New data of two trichodinid ectoparasites (Ciliophora: Trichodinidae) from farmed freshwater fishes in Hubei, China

Fish ectoparasite detection, collection and curation

Fish parasitology is a dynamic and internationally important discipline with numerous biological, ecological and practical applications. We reviewed optimal fish and parasite sampling methods for key ectoparasite phyla (i.e. Ciliophora, Platyhelminthes, Annelida and Arthropoda) as well as recent advances in molecular detection of ectoparasites in aquatic environments. Ideally, fish capture and anaesthesia as well as parasite recovery methods should be validated to eliminate potential sampling bias and inaccuracy in determining ectoparasite population parameters. There are considerable advantages to working with fresh samples and live parasites, when combined with appropriate fixation methods, as sampling using dead or decaying materials can lead to rapid decomposition of soft-bodied parasites and subsequent challenges for identification. Sampling methods differ between target phyla, and sometimes genera, with optimum techniques largely associated with identification of parasite microhabitat and the method of attachment. International advances in fish parasitology can be achieved through the accession of whole specimens and/or molecular voucher specimens (i.e. hologenophores) in curated collections for further study. This approach is now critical for data quality because of the increased application of environmental DNA (eDNA) for the detection and surveillance of parasites in aquatic environments where the whole organism may be unavailable. Optimal fish parasite sampling methods are emphasised to aid repeatability and reliability of parasitological studies that require accurate biodiversity and impact assessments, as well as precise surveillance and diagnostics.

High prevalence and mean intensity of trichodinids and monogeneans on Nile tilapia (Oreochromis niloticus) in Indonesian hatcheries

This study describes recent infestations of ectoparasites on tilapia fingerlings in several hatcheries. High mortality of fingerlings and juvenile fish often occurs in hatcheries but the causative agents remain unclear. Nile tilapia fingerlings were obtained from three hatcheries in South Sulawesi, Indonesia. The fish were euthanized in clove oil, length and weight were measured, and the whole body and gills were examined for ectoparasites. Trichodinids were silver stained with 2% AgNO3, whereas monogeneans were placed in glycerin-alcohol and examined under a microscope. Other protozoans were placed directly on fresh mounts and identified under a compound microscope. The monogenean parasites were cleaned and placed in a microtube containing 70% alcohol for molecular identification. Trichodinid (Trichodina centrostrigeata, T. magna, Paratrichodina africana, Trichodinella sp., and Tripartiella sp.), and monogenean (Gyrodactylus sp. and Cichlidogyrus spp.) parasites were found in highly prevalent. The Cichlidogyrus specimens were morphologically identified as C. sclerosus, C. halli, and C. thurston, but only C. sclerosus and C. halli were confirmed based on partial 28S rRNA. The Gyrodactylus specimens were morphologically identified as G. cichlidarum and confirmed based on the ITS region. This is the first time that T. centrostrigeata and P. africana have been confirmed on fish from hatcheries and is also the first time that C. sclerosus, C. halli, and G. cichlidarum have been verified in Indonesian hatcheries based on a molecular technique. The high infestation rates of these parasites were likely caused by rearing the fish under stressful conditions, indicating low biosecurity and poor health management practices in the aquaculture facilities.

Effect of Copper Sulphate Exposure on the Oxidative Stress, Gill Transcriptome and External Microbiota of Yellow Catfish, Pelteobagrus fulvidraco

