Location: Warmwater Aquaculture Research Unit
2013 Annual Report
Mature Delta Select strain channel catfish males and females (3 and 4 years old) were randomly stocked at about 1000 lbs per acre in 0.25 acre ponds during the last week of Febuary 2012. Broodfish had been previously individually marked with pittags and sampled for DNA to be used for subsequent parentage determination. Two sex ratios were compared: a 1:1 male to female ratio (30 males and 30 females per pond) and a 1:4 male to female ratio (12 males and 48 females per pond) with six replicate ponds per treatment. Spawning cans were placed in ponds the second week of March at a rate of 2 cans for every 3 males (8 cans in the 1:4 ponds and 20 cans in the 1:1 ponds). One week after placing spawning cans in ponds, they were checked 2 to 3 times per week for spawns through mid-July. Spawns were removed, brought to the hatchery, and weighed. A sample of eggs was taken from each spawn, weighed and counted, and the counts were used to determine total eggs per spawn. Each spawn was hatched in a separate 20 gallon fiberglass tank provided with flow through ground water (1 gal/min, 79ºF, 5 ppm D.O.). Eggs were treated with hydrogen peroxide once daily until the eyed stage. Sac fry were siphoned into a volumetric cylinder and number of fry was determined volumetrically. Ten to twenty fry were sampled from each spawn, preserved in ethanol, and used for DNA isolation for parentage determination. Parents and fry were genotyped for 2, multiplexed DNA microsatellite panels to determine the individual male and female parent of each spawn. Details of protocols used for parentage determination are given by ARS scientists. In August 2012, ponds were seined and drained and remaining fish were counted and pittags were recorded to allow determination of broodfish survival. At the time of this report, DNA determination of parentage was still underway, therefore we do not present data on individual female and males spawning success. We assumed each spawn was produced by a single female in estimates of female spawning percentage. Information on individual spawning success and number of spawns produced by individual male and female broodfish will be included in the final report when the parentage analysis is complete. The broodfish sex ratios were compared by ANOVA for broodfish survival, percent of females spawning, spawning day (the first day a spawn was collected was defined as day 1 and all susbesquent spawn dates were determined relative to day 1), spawn weight, percent hatch, number of spawns per acre of broodfish pond, weight of eggs per acre, number of eggs, per acre and number of fry per acre.
Reproductive traits for 1:1 and 1:4 male to female channel catfish broodfish treatments are summarized. Male broodfish had lower survival than female broodfish (65.5 vs 91.4%) but there was no effect of sex ratio on survival of males or females. Spawning date, spawn weight, and percent hatch were not affected by broodfish sex ratio. Percent of females spawning was over 3 fold higher for the 1:1 male to female ratio compared to 1:4 (57.2% vs. 16.3%). The much higher percentage of females spawning at 1:1 male to female ratio resulted in the 1:1 ratio being superior to 1:4 even when reproductive traits were considered on a per acre basis. Relative to the 1:4 ration, 1:1 resulted in more spawns per acre, greater weight and number of eggs produced per acre, and greater number of fry per acre.
The results demonstrate that a greater percentage of channel catfish females spawned at a 1:1 male to female broodfish ratio than at a 1:4 male to female ratio. The differences in female spawning percentage was large enough that the 1:1 male to female ratio was superior to the 1:4 ratio even when reproductive output was considered on a per acre basis. The increased number of females per acre in the 1:4 ratio ponds would have had an advantage on a per acre basis if the percent of females spawning had been similar in the two treatments. Therefore, the results of this study indicate the reproductive efficiency and economics of channel catfish fry production at a 1:1 male to female broodfish ratio are superior to a 1:4 male to female ratio.