Transversotrema patialense var. hafniensis infection in Poecilia reticulata by cercariae released from Melanoides tuberculata in Denmark: Implications for fish health and bioinvasion

Abstract

Abstract Background Exotic and ornamental fish are highly popular companion animals in industrialized human societies resulting in a significant transcontinental trade of fish, invertebrates or aquatic plants. A major issue is the diseases associated with these organisms as they have a major impact on health of the fish in both public and private household aquaria. A secondary issue is the trade with these products, which potentially may expand the distribution area and spread a range of diseases to new habitats. Results We here describe how Poecilia reticulata Peters, 1859 (guppy), produced in a private household aquarium, were invaded by cercariae of an exotic trematode released by imported snails. The fish presented with severe clinical signs (tremor, flashing, scraping of body against objects). A standard parasitological examination and morphometric identification showed the disease to be caused by scale pocket infections with a species within the genus Transversotrema patialense (Soparkar, 1924), an exotic digenean trematode. Molecular identification by PCR, sequencing and BLAST analysis indicated that the parasite was an undescribed variant and the isolate was therefore named T. patialense var. hafniensis. Conclusions GenBank sequences for species within the genus Transversotrema are sparse and fragmented and we here present the entire 2646 bp sequence of encoding ribosomal RNA (partial 18S, ITS1, 5.8 S, ITS2, partial 28S) and a 1107 bp sequence of mitochondrial DNA (CO1). These are recommended for future diagnostics use and separation of sister species within T. patialense sensu lato. The fish were not purchased from a pet shop but produced in the home aquarium. This indicated that an infection pressure existed in the aquarium, where the source of infection was found to be exotic intermediate host snails Melanoides tuberculata (Müller, 1774), which originally were imported and purchased from a pet shop. They were recovered from the facility and shown to release infective cercariae, which infected naïve guppies. We frame that trade with infected snails may not only challenge the health of fish in aquaria but also represent a risk for spread of exotic fish diseases to new geographic regions where climate changes may facilitate their establishment.