This study aimed to investigate the potential adverse effects of the practical application of copper sulfate on yellow catfish (Pelteobagrus fulvidraco) and to provide insights into the gill toxicity induced by copper sulphate. Yellow catfish were exposed to a conventional anthelmintic concentration of copper sulphate (0.7 mg/L) for seven days. Oxidative stress biomarkers, transcriptome, and external microbiota of gills were examined using enzymatic assays, RNA-sequencing, and 16S rDNA analysis, respectively. Copper sulphate exposure led to oxidative stress and immunosuppression in the gills, with increased levels of oxidative stress biomarkers and altered expression of immune-related differentially expressed genes (DEGs), such as IL-1β, IL4Rα, and CCL24. Key pathways involved in the response included cytokine-cytokine receptor interaction, NOD-like receptor signaling pathway, and Toll-like receptor signaling pathway. The 16S rDNA analysis revealed copper sulphate altered the diversity and composition of gill microbiota, as evidenced by a significant decrease in the abundance of Bacteroidotas and Bdellovibrionota and a significant increase in the abundance of Proteobacteria. Notably, a substantial 8.5-fold increase in the abundance of Plesiomonas was also observed at the genus level. Our findings demonstrated that copper sulphate induced oxidative stress, immunosuppression, and gill microflora dysbiosis in yellow catfish. These findings highlight the need for sustainable management practices and alternative therapeutic strategies in the aquaculture industry to mitigate the adverse effects of copper sulphate on fish and other aquatic organisms.

Threats to UK freshwaters under climate change: Commonly traded aquatic ornamental species and their potential pathogens and parasites

The aquatic ornamental industry, whilst providing socio-economic benefits, is a known introduction pathway for non-native species, which if invasive, can cause direct impacts to native species and ecosystems and also drive disease emergence by extending the geographic range of associated parasites and pathogens and by facilitating host-switching, spillover and spill-back. Although current UK temperatures are typically below those necessary for the survival and establishment of commonly-traded tropical, and some sub-tropical, non-native ornamental species, the higher water temperatures predicted under climate-change scenarios are likely to increase the probability of survival and establishment. Our study aimed primarily to identify which of the commonly-traded non-native ornamental aquatic species (fish and invertebrates), and their pathogens and parasites, are likely to benefit in terms of survival and establishment in UK waters under predicted future climate conditions. Out of 233 ornamental species identified as traded in the UK, 24 were screened, via literature search, for potential parasites and pathogens (PPPs) due to their increased risk of survival and establishment under climate change. We found a total of 155 PPPs, the majority of which were platyhelminths, viruses and bacteria. While many of the identified PPPs were already known to occur in UK waters, PPPs currently absent from UK waters and with zoonotic potential were also identified. Results are discussed in the context of understanding potential impact, in addition to provision of evidence to inform risk assessment and mitigation approaches.

A new species of Trichodina lishuiensis n. sp. (Ciliophora: Trichodinidae) in urinary bladder of Odorrana schmackeri (Amphibia: Ranidae) from Zhejiang, China

Endoparasitic trichodinids are rather rare ciliates. In this study we describe a new species named Trichodina lishuiensis from the bladder of Odorrana schmackeri collected in Zhejiang, China, with the prevalence of 20% (9/45). We identified T. lishuiensis as a new species by morphological comparison and molecular analysis. The ciliates were observed using the dry-silver and protargol staining methods, as well as SEM (scanning electron microscopy). Trichodina lishuiensis is a small species (cell diameter 31.8-43.9 μm), with incompact denticles connection, medium-wide blades and thick rays. We also sequenced a 1712 bp-long fragment of the small subunit ribosomal RNA gene (SSU rRNA). Phylogenetic analyses showed that the new species clustered with Trichodina unionis. The route of transmission of Trichodina species in the urinary bladder remains a mystery. We hypothesize that the transmisison takes place during the amplexus, with eggs and sperm discharged from the cloaca, and that trichodinids 'accompany' the amphibian through its whole life cycle, but further studies are needed to test this hypothesis.

Integrative Studies on a New Ciliate Campanella sinica n. sp. (Protista, Ciliophora, Peritrichia) Based on the Morphological and Molecular Data, With Notes on the Phylogeny and Systematics of the Family Epistylididae

