THE JOURNAL OF EXPERIMENTAL ZOOLOGY 298 : 60-66 (2003) . Oogenesis and Plasma Levels of Sex Steroids in Cultured Females of Brown Trout (Salmo trutta
Linnaeus, 1758) in Chile. FRANCISCO ESTAY,1* ANDRÉS DÍAZ,2 RODRIGO PEDRAZZA AND NELSON COLIHUEQUE3
1.- Piscicultura Huililco Ltda., Pucón, Chile.
2.- Reproduction Biology Laboratory; INTA, University of Chile, Santiago, Chile
3.- Departamento de Ciencias Básicas, Universidad de Los Lagos, Osorno, Chile
Naturalized brown trout populations in Chile are a valuable genetic resource with aquaculture potential. The oogenesis of a three-year-old brown trout cultured population was studied in southern
Chile. Gonadosomatic index (GSI), oocyte growth, gonadal microscopic characteristics and plasma levels of estradiol-17? (E2), testosterone (T), and 17?-hydroxyprogesterone (17?-HP) were measured
bimonthly for a 9 month period before spawning. The maximum GSI level (22 %) was similar to that described for other salmonids, although it was reached in May, more than one month before the
population started spawning. Oocyte growth increases strongly from January when diameter reaches more than 1 mm. The vitellogenic period (6-7 months) is consistent with the long vitellogenesis,
described for salmonid females maturing at three years old. E2 shows a slow increase from November, reaching its peak value in March (65.2 ± 0.7 ng/ml), during maximal vitellogenic activity. T
increases as oogenesis progresses, reaching a maximum of 90 ± 20 ng/ml during May, and falling considerably during ovulation. Following a typical pattern of progestogens in salmonid oogenesis,
17?-HP stays at basal levels during most of oogenesis, but experiences a strong surge (2.0 ± 0.4 ng/ml) just before ovulation.