## 3 Results
### Histological Analysis  
The sex ratio of 120 individuals in the study was balanced: 46 females (38.4%), 50 males (41.6%), and 24 (20%) undetermined individuals. The frequencies of oocyte diameter throughout the year are shown in Figure 3. By measuring the diameter of oocytes, we determined that the largest recorded diameter was in September, at 98.17 \(\upmu\)m, while the average largest diameter of oocytes was in July, at 17.12 \(\pm\) 27.08 \(\upmu\)m. The smallest average values were recorded in March, at 3.92 \(\pm\) 0.94 \(\upmu\)m. One-way ANOVA showed differences in oocyte size through months (F = 8.7001, \(p\) < 0.001), and subsequent Fisher LSD post-hoc analysis revealed several phases in oocyte development throughout the yearly cycle. The first statistically different oocyte size was noted during March and April, indicating intensive early gametogenesis and oocyte growth, while the second phase, noted during July and August, is probably the peak of development and the oocyte maturation phase. The third phase, as revealed by post-hoc analysis, is the degenerative oocyte stage at the end of the year (November through December). We initiated research on gonad development in March, when the sample consisted of eight individuals whose sex could not be determined, and only two females in early developmental stages (Figure 4A). Primary oocytes predominate in the ovaries. April is the month when our gonad sampling results show progress in sexual development, with two females in an advanced stage of sexual development with vitellogenic oocytes (Figure 4C), four in the initial stage (Figure 4A), and two males in an early developmental stage (Figure 4B). The sex could not be identified in two individuals. May is characterized by further progress in individual sexual maturation, with no individuals whose sex could not be determined. In May, the analysis of qualitative stages of gonad maturation showed, as depicted in Figure 5, that females were in an advanced stage (65%), and males were ready for spawning (50%). Males are ready for spawning from May to March (10 months), but this number and percentage decrease as the spawning season progresses and sea temperature decreases (Figure 5). In June, four females (65%) and four males (100%) were recorded in the spawning stage, and there were no individuals whose sex could not be determined (Figures 4E,F and 5). July, August, and September are months in which we record males in the spawning stage and females in the spawning stage or high maturity stage. In these months, two individuals could not be determined by sex or all were defined as is the case in September. In October, along with individuals in a high stage of maturity and in the spawning stage, we first recorded two males in the post-spawning stage. In November, we first found a female in the post-spawning stage and more males in this stage (20%). Other than females in the spawning stage, December is characterized by a smaller number of males in spawning, only two, and two individuals whose sex could not be determined. January and February are characterized by a larger number of individuals in lower degrees of sexual maturity or in a resting stage, as well as a larger number of individuals whose sex