During an investigation on freshwater peritrichs, a new colonial sessilid ciliate, Campanella sinica n. sp., was isolated from aquatic plants in an artificial freshwater pond in Qingdao, China. Specimen observations of this species were performed both in vivo and using silver staining. C. sinica n. sp. is characterized by the appearance of the mature colony, which is up to 2 cm high and contains more than 1,000 zooids, the asymmetric horn-shaped zooids, strongly everted and multi-layered peristomial lip, the slightly convex peristomial disc, and the well-developed haplokinety and polykinety, which make more than four circuits of the peristome before descending into the infundibulum. The small subunit ribosomal DNA (SSU rDNA), 5.8s rDNA and its flank internal transcribed spacers (ITS1-5.8s rDNA-ITS2), and large subunit ribosomal DNA (LSU rDNA) are sequenced and used for phylogenetic analyses which reveal that the family Epistylididae Kahl, 1933 is non-monophyletic whereas the genus Campanella is monophyletic and nests within the basal clade of the sessilids. The integrative results support the assertion that the genus Campanella represents a separate lineage from other epistylidids, suggesting a further revision of the family Epistylididae is needed. We revise Campanella including the transfer into this genus of a taxon formerly assigned to Epistylis, which we raise to species rank, i.e., Campanella ovata (Nenninger, 1948) n. grad. & n. comb. (original combination Epistylis purneri f. ovata Nenninger, 1948). In addition, we provide a key to the identification of the species of Campanella.

Molecular characterization and phylogenetic analyses of Tripartiella macrosoma Basson and Van As, 1987 and Tripartiella obtusa Ergens and Lom, 1970 based on 18S rRNA gene sequence data

In the present study, we provided the first 18S rRNA gene sequence data of two Tripartiella species, Tripartiella macrosoma Basson and Van As, 1987 and Tripartiella obtusa Ergens and Lom, 1970, which were isolated from Tachysurus fulvidraco (Richardson, 1846) and Hemibarbus maculatus Bleeker, 1871 in Chongqing, China, respectively. Morphologically, both species fall within the morphometry range of the original descriptions and are very similar to the original populations in the overall appearance of the adhesive disc. Tripartiella macrosoma can be easily distinguished from the other Tripartiella species by possessing the denticle with a long strip and conspicuously inclined backward blade and a robust and short ray. Tripartiella obtusa is mainly characterized by a broad blade and a relatively long ray. Phylogenetically, T. macrosoma clustered with Trichodinella myakkae (Mueller, 1937) Raabe, 1950 and further with Trichodinella sp., which was sister to a group that includes four populations of Trichodinella epizootica (Raabe, 1950) Šrámek-Hušek, 1953; finally, they formed a small clade with T. obtusa. This result suggested that T. macrosoma had a closer relationship with Trichodinella spp. than with T. obtusa and T. obtusa diverged earlier than T. macrosoma and Trichodinella spp. By combining morphological and molecular data, the polyphyletic characteristics of Tripartiella and Trichodinella were further analyzed, and the results revealed that the validity of the genus Tripartiella is doubtful.

Fins infestation induced by Myxobolus xiantaoensis in yellow catfish Tachysurus fulvidraco Richardson, 1846: Some pathophysiological and molecular insights

The myxozoan parasite Myxobolus xiantaoensis is a fin pathogen of commercially important yellow catfish Tachysurus fulvidraco Richardson, 1846, in the freshwater ponds of China. In the present work, four geographical isolates of M. xiantaoensis were sampled from the fins of yellow catfish. It was found that the spores of four isolates exhibited few markable differences in morphometrics. The small subunit ribosomal DNA (SSU rDNA) sequences of four isolates were conspecific to the SSU rDNA sequence of M. xiantaoensis. No genetic level variation was observed, even in the characteristically more variable internal transcribed spacer (ITS) region. This absence of variability suggests high gene flow as a result of panmixia in the parasitic populations. ITS phylogeny placed four isolates of M. xiantaoensis in a clade together with myxozoans species infecting Siluriformes. The M. xiantaoensis infection inflicted severe hemorrhages on epidermis of ray-fins, which grew into inflammatory epithelial hyperplasia and lytic cartilage signs. The histochemical analysis of infected fins biopsies is characterized by damage of collagen components of cartilage, resulting in weakness, breaks, and missing fin rays. These tissue sections also had a remarkable inflammatory response around the fin cartilage, with the absence of mature spores and chondrocytes. These results indicate that the fin cartilage damage appeared before the development of tissue inflammation and the parasitic infestation of the fins. The present four geographical isolates of M. xiantaoensis were identified by a holistic approach of species characterization based on biological, morphological, and molecular evidence. These four isolates showed some morphological and genetic variations but within the intraspecific range.

