Comparing Macroscopic and Quantitative Histological Methods to Determine Sexual Maturity in the Female European Plaice, Pleuronectes platessa Linnaeus, 1758

Two methods (macroscopic and quantitative histology) to determine sexual maturity are described in this paper, with an emphasis on the methods used in stereology. Based on a point counting grid (Glagolev’s method), ovarian cellular structures were quantified throughout the whole cross section of 151 Pleuronectes platessa individuals. The novelty of this paper is checking the cellular homogeneity in the anterior, median and posterior sections of both ovaries from 15 fish, accompanied by a reading protocol to limit subjectivity during stereology readings. Once the ovarian structures were quantified for 151 individuals, a model was set up following the standardized staging grid of the International Council for the Exploration of the Sea (ICES), classifying each sampled individual into a maturity phase. These results showed that 23.4% of the time immature (A) individuals were correctly identified through the macroscopic method, but 47.9% of developing (B) individuals were classified under A, while individuals that had finished spawning were correctly identified as such 80.4% of the time. Finally, the maturity ogive and the length at which 50% of the population is sexually mature (L50) were calculated, with an L50 of 28.6 cm when using the macroscopic method and an L50 of 20.6 cm with the stereological method.