Location: Warmwater Aquaculture Research UnitTitle: Genetic sequence data identifies the cercaria of drepanocephalus spathans Digenea echinostomatidea a parasite of the double-crested cormorant Phalacrocorax auritus with notes on its pathology in juvenile channel catfish Ictal Author
Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/20/2012
Publication Date: 10/1/2012
Citation: Griffin, M.J., Khoo, L., Quiniou, S., O'Hear, M., Pote, L., Greenway, T., Wise, D. 2012. Genetic sequence data identifies the cercaria of drepanocephalus spathans Digenea echinostomatidea a parasite of the double-crested cormorant Phalacrocorax auritus with notes on its pathology in juvenile channel catfish Ictal. Journal of Parasitology. 98:967-972. Interpretive Summary: Pond-raised catfish with poor feeding activity were evaluated for possible underlying health issues. Initial health screenings ruled out Bolbophorus damnificus, a parasite commonly associated with reduced production, prompting further investigations. Challenge experiments and DNA analysis demonstrated Drepanocephalus spathans, a parasite previously thought inconsequential, also has adverse effects on catfish health. Both parasites use the marsh ram’s-horn snail as part of their life cycle.These findings reinforce the need for adequate snail control measures to reduce the incidence of these parasites on catfish farms.
Technical Abstract: In the summer of 2010, a catfish producer in the Mississippi Delta contacted the Fish Health Laboratory of the National Warmwater Aquaculture Center in Stoneville, MS regarding several ponds suspected of having trematode infections because of poor feeding activity. Fish and snail populations were evaluated for the presence of Bolbophorus damnificus, which can have deleterious effects on catfish production even in light infestations. Fifty channel catfish (Ictalurus punctatus) were sampled from each pond and examined grossly for the presence of B. damnificus metacercaria. Ram’s-horn snails (n=500) were collected from the pond margins, transported to the laboratory, placed in individual vials of sterile-filtered pond water and examined for the presence of Bolbophorus sp. cercaria. Metacercaria were not observed on any of the examined fish and the number of snails shedding Bolbophorus-type cercaria were negligible (<1%). These observations ruled out the likely involvement of B. damnificus as the cause of poor feeding activity. However a large number of snails (>20%) were shedding an unidentified xiphidio-type cercariae previously thought to be inconsequential to catfish health. A preliminary challenge cohabiting channel catfish with snails actively shedding the unidentified cercaria resulted in death of some fish. A second cohabitation trial yielded similar results, as did a third challenge of 250 cercariae/fish. Histopathology revealed developing metacercariae concentrated in the cranial region especially within the branchial chamber with several at the base of the branchial arches within or adjacent to blood vessels, possibly the proximate cause of death. Molecular analysis matched the cercaria to Drepanocephalus spathans (Digenea: Echinostomatidae), a parasite of the Double-crested Cormorant, a piscivorous bird endemic on most catfish farms. Identification of another trematode besides B. damnificus that can have negative impacts on catfish health further supports the need for adequate snail control programs to reduce trematode prevalence on commercial catfish operations.