Genetic Structure and Diversity of Channel Catfish (Ictalurus punctatus) in Three Large Midwestern Rivers

Little information is available regarding the genetic structure and diversity of sportfishes in large rivers, which can be vital to continuing the sustainable exploitation of these fisheries. Additionally, impoundments often have vast impacts on riverine systems. These impacts include altering the flow regime, changing the nutrient load, and preventing migratory fish from reaching their spawning grounds. If fishes are prevented from reaching their spawning grounds, their genetic diversity and structuring could begin to change relative to historic measures, potentially decreasing their fitness and ability to survive. I screened microsatellite loci to assess the genetic population structure and diversity of channel catfish from four sites on the unimpounded Wabash River and two sites on the Ohio River, where there are lock and dams between the sites. Allelic richness ranged from 5.42 to 6.51, heterozygosity levels ranged from 0.650 to 0.712, and inbreeding coefficients showed signs of inbreeding and outbreeding (-0.115 to 0.063). Overall, 18 of 21 (85.7%) pairwise site comparisons of FST and Dest were significant. There was a significant positive relationship between genetic (FST and Dest) and geographic distance (FST: r=0.182, P=0.0344; Dest: r=0.182, P=0.0357). STRUCTURE analysis and PCA plots show strong defined structure for channel catfish, revealing three genetic clusters. I also assessed the genetic diversity and structure of channel catfish on the Illinois River, which is a highly impounded system. Allelic richness ranged from 2.76 to 3.75, heterozygosity levels ranged from 0.524 to 0.600, and inbreeding coefficients ranged from -0.071 to 0.081. I found a majority (14 of 21; 66.6%) of pairwise site FST tests were significant, yet I failed to detect strong patterns with STRUCTURE and PCA analysis. Additionally, FST values did not significantly correlate with river kilometer or number of dams between the two sites. Overall, I found no differences among sites with regards to genetic diversity and support for strong isolation by distance patterns of population structure in the Wabash and Ohio Rivers. As for the Illinois River, it seems that the impoundments may not affect genetic diversity, but are affecting genetic structuring. Results from this study indicate genetic drift is having a larger influence on channel catfish in the Illinois River than gene flow. This is the first study on channel catfish in the Midwestern US and provides important baseline data for their genetic diversity and structuring in the wild, and due to their commercial and recreational importance their status should continue to be monitored