The age of all herring used for the Marine Monitoring Programme for Contaminants in Marine Biota are determined in order to be able to normalize fish to a certain age (although age-normalization is currently not included in the contaminant time trend analysis). Historically, scales are used for age reading, which has the advantage that the fish does not need to be opened or thawed in order to do an age determination and specimen selection for the programme. However, other labs have for the last decades started using otoliths for age determination instead. This method is thought to be more accurate. Otoliths can either be read direct under a microscope or they can be sliced and stained before reading. Using otoliths has furthermore been suggested to be faster than for scales.The aim for the project was therefore to 1) test if we could find an effective and fast method for removing otoliths from herring, 2) evaluate if reading otoliths would save time compared to reading scales and 3) to compare the result from the two methods (age from otolith and scale) to see if there was a bias in the “scale age”. Our focus was for this report on reading the otoliths directly under a microscope.An earlier study conducted at the museum also evaluated the use of scales versus otoliths for age determination. In this study the otoliths were sliced and stained, which means that the two studies are not one to one comparable. The focus on the previous study was also limited to our 3rd aim and did not evaluate the time or otolith removal components.