Native Aquatic Species of the Gila River Basin
in Arizona and New Mexico
Flathead Catfish (Pylodictis olivaris)
Flathead catfish were introduced into Arizona sometime prior to 1950 into the Gila River system, perhaps into San Carlos Reservoir, but possibly into the upper part of the drainage, in New Mexico, since they are now known from that area. The Colorado River populations in California and Arizona resulted, at least in part, from a stocking of about 600 flathead catfish above Imperial Dam made by the Arizona Game and Fish Department in 1962 (Fuller 2006). The natural range of this fish centers in the Mississippi River basin, and extends southeast and also southwest into coastal drainages to the Rio Grande River system (Minckley 1973).
Flathead catfish are mottled dark brown to yellow-brown on the back and sides. The head is broad and flat with small eyes. It has a large mouth with the lower jaw projecting beyond the upper jaw. The adipose fin is large and the tail is flat or slightly notched. Length varies between 12 to 52 inches, and flatheads can weigh between 1 and 65 pounds.
Flatheads are typically found in large rivers, where they live as adults in deeper pools near cover and are relatively sedentary. Adults move and feed mostly at night in clearer waters, but sometimes congregate below dams and feed voraciously throughout the day during spring floods and highly turbid water conditions (Minckley 1973).
Young flatheads (up to ten inches) eat insects and crayfish, switching to a fish diet as they grow older. Adults need a lot of fish to grow. To gain one pound, flatheads must eat about 10 pounds of live food (North Carolina State University 2002)!
Introductions of flathead catfish may be the most biologically harmful of all fish introductions in North America. Flatheads have been implicated in the decline of the federally threatened Gulf sturgeon by consuming young benthic fish in the Apalachicola River. In North Carolina, flathead catfish have been implicated in the decline of native sunfish and catfishes, which have experienced population declines where flatheads have been introduced. In Georgia, the flatheads may be eating the larval fish hosts that are needed to complete the life cycles of native freshwater mussels (TNC n.d.). High numbers of channel catfish and flathead catfish in the Salt and Verde Rivers may have limited the success of attempts to re-introduce the Colorado squawfish in the mid 1980s (Marsh and Brooks 1989). Reduction in local populations of channel and flathead catfish through commercial harvest, relaxed creel limits, and diversification of legal methods of capture were proposed as means to enhance the survival of re-introduced razorback suckers. It is thought that flathead catfish have led to the collapse of the native fish population in the Salt River upstream of the Roosevelt Diversion dam which in turn has led to the reduction in productivity of the threatened bald eagles breeding along the river.
Fuller, P. 2006. Pylodictis olivaris. USGS Nonindigenous Aquatic Species Database, Gainesville, FL; http://nas.er.usgs.gov.
Marsh, P.C., and J.L. Brooks. 1989. Predation by ictalurid catfishes as a deterrent to re-establishment of introduced razorback suckers. The Souhtwestern Naturalist 34:188-195.
Minckley, W.L. 1973. Fishes of Arizona. Phoenix, Arizona Game and Fish Department.
North Carolina State University. 2002. Flathead catfish poses risk to native North Carolina fish species. BulletinOnline.
The Nature Conservancy (TNC). N.d. Non-native invasive species in South Georgia. Joint publication with the Sapelo island National Estuarine Research Reserve.
June 25, 2009
Joseph J. Billerbeck - firstname.lastname@example.org