Location: Warmwater Aquaculture Research Unit
Title: Seasonal Differences in Steroids and Maturation-related Genes in Channel Catfish Under Normal and Accelerated Thermoperiods Authors
Submitted to: Aquaculture America Conference
Publication Type: Abstract Only
Publication Acceptance Date: December 10, 2009
Publication Date: March 1, 2010
Citation: Small, B.C., Davis Jr, K.B. 2010. Seasonal Differences in Steroids and Maturation-related Genes in Channel Catfish Under Normal and Accelerated Thermoperiods. Aquaculture America Conference. In: Proceedings of Aquaculture 2010, March 1-5, 2010, San Diego, CA., Book of Abstracts CDROM, p927. Technical Abstract: Selective breeding of channel catfish, Ictalurus punctatus, is hampered by a long generation time. Female channel catfish typically spawn when they are 3-years-old; however, a low percentage of spawning may be observed at two years of age. Mature female channel catfish can spawn once annually. Their normal reproductive pattern is characterized by gonadal recrudescence that reaches a maximum in May with synchronous gonadal development and peak spawning in May and June. Factors which determine sexual maturation in catfish are not well understood, but such characteristics as age, size, and number of annual cycles are the most often mentioned features thought to influence the first reproductive period and spawning. These characteristics can be separated in catfish by altering the temperature cycles under which they are raised. Channel catfish held under a shortened annual temperature cycle of four months in 26°C water followed by two months in 13–14°C water spawned at a higher rate (73%) after three temperature cycles than fish held in outdoor ponds on two normal seasonal temperature cycles (10%). These data suggest that the onset of the maturation leading to spawning is a developmental event that requires three cycles of warm and cold periods. Fish from both treatment groups (Cycled and Control) were sacrificed for quantification of circulating estradiol concentrations and mRNA concentrations of gonadotropin subunits (GTH-a, GTH-Iß, and GTH-IIß) and steroidogenic factor-1 isoforms (SF-1a and SF-1b) in the pituitary and ovary. Among the measures of plasma steroid and tissue mRNA, only ovarian GTH-Iß mRNA was significantly different between the two groups of fish and was elevated during May in the 2-yr-old fish. In both groups of fish, measures of steroid and mRNA were lower in 2-yr-old fish relative to concentrations in 3-yr-old Control fish. In 3-yr-old Control fish, SF-1a, GTH-a, GTH-Iß, and GTH-IIß were all elevated in spring samples. Although considerable quantitative differences in the measured reproductive indices between 2- and 3-yr-old female channel catfish were observed, only GTH-Iß mRNA levels appeared to be indicative of higher spawning rates.