Location: Warmwater Aquaculture Research Unit2013 Annual Report
1a. Objectives (from AD-416):
Determine effects of male:female ratio, stocking density, and post-spawning consolidation on spawning success in channel catfish.
1b. Approach (from AD-416):
This research will take place in 3 phases over 36 months, with each 12 month period being devoted to each of the 3 spawning trials. The first trial will determine the effects of male to female ratios of 1:1 and 1:4 on spawning success in channel catfish. Broodfish from a strain being developed as part of the USDA-ARS’s breeding program will be used in the study. Broodfish will be randomly assigned to treatments and stocked into 0.1 ha spawning ponds, with 6 replicate ponds per treatment. Ponds in both treatments will be stocked at approximately 1,100 kg/ha and the number of males and females in each pond will be adjusted to the proper sex ratio. The second trial will compare stocking rates of 1,100 and 2,200 kg/ha on reproductive success of channel catfish. At stocking brood fish will be randomly assigned to each treatment and stocked into 0.1 ha spawning ponds, with 6 replicate ponds per treatment at a sex ratio of 1:1 for both treatments. The third trial will determine effects of consolidating broodfish at end of the spawning season on spawning the following year. Fish from a large, unrelated spawning trial stocked at approximately 1,100 kg/ha will be used in this study. Fish from that trial will be harvested at the end of spawning (end of June) and a portion will be restocked at 2200 kg/ha (consolidated) and an additional portion will be restocked at 1,100 kg/ha (control). At stocking brood fish from each treatment will be stocked into 0.1 ha spawning ponds, with 6 replicate ponds per treatment at a sex ratio of 1:1 will be used for both treatments. In all trials, spawning cans will be placed in each pond on April 1 and cans will be checked for spawns through mid-July. Spawns will be taken to the hatchery, weighed, sampled to determine number of eggs, and placed in a hatching tank. At hatch, fry will be enumerated volumetrically and the percent hatch will be determined for each spawn. Treatments will be compared for number of spawns, weight of spawns, percent hatch, average date of spawn, and survival of broodfish. DNA markers will be used to determine parentage of spawns. Economic analysis will determine relative cost/benefits for treatments in each trial.
3. Progress Report:
Commercial catfish farming is the largest commercial aquaculture enterprise in the U.S. However, catfish production in the U.S. has decreased approximately 50% over the last 10 years due to increased production costs and competition from imported farmed catfish and pangasius. In order to remain competitive in a global market, U.S. catfish farmers must reduce production costs. Refinement of catfish broodfish management strategies could improve reproductive efficiency and reduce production costs. Currently most farmers use a 1:1 or 1:2 male to female stocking ratio in brood ponds. However, unpublished data from the Catfish Genetics Research Unit, in Stoneville, MS, USDA-ARS, has demonstrated that less than 10% of the males present account for over half the spawns, and about half of the males pond do not spawn at all. Therefore, commercial producers could possibly improve spawning efficiency by reducing the biomass of males in broodponds and replacing males with additional females. Costs of maintaining broodfish (feed, pond-space, etc.) would be similar regardless of sex ratio if the biomass was constant. Previous published data demonstrated no differences in the percent of females spawning at 1:1 and 1:4 male to female ratios, although study ponds were unreplicated. The objective of this study was to determine the effects of broodfish sex ratios on channel catfish spawning success and associated costs. Mature Delta Select strain channel catfish males and females (3 and 4 years old) were randomly stocked at about 1,000 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, 79º F, 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.