|Simco, Bill - BIO DEPT UNIV OF MEMPHIS|
Submitted to: North American Journal of Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 11, 2005
Publication Date: August 1, 2005
Citation: Davis Jr, K.B., Simco, B.A., Silverstein, J. 2005. Relationship of gonadal development to body size and plasma estrogen concentrations in channel catfish inctalurus punctatus. North American Journal of Aquaculture. 67:259-264. Interpretive Summary: Normal and hormonally sex-reversed females of the Marion strain and normal and sex-reversed fish of the USDA 103 strain were used to study the relative importance of body weight and plasma hormone concentrations in the development of ovaries in channel catfish entering their first and subsequent spawning periods. Body weight and plasma estrogen concentration were significantly correlated with gonadal development in two year old fish. In three-year-old fish only plasma estrogen was correlated with GSI and neither weight nor plasma estrogen correlated with GSI in four-year-old fish. No difference was apparent between normal and sex-reversed females. Plasma estrogen was thought to be a more reliable estimate of gonadal development, however, estrogen in the feed increased plasma estrogen concentration without an increase in gonadal development.
Technical Abstract: Four-year-old channel catfish females from the Marion strain and two- and three-year-old females from the USDA 103 strain were used to correlate body weight and plasma sex hormone concentrations with gonadal development. A higher percentage of USDA 103 females are known to spawn at 2 years of age than other strains, including the Marion strain. The four-year-old Marion females weighed from 3000 to 4500 g and all had a gonadosomatic index (GSI) above 9. Two-year-old USDA 103 females ranged from 436 to 884 g and had a GSIs which ranged from 0.34 to 6.64. A population of two-year-old USDA 103 fish that had been hormonally sex- reversed to females (USDA SR103) weighed from 400 to 1400 g and had GSIs from 1 to 10. Three-year-old USDA SR103 females weighed from 1300 to 2800 g and had GSIs from 2 to 14. Only about 10% of the two-year-old USDA SR103 females had GSI values similar to fish expected to spawn. Body size was significantly correlated with GSI in two-year-old USDA 103 and USDA SR103 females, but not in three-year-old USDA SR103 fish; plasma estrogen was highly correlated with GSI in fish of both ages. Plasma estrogen concentration was a more reliable predictor of GSI than body weight. Neither body weight nor plasma estrogen concentration were correlated with GSI in the four-year-old Marion strain females which all had mature ovaries. Plasma estrogen, testosterone and GSI were markedly lower in two-year-old fish than in three-year-old fish in both populations of USDA females. Oral administration of estrogen to two-year-old 103 females increased plasma estrogen but did not increase ovarian development.