Spiral Valve Parasites of Selected Tropical Pelagic Elasmobranchs from the Western North Atlantic Ocean.

Concerns regarding population status of many elasmobranchs have prompted recent investigations into less obvious sources of declines, such as the incidence of mortality due to parasites. Endoparasite (internal) loads in the elasmobranch spiral valve may be a source of such unaccounted mortality and morbidity by both inhibiting nutrient uptake and stimulating inflammatory responses within the gastrointestinal tract in the host. The species studied include the night shark ( Carcharhinus signatus ), silky shark ( Carcharias falciformis ) and pelagic stingray ( Pteroplatytrygon violacea ), none of which have been previously examined for full endoparasite fauna or total endoparasite loads. Specimens were obtained as incidental by-catch aboard pelagic longline fishing vessels operating in offshore tropical western North Atlantic Ocean waters from September 2008 and December 2009. Spiral valves were dissected from the elasmobranchs at sea and preserved whole in a 90:10 seawater:buffered formalin solution. Parasites were manually extracted in the laboratory from preserved spiral valves, then individually stained and mounted for identification. Total spiral valve parasite loads were compared against the total length and weight of the host; however, preliminary results show no relationship between these factors. Similarly, no correlations have been observed in comparisons of parasite load to species, sex, or seasonality. To date, 128 elasmobranchs were examined, yielding over 600 parasites. The majority have been cestodes, although trematodes and nematodes are also represented throughout the samples. These results have important implications through the establishment of baseline values for expected spiral valve parasite load and species compositions for pelagic shark and stingray hosts.