A telephone survey of eel fishermen regarding external lesions and mortalities of American eels (Anguilla rostrata) from Lake Ontario and the St. Lawrence River basin, Canada.
Signs of decreasing landings and recruitment have been observed during the last decade in American eels (Anguilla rostrata) from the St. Lawrence River basin, Canada. A study was undertaken to examine whether important manifestational diseases among commercial catches could be associated with these declines. During this survey, 56 fishermen from Lakes Ontario, Saint-François and Saint-Pierre, the Richelieu River, the Québec City area and the St. Lawrence Estuary were interviewed. Most fishermen from every area reported decreasing catches since the 1980s. Eel mortalities were reported from 1990 to 1992 in Lake Saint-François, Lake Saint-Pierre and the Québec City area, but in apparently lower magnitude than in the past decades. The lesions observed on dead eels in Lake Saint-François indicated that the cause of the mortalities might be associated with the upstream hydroelectric dam. Eels with 'scratches all over the body' were only observed in the St. Lawrence Estuary. Fishermen from almost every area reported that they had observed eels with 'crooked tail', 'humpback' and 'cut tail' in low frequency in 1992. The questionnaire data were validated by comparing some of the results of the questionnaire survey and a processing plant survey in 1992. The use of questionnaires for assessing fish diseases in commercial species is discussed. The results of this survey do not indicate that the health of the American eels from the St. Lawrence River basin is severely impaired. However, the magnitude of diseases and mortalities was probably underestimated.
A processing plant survey of external lesions of American eels (Anguilla rostrata) from Lake Ontario and the St. Lawrence River, Canada.
Signs of decreasing landing and recruitment were observed in the last decade in American eels (Anguilla rostrata) from the St. Lawrence River basin, Canada. In order to verify if the declines were associated with high prevalence of diseases among commercial catches, a total of 12243 eels captured in five commercial fishing sites were inspected at two processing plants in 1992. They were all examined for external lesions and palpated to detect vertebral deformities. Eels from Lakes Ontario, Saint-François and Saint-Pierre were mainly resident eels, while those from the Richelieu River and the St. Lawrence Estuary at Kamouraska were mainly mature migrating eels. Prevalences of every lesion observed were low (< or = 1%) at every site. Scratches all over the body were found only on eels from Kamouraska. Cutaneous ulcers were observed more frequently in the Richelieu River. Higher prevalences of vertebral deformities were found in mature migrating eels captured in Kamouraska and in the Richelieu River. Vertebral deformities were also observed more frequently among eels captured at the end of the 1992 fishing season in Kamouraska. Higher length, weight and/or age of mature migrating eels may be associated with higher prevalences of vertebral deformities among this group. These results do not indicate that the health of the American eels commercially captured in the St. Lawrence basin is severely impaired. However, the magnitude of diseases among the biological population is probably underestimated by such a survey.
Liver Pathology in fishes from the lower Elbe as a consequence of pollution
In flounder Platichthys flesus, ruffe Gyrnnocephalus cernua, and smelt Osmerus eperlanus, caught mainly during 1980 through 1983 in the Lower Elbe, a large number of serious pathological liver conditions were diagnosed. The predominant symptom was a shrinkage of liver cells, which spreads with advancing age and is increasingly accompanied by other degenerative changes, such as dissolution of the well-organized liver structure, blood clots, and tissue necroses. Neoplastic liver nodules were found in 32 % of sexually mature ruffe. Elbe flounders, which mature sexually shortly after migrating to their spawning grounds in the southern North Sea, still showed no signs of such nodules. In contrast, recent investigations of sexually mature flounders off the Dutch coast revealed occurrence rates as high as 10 %. Fishes from the River Eider, in which pollution is minimal, were effectively free from such liver damage. The livers of some 1 yr old flounders from the Lower Elbe, kept for 40d in uncontaminated water and fed on a diet free of harmful substances, showed signs of regeneration along with a decrease in chlorinated hydrocarbon content. Livers of other fishes kept under the same conditions maintained their high chlorinated hydrocarbon concentrations and continued to display the pathological liver symptoms. That the liver damage observed in Elbe fishes is due to high pollution levels receives support from 2 facts: (1) Other authors found similar pathological liver conditions in coastal regions where the pollution level was high; (2) liver conditions of this kind could be induced experimentally in fishes by PCBs in concentrations of the same order of magnitude as those recorded in the Lower Elbe.