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)

the first reproductive cycle of 50 females of the shortfin silverside, chirostoma humboldtianum (valenciennes) in culture conditions was analyzed. ovarian developmental stages, gonadosomatic (gi) and hepatosomatic (hi) indexes were described. histo-logical description of the ovaries and quantification of estradiol serum levels (e2) and 17α-hydroxy-4-pregnen-3-one (17-p4) by radioinmune assay were performed. results showed a first 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-defined pattern of development. the gi and hi indexes values indicate a positive lineal relation to body-weight only during the reproductive season (r2 = 0.74 and r2 = 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 first 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/m l and 2.4 ± 0.3 ng/mlfor 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 first findings on the reproductive physiology of the shortfin silverside fish, suggesting an early steroidogenic activity in immature females. furthermore, the species maintains its hormona