Further evidence of the southern Mediterranean medicinal leech Hirudo verbana (Annelida, Hirudinea) feeding on fish, with a review of the use of fish hosts by Hirudo spp.

Abstract

Although often considered primarily hematophagous on mammalian blood, the leeches belonging to the genus Hirudo can feed on several other vertebrate hosts. However, to date, little is known about the feeding ecology of medicinal leeches in the wild, and the few available observations mostly deals with the European medicinal leech, Hirudo medicinalis. Since even closely related Hirudo species have different functional morphology and ecological preferences, the observations carried out on one species cannot be automatically generalized to the other medicinal leeches, and targeted surveys must be realised to better understand the feeding habits of these leeches. A wide geographical belt ranging from the Iberian Peninsula to the Caucasus and Central Asia is inhabited by the southern European medicinal leech, Hirudo verbana. Although quantitative data are missing, the species seems characterized by a general decline throughout its distribution range, whose causes are not fully understood. Accordingly, a better understanding of H. verbana dietary composition is crucial to characterise its role in the trophic webs of the ecosystems it inhabits, with important consequences for the correct management of the populations of the species. Here, we report the observation of Hirudo verbana feeding on fish in the wild in southern Italy. This observation constitutes one of the first direct evidences of the species using fish as host organisms, since to date wild H. verbena had been observed mostly feeding on amphibians and mammals. Such information is useful to better characterise the diet of the wild populations of H. verbana, and to understand the trophic resources which could be exploited by the species in different ecosystems. Finally, a review of all the available evidence dealing with the use of fish as hosts organisms by Hirudo spp. is carried out.