Workshop on the maturity staging of lemon sole (Microstomus kitt) (WKMSLEM)

The main task of the workshop on maturity staging of lemon sole (WKMSLEM) was to work on quality assurance of maturity staging of lemon sole (Microstomus kitt) by trial (staging exercises), discussion, retrial, and providing descriptions for the different maturity stages. In total, four staging sessions took place. The first was online before the workshop, using images (SmartDots). During the workshop, all participants staged fresh fish (2x) and from pictures (1x). High-resolution digital slides from histology were available for most fish used in the picture staging, as a reference stage. The overall percentage agreement between stagers improved during the workshop from 67.6% to 71.8% for the picture stagings. For both stagings, agreement between stagers and histology remained low: 50.6% to 51.8%. The stagers agreed in fresh fish stagings for 66.1% and 66.8% respectively. The interpretation of the stages was slightly complicated because the fish from the auction came from a different area (7.f and 7.g, Celtic Sea) than the stagers’ prime area of attention (4.b and 4.c, North Sea). The outcome of the discussions after the staging exercises formed the basis for the maturity descriptions. Throughout the staging exercises the descriptions were refined. Reference pictures of the stages will be added to a SmartDots reference set, accessible to all. Lemon sole is a batch spawner, so one fish spawns multiple times within the season. Spawning season runs from May until October. The development cycle differs for males and females. The long spawning season, the batch spawning, and the discrepancy in development of male and female lemon sole, lead to confusion in identification of maturing lemon sole. For stock assessment purposes it is relevant to know if a fish takes part in the spawning (distinction between stage immature and maturing/spawning/regressing). It could be questioned if defining a specific stage adds information, or only creates a perceived detail level. Due to the long spawning season, it is advised to stage maturity of lemon sole throughout the year, taking into account that reliable staging of maturing lemon sole may be difficult. The group provided feedback on the workshop material, pictures as well as fresh fish, and provided suggestions for additional information to manuals.