Liver histopathology in Baltic eelpout (Zoarces viviparus) – A baseline study for use in marine environmental monitoring

The use of liver histopathology in various fish species as a biomarker in marine monitoring programmes to assess the biological effect of exposure to anthropogenic contaminants is well established. However, although the eelpout (Zoarces viviparus) has repeatedly been recommended as an appropriate bioindicator for monitoring purposes in the Baltic Sea, information on histopathological liver alterations of this species is scarce. In order to obtain an overview, a total of 1070 eelpout, collected in the period between spring 2001 and winter 2010 from 34 sampling sites distributed over large parts of the Baltic Sea, were histologically analyzed. Liver lesions were recorded and classified according to established liver lesion categories. A high prevalence of non-specific and early toxicopathic non-neoplastic hepatic lesions was recorded. In contrast, pre-neoplastic lesions were observed only in rare cases and neoplastic changes were absent. A comparison with published data on other fish species revealed that the observed alterations may indicate effects of environmental stressors including contaminants. The results of the present study, thus, support the application of eelpout liver histopathology in environmental monitoring.

► This manuscript provides the first comprehensive liver histopathology of eelpout.
► Liver pathology is dominated by non-specific and inflammatory lesions.
► Livers displayed high prevalences of toxicopathic non-neoplastic liver lesions.
► Low prevalences of pre-neoplastic lesions and no neoplasms were observed.
► Eelpout liver histopathology is a suitable technique for environmental monitoring.