Desarrollo ovárico y su relación con las concentraciones séricas de 17β-estradiol y 17α-hidroxi- 4-pregnen-3-ona en hembras de primera maduración de pez blanco, Chirostoma humboldtianum (Atheriniformes: Atherinopsidae) Association between ovarian development and serum concentrations of 17β-estradiol and 17α-hydroxy-4- pregnen-3-one in fimaturation females of the shortfi n silverside fi sh, Chirostoma humboldtianum (Atheriniformes: Atherinopsidae)

The fi rst reproductive cycle of 50 females of the shortfi n silverside, Chirostoma humboldtianum (Valenciennes) in culture conditions was analyzed. Ovarian developmental stages, gonadosomatic (GI) and hepatosomatic (HI) indexes were described. Histological description of the ovaries and quantifi cation of estradiol serum levels (E2) and 17α-hydroxy‐4‐pregnen-3-one (17-P4) by radioinmune assay were performed. Results showed a fi rst reproductive season longer than six months. Females initiated spawning at the age of one year. Four ovarian maturation stages (I to IV) were determined during the spawning season and one (V) during the non-spawning season, the last one showed a non-defi ned pattern of development. The GI and HI indexes values indicate a positive lineal relation to body-weight only during the reproductive season (r 2 = 0.74 and r 2 = 0.86, P ≤ 0.05, respectively). Histological analysis of the ovaries indicated that the species correspond to the pattern described as group-synchronous with multiple spawnings. The follicular population showed reproductive activity during the fi rst stages of maturation with a predominant population of pre-vitellogenic follicles. As the ovarian maturation increased, the presence of all the follicular developmental stages was observed, with a tendency of an increase of vitellogenic and mature follicles. The concentration of circulating sexual steroid hormones of estradiol (E2) and 17α-hydroxy-4-pregnen-3-one (17-P4) were high during stage I (2.5 ± 0.7 ng/mL and 2.4 ± 0.3 ng/mL for E2 and 17-P4, respectively); a decrease was observed during stage II, and the highest values were observed in stage IV (7.6 ± 2.1 ng/mL for E2 and 1.8 ± 0.9 ng/mL for 17-P4). The same pattern was observed during non-spawning season (ANOVA P < 0.05), these results are the fi rst fi ndings on the reproductive physiology of the shortfi n silverside fi sh, suggesting an early steroidogenic activity in immature females. Furthermore, the species maintains its hormonal capacity during the post-spawning season, as it is supported by their follicular composition. The aforementioned will allow to have a better understanding of the mechanisms involved in their reproductive processes and to improve the mechanisms utilized to control their reproduction and for the production of eggs and larvae in culture conditions.