Gastrointestinal Parasites of Selected Tropical Pelagic Elasmobranchs and Mesopelagic Teleosts

Natural mortality is a poorly known aspect of fisheries biology, despite its importance in stock assessments and population analysis. Of the many potential sources of mortality and morbidity in fishes, the effects of gastrointestinal parasites is perhaps the least studied. Parasite loads in the elasmobranch spiral valve and teleost fish gastrointestinal tract may both inhibit nutrient uptake and stimulate an inflammatory response in the host. The gastrointestinal parasites of several tropical pelagic elasmobranchs including dusky, silky, and night sharks ( Carcharhinus obscurus, C. falciformis , and C. signatus ), the pelagic stingray ( Pteroplatytrygon violacea ) and the mesopelagic fishes snake mackerel ( Gempylus serpens ), oilfish ( Ruvettus pretiosus ), and escolar ( Lepidocybium flavobrunneum ) are described from the South Atlantic Bight in the western North Atlantic. Species found to date include nematodes, trematodes and cestodes, and their potential transmission vectors are being explored. Total gastrointestinal parasite loads are compared against the size (length and weight) of the host, showing no relationship for pelagic elasmobranchs and only a weak relationship for mesopelagic teleosts. To date, 60 elasmobranch specimens have been sampled with a yield of approximately five parasites and approximately 20 mesopelagic teleosts have been sampled, yielding approximately 80 total parasites, the majority being nematodes.