Abstract

Parasites are indicators of the physiological conditions of fish as population components. Under normal conditions, an equilibrium can be observed in the host - parasite relationship, which secures mutual development of both individuals. Due to this and the specificity shown by some parasites for their host, it has been reported that larval forms of parasites can be used as biological tags, as well as indicators of specific characteristics of hosts in relation to their migratory route. The commercial fishery of billfish in Venezuela is very recent, and thus the knowledge of important aspects of their biology and ecology lacks. This report offers information about the parasites found in two species of billfish (white marlin, Tetrapturus albidus, and the sail fish, Istiophorus albicans) and in the swordfish (Xiphias gladius), captured by artisanal and industrial long line fishermen in Venezuela. A total of 60 intestinal tracts, gills and gonads were parasitologically analyzed. In the white marlin, 1129 parasites were observed, with 100% prevalence, of which 1121 were Nematoda, 2 Cestoda and 6 Acantocephala. Among the Nematoda, 98% were immature forms and the other 2% were individuals of the genera Raphidascaris, Paranisakis and Neogoezia. The mean intensity of infection was 50 Nematoda/fish. The samples of swordfish had a total of 1486 Nematoda with a 69% prevalence of immature forms and 1% of mature Nematoda of the genus Raphidascaris. The mean intensity of infection was 66 Nematoda/fish. In the sail fish, 675 Nematoda were found with 48% prevalence and a mean intensity of infection of 80 Nematoda/fish. There were blood red intestinal adherence, possibly due to bacterial infections. No parasites were found in gills and gonads of the three species. The presence of immature Nematoda, frequent in fish of the families Scombridae, Clupeidae, Caranguidae, as well as in octopus and squids, supports the predatory characteristic of the billfish and swordfish analysed, and would suggest that the parasites were transported by the prey fish species.

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