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

Review

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

Tomáš Scholz et al. Parasitology. 2022 Dec.

Abstract

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.

Keywords: DNA sequencing; Distribution; elasmobranchs; host associations; pathogens; phylogenetic relationships; ray-finned fish; species diversity; taxonomy.

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Conflict of interest statement

The authors declare there are no conflicts of interest.

Figures

None
Graphical abstract
Fig. 1.
Fig. 1.

Species diversity of fish tapeworms (elasmobranch tapeworms in blue, teleost tapeworms in green): (A) cumulative curve of species of fish tapeworms described since 1776; (B) numbers of species of fish tapeworms described every year since 1970; note steady or even slowly lowering rate of description of new species of teleost tapeworms within the last 50 years.

Fig. 2.
Fig. 2.

Scanning electron micrographs of scoleces of representatives of orders of fish tapeworms: (A) Archigetes vadosus (Caryophyllidea) from Ictiobus bubalus, USA; (B) Diplocotyle olrikii (Spathebothriidea) from Myoxocephalus scorpius, off Svalbard Archipelago, Norway; (C) Haplobothrium globuliforme (Haplobothriidea) from Amia calva, USA; (D) plerocercoid of Dibothriocephalus latus (Diphyllobothriidea) from Perca fluviatilis, Italy; (E) Halysioncum reginae (Diphyllidea) from Pastinachus ater, off Madagascar; (F) Pterobothrium sp. (Trypanorhyncha) from Styracura schmardae, off Belize; (G) Kirstenella gordoni (Bothriocephalidea) from Heterobranchus bidorsalis, Kenya; (H) plerocercoid of Clistobothrium sp. 3 of Caira et al. (2020a, 2020b) (Phyllobothriidea) from Oncorhynchus gorbuscha, off Alaska; (I) Gangesia bengalensis (Onchoproteocephalidea I – Proteocephalidae) from Wallago attu, India; (J) Nippotaenia perccotti (Nippotaeniidea) from Perccottus glenii, Slovakia; (K) Ichthyolepis africana (Cyclophyllidea: Dilepididae) from Marcusenius macrolepidotus, South Africa; (L) merocercoid of Neogryporhynchus lasiopeius (Cyclophyllidea: Gryporhynchidae) from Tilapia sparrmanii, Zimbabwe.

Fig. 3.
Fig. 3.

Phylogenetic relationships of tapeworms (Cestoda); modified from Caira et al. (2014) and updated from Caira and Jensen (2017). A single species of adult cyclophyllideans was found in teleosts (host pictogram in parentheses). Freshwater hosts in green, marine hosts in blue (combined if tapeworms occur in both environments considering proportion of their species).

Fig. 4.
Fig. 4.

Pie chart documenting species diversity of fish tapeworms, i.e. proportion of species numbers of individual orders of fish tapeworms.

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  • Fish parasites (special issue).

    Sayyaf Dezfuli B, Scholz T. Sayyaf Dezfuli B, et al. Parasitology. 2022 Dec;149(14):1811-1814. doi: 10.1017/S0031182022001433. Epub 2022 Oct 13. Parasitology. 2022. PMID: 36226653 Free PMC article.

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