The purpose of this study is to examine the use of a Weight of Evidence (WOE) approach to evaluate fish health status and biological impacts (BEs) of pollutants for assessing ecosystem health, and to consider its possible application in support of the Marine Strategy Framework Directive (MSFD). External fish disease, liver histopathology, and several biomarkers of contaminant exposure were measured in two flatfish species from four locations in Ireland, including 7-Ethoxy Resorufin O-De-Ethylase (EROD), acetylcholinesterase (AChE), bile metabolites, Vitellogenin (VTG), and Alkali Labile Phosphates (ALP). PCB levels in fish liver were below OSPAR environmental assessment guidelines, indicating that contaminant levels in fish were typically low (EAC). There were consistent findings in fish with low PCB levels, EROD, and PAH bile metabolite levels. The relative frequency of liver lesions connected with the carcinogenic pathway was greatest in Dab from Cork, Dublin, and Shannon. Water contamination causes pathological alterations in fish. Histology, as a biomarker of pollutant exposure, is a valuable technique for assessing the level of contamination, particularly for sub-lethal and chronic impacts. However, a consistent technique for the description and assessment of histological alterations, primarily for application in freshwater fish, is currently absent. The authors of this work suggest a standardised technique for assessing histological results that may be used to many organs. The technique is based on two factors: The extent of a pathological change is scored with a'score value,' and The pathological relevance of this alteration is characterised as a 'importance factor.' The total of the multiplied score values and significance factors of all diagnosed alterations yields various indices.
