An annotated list of the species of Gangesia Woodland, 1924 (Cestoda: Proteocephalidea), parasites of catfishes in Asia, with new synonyms and a key to their identification

Taxonomic summary of Schyzocotyle (Cestoda: Bothriocephalidae) with a redescription of Schyzocotyle nayarensis (Malhotra, 1983) from India

In this study, we use an integrative taxonomic approach to redescribe Schyzocotyle nayarensis (Malhotra, 1983) (Cestoda: Bothriocephalidae), based on newly collected specimens from the type-host Raiamas bola (Hamilton, 1822) (Cypriniformes: Danionidae) in Fulbari, Siliguri, West Bengal, India. The detailed morphological assessment, from whole mounts, histology and scanning electron microscopy, offers additional insights into the scolex structure, vitelline follicles, and egg morphology. Molecular data from this and previous studies corroborate the identity and systematics of S. nayarensis as a bothriocephalid closely related to the Asian Fish Tapeworm, Schyzocotyle acheilognathi (Yamaguti, 1934). This study elucidates the historical context and taxonomic ambiguities surrounding S. nayarensis, emphasizing the key role of the scolex in both generic and species identification. Amendments to the diagnosis of Schyzocotyle Akhmerov, 1960 are proposed. A differential diagnosis of the two valid species within the genus, namely S. acheilognathi and S. nayarensis, is also provided. An evaluation of the taxonomic status of Bothriocephalus teleostei Malhotra, 1984, and Capooria barilii Malhotra, 1985 suggests that they may be S. nayarensis. Finally, we posit that none of the ten species of Ptychobothrium Lönnberg, 1889 described from Indian freshwater teleosts belong to this genus but instead appear to be a mix of species belonging to Schyzocotyle, Senga Dollfus, 1934, and possibly even Proteocephalidae La Rue, 1911; all require further study based on newly collected, properly fixed specimens and an integrated taxonomic approach. Finally, future survey studies may reveal hidden diversity of Schyzocotyle species in Indian cyprinoids.

Unlocking the Biological Enigma: Influence of Host Length and Infection Site on Parasite Abundance in Ompok bimaculatus

PURPOSE

The influence of two key factors, host length and infection site, on the host-parasite interaction in Ompok bimaculatus (Butter catfish) from Mukutmanipur Dam Lake, were investigated.

METHODS

Present study involved 192 specimens of Ompok bimaculatus with varying body lengths, subjected to diverse statistical analyses. One-way analysis of variance (ANOVA) was performed for the parasite numbers for three groups (cestode, nematode and trematode). Subsequently, we conducted one-way permutational multivariate analysis of variance (PERMANOVA) followed by pairwise test to assess parasite numbers across three body sites (intestine, mesentery, and bodycavity), employing the Bray-Curtis index. Additionally, Principal Coordinate Analysis (PCoA) for the same dataset was performed using the same index. Linear regression analysis was performed for the fish length-cestode number, fish length-nematode number, fish length-trematode number and fish length-total parasite number.

RESULTS

One-way ANOVA revealed no significant differences in parasite numbers among the three endo-helminth groups (cestode, nematode, and trematode). The results of PERMANOVA revealed significant differences in parasite numbers across the three body sites of the host fishes (groups) (F = 9.41, p = 0.0001). Pairwise tests further demonstrated significant differences between the intestine-mesentery, intestine-body-cavity, and mesentery-body-cavity. Additionally, Principal Coordinate Analysis (PCoA) unveiled a significant relationship between infection site and parasite number. However, linear regression analysis examining the relationship between fish length and parasite abundance indicated no significant associations.

CONCLUSIONS

Through a detailed exploration of the statistical analyses, we provide insights into the host-parasite interaction, elucidating both established knowledge and novel findings in fish parasitology.

