New records and insights of digenean trematodes parasitising piscivorous birds (Pelecaniformes and Suliformes) in Lake Victoria Basin, Tanzania

Abstract

Trematodes are parasitic flatworms that utilise multiple hosts during their life cycles. Their presence reflects the diversity of available host species, making them valuable indicators of ecosystem health. However, our understanding of their occurrence, diversity and distribution among fish-eating birds in the Lake Victoria Basin (LVB) remains limited. This study aimed to investigate intestinal trematodes infecting the fish-eating bird species Ardea cinerea, Ardea alba, Phalacrocorax carbo and Scopus umbretta in the LVB, using morphological and molecular markers, comprising cytochrome c oxidase subunit I (cox1 mtDNA), internal transcribed spacer region (ITS1–5.8S–ITS2) and 28S rDNA. Both morphological and molecular analyses identified nine operational taxonomic units, of which five were identified to species level: Holostephanus dubinini (Cyathocotylidae) infecting Ph. carbo; Patagifer vioscai (Echinostomatidae) from Ar. cinerea; Apharyngostrigea pipientis (Diplostomidae) and Tylodelphys mashonensis (Diplostomidae), infecting Ar. cinerea and Ar. alba; Haplorchis pumilio (Heterophyidae), residing in S. umbretta and Ph. carbo; and Cardiocephaloides sp. (Diplostomidae), infecting Ph. carbo, identified to genus level. Diplostomidae gen. sp. OK-2019, Diplostomidae gen. sp. FDC-2025 and Posthodiplostomum sp. FDC-2025 are not only new geographical records but also do not match existing genetic data. Hence, the current study has revealed the presence of diverse trematode taxa in piscivorous birds from the LVB and highlights the inadequacy of trematode genetic reference libraries, underscoring the need to expand molecular repositories for African trematodes.