Differential Seasonal Steroid and Gonadotropin Expression in Full-Sibling Female Channel Catfish Maturing at Two or Three Years of Age under Normal and Accelerated Thermoperiods

The present study was designed to determine whether female Channel Catfish Ictalurus punctatus exhibiting accelerated maturation display similar steroid (estradiol and testosterone) and gonadotropin (luteinizing hormone and follicle-stimulating hormone [FSH] messenger RNA) profiles within the first reproductive period compared with full-sibling females that reached maturity 1 year later. The accelerated maturation (AM) fish were maintained under a shortened annual temperature cycle, consisting of 4 months in 26 degrees C water followed by 2 months at 13-14 degrees C, repeated for three cycles. In 2007, 2-year-old AM fish were 12 times more likely to spawn on any given day than the normal maturation (NM) fish. The 2-year-old NM group was 21 times more likely to spawn as 3-year-old fish in 2008 than in the previous year, 2007. In 2007, NM fish had higher body mass in January, March, and May and maintained higher gonadosomatic index (GSI). Two-year-old AM fish never had significantly higher levels of any measured variable than did 2-year-old NM fish. Compared with NM fish (2007), 3-year-old AM fish (2008) in their first reproductive period had significantly higher GSI, body mass, estradiol, and testosterone. The high spawning success of 2-year-old AM fish was not indicative of seasonal steroid and gonadotropin profiles relative to 3-year-old cohorts reared under standard conditions. However, seasonal levels during the first reproductive period of AM fish (2 years of age) were well below those of mature NM fish (3 years of age). The low plasma sex steroids and pituitary FSH and LH messenger RNA expression in fish undergoing accelerated maturation is perhaps the most interesting result of this study, since levels were sufficient enough to result in increased GSI and greater than 70% spawning success in these fish.