Frequency of Opercular Deformities in Age‐0 Native Catostomids in the San Juan River from 1998 to 2012

Abstract

AbstractIn the San Juan River, the recruitment of early ontogenetic stages of federally endangered Razorback Sucker Xyrauchen texanus to subadult or adult stages is rare. Opercular deformities have been detected in larval and early juvenile Razorback Suckers in the San Juan River and were investigated as an impediment to recovery of the species. Larval and early juvenile (age‐0) native San Juan River catostomids taken from 1998 to 2012 were examined for presence of opercular deformities. The frequency and severity of opercular deformities in Razorback Suckers were compared with opercular deformities in Bluehead Sucker Catostomus discobolus and Flannelmouth Sucker Catostomus latipinnis and with hatchery‐produced Razorback Suckers. Deformities were primarily observed in larval stages and occurred both unilaterally and bilaterally. Opercular deformities were relatively consistent among years for all three species. The frequency of opercular deformities in Razorback Suckers was more than three times higher than in Bluehead Suckers and more than five times higher than in Flannelmouth Suckers. Opercular deformities in all species were high when compared with Razorback Sucker brood stock and with wild fish in other river basins. This high rate of deformity in larvae and early juvenile San Juan River Razorback Suckers likely increases mortality and inhibits recruitment to later life stages.