Variability in the assignment of maturity stages of plaice (Pleuronectes platessa L.) and whiting (Merlangius merlangus L.) using macroscopic maturity criteria

This study investigates if a macroscopic maturity scale can be applied consistently, by examining the variability between and within 10 people who repeatedly assessed the sex and maturity stages of 80 plaice (Pleuronectes platessa L.) and 79 whiting (Merlangius merlangus L.) gonads. In most cases, agreement within assessors was not significantly higher than agreement between assessors, suggesting that variability was random and not due to differences in interpretation. This finding was supported by the fact that a significant bias was only found for one assessor. Some maturity stages were assigned quite consistently, while other stages were not defined objectively enough to be assigned reliably, even when fish were assessed repeatedly by the same person. For both species, well-defined maturity scales with fewer stages would be preferable over scales that distinguish a larger number of maturity stages. As maturity staging will always contain a form of subjective judgement, it should be subject to continuous quality control measures.