured and wild fish [23,24,25, 38]
All 4977 individuals of the collected freshwater gastropods were examined for trichodinid infection, and 55 of the examined gastropods (belonging to two species, i.e., Gyraulus siamensis and Physella acuta (Fig. 3) were found to be infected with T. unionis
No trichodinids were found in 16 species of 8 families of freshwater gastropods (Table 2)
Summary
Trichodina, a genus of ciliate protists, belongs to the family Trichodinidae and is well known as the causative agent of trichodiniasis in numerous aquatic animals, especially both cultured and wild fish [23,24,25, 38]. In Thailand, Trichodina has been rarely reported, with a few studies showing the occurrence of this genus on the basis of morphological characteristics conducted in Nakhon Si Thammarat, Pattani and Trang provinces [21, 29, 33]. Worananthakij and Maneepitaksanti [39] addressed Trichodina at the species level, with three species found to be infecting red tilapia from Pathum Thani province, with identification based only on morphological characters
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