THE JOURNAL OF EXPERIMENTAL ZOOLOGY 280:429-438 (1998) 
Gametogenesis and Sex Steroid Profiles in Cultured Coho Salmon (Oncorhynchus kisutch, Walbaum) 

FRANCISCO ESTAY1, ROBERTO NEIRA2, NELSON F. DIAZ1, LUIS VALLADARES3, AND ALFREDO TORRE

1.- Faculty of Sciencies, University of Chile, Santiago, Chile
2.- Faculty of Agricultural and Forestry Sciences, University of Chile, Santiago, Chile 
3.- Reproduction Biology Unit, INTA, University of Chile, Santiago, Chile 
4.- Fish Culture Center, IFOP, Coyhaique, Chile 

Abstract

The gametogenesis of a 2-year-old coho salmon broodstock population cultured in a fish farm in southern Chile was studied. Gonadosomatic index (GSI), microscopic gonadal traits, and serum levels of estradiol-17ß(E2), testosterone, and 17alfa,20ß-dihydroxy-4-pregnene-3-one (17,20P) in both sexes were recorded beginning 9 months before spawning in bimonthly samplings. Maximum GSI means were reached during May, the month of spawning, with 16.8 ± 4.1% for females and 8.4 ± 0.8% for males, both values wíthin the range describes in the literatura. GSI in males, however, was triple that of females during January., showing a faster rate of gonadal growth in males in early summer. Gonadal microscopy for both sexes showed stages correspondinto those describes by different authors for other salmonids such as rainbow trout. The secondarv vitellogenesis period was 4 to 5 months and corresponded with the short vitellogeniesis model describes in rainbow trout for broodstocks maturíng at 2 years of age. The serum profiles of sex steroids in both sexes are consistent with those describes in coho salmon and other salmonid species. In females, E2 and 17,20P show opposite profiles, reaching their maximum levels (E2: 45.13 ± 11.3 ng/ml; 17,20P: 24.47 ± 7.34 ng/ml) during vitellogenesis (March) and ovulation (May), respectively. In both sexes, testosterone concentration shows maximum levels in May (females: 61.68 ± 15.75 ng/mi; males; 107.8 ± 11.6 ng/ml), suggesting the physiological importance of this hormone during maturation, either directlv or as a substrate for the svnthesis of other hormones. In males, the maximum level of 17,20P (22.33 ± 4.5 ng/ml) also occurs in Mav during total spermiation, which confirms its role in semen production and semen fluid regulation as describes in the literatura about this hormone in salmonid males. On the basis of the data obtained, a reproductive pattern is proposed for 2-year-old salmon cultured in southern Chile. J. Exp. Zool. 280:429-438, 1998. ©1998 Wiley-Liss, Inc.