This report describes a viral epidemiological study of wild fish around the Gulf of Cadiz (southwestern Iberian Peninsula) and is focused on infectious pancreatic necrosis virus (IPNV), viral hemorrhagic septicemia virus (VHSV), and viral nervous necrosis virus (VNNV). One fish species (Chelon labrosus) was sampled inside the gulf, at the mouth of the San Pedro River. Another 29 were sampled, in three oceanographic campaigns, at sites around the Bay of Cadiz. The fish were processed individually and subjected to isolation in cell culture and molecular diagnosis. VHSV was not isolated from any species. Thirteen IPNV-type isolates were obtained from barracuda (Sphyraena sphyraena), axillary seabream (Pagellus acarne), common two-banded seabream (Diplodus vulgaris), common pandora (P. erythrinus), Senegal seabream (D. bellottii), and surmullet (Mullus surmuletus). Six VNNV isolates were obtained from axillary seabream, common pandora, black seabream (Spondyliosoma cantharus), red mullet (Mullet barbatus), Lusitanian toadfish (Halobatrachus didactylus), and tub gurnard (Chelidonichtys lucerna). In the river mouth, viruses were detected only after reamplification, obtaining prevalence percentages of IPNV and VNNV (44.4 and 63.0%, respectively) much higher than those observed in the oceanographic campaigns (25.7 and 19.6%, respectively). The opposite results were obtained in the case of VHSV after reamplification: 11.1% in the river mouth and 43.6% in the oceanic locations. Analyzing the results with respect to the proximity of the sampling sites to the coast, an anthropogenic influence on wild fish is suggested and discussed. The type of viruses and the presence of natural reassortants are also discussed.
Microbial pathogens and potential hosts have coexisted in the marine environment for a long time. This coexistence allows the achievement of a balance between the pathogen and its host: The pathogen self-limits its virulence to reduce the negative effect on specific hosts, and the host uses defense strategies to minimize the negative consequence of the infection. The stressful conditions of intensive culture, however, usually break that equilibrium, and consequently, disease episodes probably occur more frequently than in natural environments.Among pathogens, the relevance of viral fish diseases relies on the high morbidity and mortality rates of infections and on the lack of effective treatments and prophylactic measures. In addition, several factors such as the vertical transmission of some fish viruses and the ability to establish chronic infections or carrier states among survivors must also be considered (1).The Ninth Report of the International Committee on Taxonomy of Viruses (2) formally recognizes 40 species of fish viruses in 11 taxonomic families. However, only a few studies of wild fish viruses have been performed, in contrast to those done with cultured or ornamental fish. This is probably due to the important losses that viral diseases cause in cultured fish. Moreover, since diseased or moribund animal...