Stereology reading protocol when using quantitative histology for the determination of sexual maturity in fish ovaries

This protocol was established for the evaluation of sexual maturity for exploited stock species, using quantitative histology (stereology). This document describes the reading method used on histological slides under the cross-platform QuPath. This document follows the work of different workshops that aimed to improve the compilation of data on sexual maturity. The WKMATCH (WorKshop for MATurity staging CHairs, 2012) and the WKASMSF (Workshop for Advancing Sexual Maturity Staging in Fish, 2018) defined a universal evaluation grid for sexual maturity staging of different species, including teleosteans. During the WKMATCH workshop, two main recommendations were made, underlining the need to improve and complete knowledge on sexual maturity, as well as to harmonize the practices used to determine these sexual phases. Another workshop, the WKMATHIS (WorKshop on sexual MATurity staging from HIStological tools) that took place in Caen in 2017, added new objectives : review the current knowledge on gonad histology, determine a sexual maturity scale at a cellular level, and histological studies should be made in order to improve the determination of sexual maturity on a macroscopic scale. This protocol, drawn from these workshops and their conclusions, offers guidelines on how to read histological slides through the use of stereology. As of June 2022, this protocol is linked to the MATO (MATurité Objectif des poissons par l’histologie quantitative) project, a study restricted to female gonad and the different cellular structures found inside the ovaries for different species (Pleuronectes platessa, Lepidorhombus whiffiagonis, Lepidorhombus boscii, Mullus surmuletus and Micromesistius poutassou). This protocol will present reading methods that favor an objective reading of histological slides, through stereology, and will allow less experienced readers to partake in this exercise. For a detailed description of the germinal cells, refer to the lexicon of the studied speci