Sources of measurement error in assays of EROD activity of fish for biological effects monitoring

The paper describes the technical, procedural and biological aspects of 7-e thoxyresorufin O-deethylase (EROD) activity measurements in dab. Limanda li manda, from the North Sea. Several sources of measurement error in assays o f EROD activity measurements for biological effects monitoring exercises co uld be defined, particularly for assay conditions, sample storage and sampl ing. In addition to variability caused by technical errors, biological feat ures inherent in the surveyed fish may lead to even more severe errors in E ROD activity measurements. This is particularly true of the choice of sampl ing time. Disregarding the species-specific spawning periods may lead to a loss of activity by a factor of as much as 90 in females and 40 in males, t hus making it necessary to design sampling surveys appropriately.