Morphological and molecular identification of epibiontic sessilid Epistylis semiciculus n. sp. (ciliophora, Peritrichia) from Procambarus clarkia (Crustacea, Decapoda) in China

Data on sessilinasis from Procambarus clarkia are limited. This study investigates sessilid diversity in Hubei Province, China in 2016. Procambarus clarkia pereopods were covered by two sessilid morphotypes in April and May, and the gills were adhered by one of these two morphotypes (morphotype I) in January. Identifying the two morphotypes according to their morphological characters through live observations and protargol-stained method is difficult. Both morphotypes show almost identical morphological characteristics: zooids present vase-shaped, the length-to-width ratio is 2:1, the semicircle-shaped peristomial disk is evidently above the peristomial lip, single contractile vacuole is located below the peristomial lip, and the oral infraciliature shows identical arrangement which can be distinguished from other Epistylis. However, the morphometric data of the two morphotypes are significant different: body size of morphotype I is 78.9–103.8 × 32.1–54.6 μm, whereas that of morphotypes II is 136.7–171.5 × 60.9–88.0 μm. To further identify the two morphotypes, molecular regions including small subunit ribosomal DNA (SSU rDNA) sequences, large subunit ribosomal DNA (LSU rDNA) sequences, and ITS1-5.8S-ITS2 sequences were used. Results supported that the two morphotypes are single species of genus Epistylis rather than distinct species based in their distinct size ranges and temporal presence events. We assigned it the name E. semiciculus n. sp. with respect to the semicircular peristomial disk. Overall, these findings emphasized the importance of using molecular data to solve the identification confusion caused by ontogenetic processes. This study is the first morphological and molecular characterization of a sessilid isolated from P. clarkia under aquaculture conditions.

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The first identification of epibiontic sessilid from Procambarus clarkia.

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Different attachment sites of sessilids in spring and winter.

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Two morphotypes of a new Epistylis with significant different morphometric data.

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Species descriptions include morphological (vivo and stained) and molecular data.

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Present Epistylis distinguished by body shape, contractile vacuole and infraciliature.

First record of two ectoparasitic ciliates of the genus Trichodina (Ciliophora: Trichodinidae) parasitizing gills of an invasive freshwater fish, Micropercops swinhonis, in Tibet

Although high diversity of parasitic ciliates has been reported in China, little is known about the species from high altitude areas, especially in Tibet. To investigate the species of parasitic ciliates in Tibet, a project was initiated in the Chabalang wetland in 2013. Two Trichodina species, namely, Trichodina sp. and T. reticulata Hirschmann & Partsch, 1955, were isolated from gills of an invasive fish, Micropercops swinhonis for the first time. In the present study, we provided the morphological, morphometrical, and molecular characterizations of the two species and conducted the phylogenetic analyses of mobilids based on the small subunit ribosomal RNA gene (SSU rDNA) sequences. Both morphological characters and morphometric data of the T. reticulata agreed well with previous studies. Although two partial SSU rDNA sequences were obtained in the present study, only the sequence of T. reticulata population in the present study was thought to be reliable. The other sequence may not belong to the other species. Thus, we regarded the other species isolated in the present study as Trichodina sp. to avoid the wrong or confused species identification. Morphologically, Trichodina sp. is distinguished mainly by its large body shape with a broad adhesive disk, robust and obliquely quadrilateral blades, and well-developed rays. T. reticulata is mainly characterized with the 8-12 spherical or elliptical granules in the central zone of adhesive disk. Phylogenetic analyses consistently showed the two ectoparasites clustered with freshwater species of the genus Trichodina within the order Mobilida. Our study extended the host range of T. reticulata and supplemented the molecular data. Also, results reveal that invasion of exotic fish may cause a potential threat to native fish by introducing or dispersing parasitic ciliates.