2010 Annual Report
1a.Objectives (from AD-416)
Determine steroid levels in reproductive catfish to determine early signs of reproductive success. Evaluate the use of ultrasound estimation of ovary size, level of plasma steroids, group/family of origin, and body weight as predictors of incidence and timing of pond spawning of 2 and 3 year old channel catfish. Evaluate use of ultrasound imaging to sort female channel catfish broodfish on commercial farms into two groups based on estimated ovary size (large vs. small ovaries), and compare steroid levels and incidence and time of spawning of these two groups. Determine the influence of chemical, biological and environmental factors on channel catfish respiration, growth and production, and develop and test practical management methods to minimize limits on production. Induce early maturation in channel catfish.
1b.Approach (from AD-416)
Catfish blood will be analyzed for steroid levels using HPLC/MS. Ultrasound images of female channel catfish ovaries and plasma steroid hormone levels of male and female channel catfish will be collected prior to the spawning season. Fish will be allowed to mate at random in spawning ponds and parentage of spawns will be determined via molecular markers. Statistical analysis will be conducted to determine if ultrasound imaging or steroid hormone levels are predictive of spawning time and incidence. Female channel catfish will be sorted based on ultrasound image predicted ovary size on commercial catfish farms to determine if ultrasound image of ovary size can be used to predict spawning success of females on commercial catfish farms. Ten standard hatchery troughs will be operated during the 2008 spawning season. Spawns will be weighed and sampled prior to being placed in the incubator, and the number of sac fry produced from each trough will be determined, allowing for a calculation of hatch rate. A similar number of troughs will be operated and sampled using the traditional method. Water flow rates, dissolved oxygen concentrations, and water temperature will be monitored. Fish will be exposed to different environmental temperature regimes.
Pond spawning incidence and time were determined for 2 and 3 years old channel catfish from a composite population derived from 10 commercial farms. Parentage of offspring was assigned by DNA markers inheritance. Spawning time differed between farms and differences between farms were consistent for 2 and 3 year old fish. Spawning time was positively correlated for females across years. Data suggest genetic variation for spawning date and the possibility for altering spawning date through selection for females. Farm or origin had no effect on spawning incidence for males or females, and spawning success as 2 year old fish was not related to spawning success as 3 year olds. Less than 15% of males were responsible for ~ 65% of spawns. Spawning time of males is difficult to interpret because males spawn multiple times over a season. Spawning females were larger than non-spawning females as 2 year olds, but spawning and non-spawning females were not different in size as 3 year olds. Spawning males and non-spawning males were not different in size as 2 year olds, but as 3 year olds spawning males were larger than non-spawning males. Spring serum levels of estrogen and testosterone and ultrasound images of ovarian development were not predictive of spawning incidence or time in 2 or 3 year old females.
Factors determining sexual maturation in catfish are poorly understood, but age, size, and number of annual cycles are thought to influence the first reproductive period and spawning. Influence of age, size and number of annual cycles on maturity were determined for catfish by temperature cycle manipulation. Fish exposed to 3 shortened annual temperature cycles were compared to fish exposed to two normal annual cycles. 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 were examined. Although differences in the measured reproductive indices between 2- and 3-yr-old female channel catfish were observed, only GTH-Iß mRNA levels was related to spawning incidence.