North and South American Haplotypes ofDrepanocephalus auritus(Digenea: Echinostomatidae) Are Released fromBiomphalaria havanensis(Mollusca: Planorbidae) Inhabiting Catfish Aquaculture Ponds in Mississippi, U.S.A.

Abstract

Trematodes of the subclass Digenea are a major impediment to catfish aquaculture in the southeastern United States. Catfish production ponds are ideal feeding grounds for piscivorous birds, and given the variety of aquatic snails that inhabit these ponds, they offer a prime environment for the propagation of digenetic life cycles. In July 2014, snails morphologically consistent with Biomphalaria havanensis L. Pfeiffer, 1839, were collected from 2 different catfish production ponds in the catfish farming region of eastern Mississippi. These snails were refractory to Schistosoma mansoni Sambon, 1907, infection, and phylogenetic analyses based on internal transcribed spacer (ITS)1 and ITS2 fragments placed the snails within the B. havanensis/obstructa complex. Some (1.5%) of these snails shed cercariae morphologically and molecularly consistent with Drepanocephalus auritus Kudlai, Kostadinova, Pulis, and Tkach, 2015 (formerly reported as Drepanocephalus spathans Dietz, 1909), an echinostomatid parasite of the double-crested cormorant Phalacrocorax auritus Lesson, 1831, and channel catfish Ictalurus punctatus Rafinesque, 1818. Juvenile channel catfish were challenged individually with ∼275 cercariae of D. auritus per fish, resulting in limited mortality (2 out of 10 fish). Surviving fish were euthanatized 7 d postchallenge, and the presence of metacercariae was confirmed histologically. Parasite-associated pathology was consistent with previous studies. Subsequent molecular analysis of 5 different gene targets confirmed morphological identifications. Previous research has suggested the existence of discrete North American and South American haplotypes of D. auritus. Mitochondrial cytochrome c oxidase subunit 1 and nicotinamide adenine dinucleotide dehydrogenase subunit 1 sequences demonstrated that both haplotypes were released by snails in this study, suggesting a broader distribution of these genetic variants than previously thought. Along with Planorbella trivolvis Say, 1817, this work identifies a second snail species common to catfish aquaculture ponds that releases D. auritus infective to juvenile channel catfish and is the first report of B. havanensis as an intermediate host for D. auritus in North America.