Manual for the study of tapeworms (Cestoda) parasitic in ray-finned fish, amphibians and reptiles

Based on long-term and often frustrating experiences with the poor quality of tapeworms (Cestoda) collected throughout the world for taxonomic and phylogenetic studies, and considering the increasing obstacles to obtaining new material, a simple, easy-to-use and illustrated methodological guide (manual) is provided. It focusses mainly on key steps in examining hosts, collecting cestodes from poikilothermous vertebrates except elasmobranchs, i.e., from ray-finned fish (Actinopterygii), amphibians and 'reptiles' (a paraphyletic group comprising all sauropsids except birds), and fixing them for subsequent morphological and molecular study. It is proposed that the following methodological points should be followed: (i) ideally only freshly euthanised hosts (not previously frozen) should be used for parasitological examination; (ii) hosts examined should be documented by photographs; host tissue should also be preserved for future genotyping if necessary; (iii) tapeworms should be detached carefully to keep the scolex intact and properly cleaned before fixation; (iv) a small piece of cestode tissue should be always preserved in molecular grade ethanol for DNA sequencing; (v) tapeworms should be fixed as quickly as possible after collecting them and while they are still alive, always using hot (heated) fixatives; this prevents unnatural contraction or deformation and ensures uniform fixation; (vi) each sample (vial) should be properly labelled (a unique code should be given to every cestode sample); (vii) vouchers of sequenced specimens (hologenophores or paragenophores) should always be preserved for identification, and deposited in internationally recognised collections. It is hoped that this guide helps researchers and students to properly process valuable material of cestodes to make it suitable for reliable identification including genotyping and comparative anatomy, which is a prerequisite for any subsequent ecological, biogeographical, phylogenetic life cycle or molecular study.

Fish tapeworms (Cestoda) in the molecular era: achievements, gaps and prospects

The tapeworms of fishes (Chondrichthyes and Actinopterygii) account one-third (1670 from around 5000) of the total tapeworm (Platyhelminthes: Cestoda) species diversity. In total 1186 species from 9 orders occur as adults in elasmobranchs (sharks, rays and chimaeras), and 484 species from 8 orders mature in ray-finned fishes (referred to here as teleosts). Teleost tapeworms are dominated by freshwater species (78%), but only 3% of elasmobranch tapeworms are known from freshwater rays of South America and Asia (Borneo). In the last 2 decades, vast progress has been made in understanding species diversity, host associations and interrelationships among fish tapeworms. In total, 172 new species have been described since 2017 (149 from elasmobranchs and 23 from teleosts; invalidly described taxa are not included, especially those from the Oriental region). Molecular data, however, largely limited to a few molecular markers (mainly 28S rDNA, but also 18S and cox1), are available for about 40% of fish tapeworm species. They allowed us to significantly improve our understanding of their interrelationships, including proposals of a new, more natural classification at the higher-taxonomy level (orders and families) as well as at the lower-taxonomy level (genera). In this review, we summarize the main advances and provide perspectives for future research.

Characterization and phylogenomics of the complete mitochondrial genome of the polyzoic cestode Gangesia oligonchis (Platyhelminthes: Onchoproteocephalidea)

The order Onchoproteocephalidea (Eucestoda) was recently erected to accommodate the hook-bearing tetraphyllideans and the proteocephalideans, which are characterized by internal proglottization and a tetra-acetabulate scolex. The recognized subfamilies in the Proteocephalidae appeared to be non-monophyletic based on 28S recombinant DNA (rDNA) sequence data. Other molecular markers with higher phylogenetic resolution, such as large mitochondrial DNA fragments and multiple genes, are obviously needed. Thus the mitochondrial genome of Gangesia oligonchis, belonging to the putative earliest diverging group of the Proteocephalidae, was sequenced. The circular mitogenome of G. oligonchis was 13,958 bp in size, and contained the standard 36 genes: 22 transfer RNA genes, two rRNA genes and 12 protein-coding genes, as well as two major non-coding regions. A short NCR and a large NCR (lNCR) region were 216 bp and 419 bp in size, respectively. Highly repetitive regions in the lNCR region were detected with that of 11 repeat units. The mitogenome of G. oligonchis shared 71.1% nucleotide identity with Testudotaenia sp. WL-2016. Phylogenetic analyses of the complete mitochondrial genomes with Bayesian inference and maximum likelihood methods indicated that G. oligonchis formed a sister clade with Testudotaenia sp. WL-2016 with maximum support. The ordinal topology is (Caryophyllidea, (Diphyllobothriidea, (Bothriocephalidea, (Onchoproteocephalidea, Cyclophyllidea)))). The mitogenomic gene arrangement of G. oligonchis was identical to that of Testudotaenia sp. WL-2016. Both mitogenomic and nuclear sequence data for many more taxa are required to effectively explore the inter-relationships among the Onchoproteocephalidea.