This protocol was established during project MATO (MATurité Objective des poissons par l’histologie quantitative) for the evaluation of sexual maturity of exploited stock species, as well as to harmonize the sampling process of gonad extraction before the mounting between slide and slip of the gonad sections. 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) defined a universal evaluation grid for sexual maturity staging of different species. During this workshop, two main recommendations were made, underlining the need to improve and complete the knowledge on sexual maturity, as well as to harmonize the practices used to determine these sexual phases. This sampling protocol will be restricted to the female gonad of the megrim.