Most people who have spent any time in the Hagerman Valley are aware that catfish are commercially raised here. However, these fish are not native to the region but are imports transported from the east where many species of catfish live wild in rivers and lakes. Although now only present in Idaho because of human introduction, at one time the state once had a native species of catfish. This now extinct species, the western catfish, Ictalurus vespertinus, has been found as a fossil in many localities in the Glenns Ferry Formation that covers a large part of southwestern Idaho from Hagerman to Oregon.

The presence of the western catfish at a fossil site is often indicated by pieces of the pectoral spine, the bone that provides support to the front fin, and by individual vertebrae. Isolated bones of the skull are also often found but no complete skeletons are yet known. The pectoral spine is easy to identify by its long narrow sape and the small ridges along one edge. This gives the bone the appearance of a small jaw for which it is often mistaken.

Many species of wild catfish prefer rivers to lakes and this seems to have been the case for the western catfish. If one examines the sediments in which its bones are common, it quickly becomes apparent that its abundance is often related to sediment size, the coarser the sediments the more common catfish bones. Sediments in rivers tend to be coarse since the moving water moves finer particles downstream. When these finer particles reach the quiet water of a lake they settle to the bottom. The western catfish is uncommon in the finer sediments that are characteristic of lakes but its remains are common to abundant in fluvial (river) and floodplain deposits. Since some of the sediments that form the bluffs at Hagerman Fossil Beds National Monument were deposited in the river and floodplain part of the Glenns Ferry Formation, catfish is especially common at Hagerman localities.

Comparison of bones of the skeleton of the western catfish with living species indicates that it was a member of the bullhead group of catfish and is most closely related to the white catfish, Ictalurus cattus, and the spotted bullhead, Ictalurus serracanthus. The western catfish grew to substantial size and large individuals reached about half a meter (18 inches) in length, making it about 10% larger than its living relative, the white catfish. This would have made the western catfish a medium sized omnivore, scavenger and carnivore of the local fish fauna.

The western catfish survived in southern Idaho until about 1.8 million years ago and then became extinct. Today there are no native catfish west of the continental divide and all wild catfish are found to the east of the divide. Why did they disappear from the river systems of Idaho, but survive elsewhere? One possible answer is that 1.8 million years ago was the beginning of a climatic cooling that we know as an ice age. Perhaps the cooling climate and drop in water temperature caused the disappearance of the western catfish from Idaho river systems. Catfish are are sensitive to cold water temperatures and this limits where they can live. For example, channel cats need water between 75 and 85 degrees Fahrenheit to spawn while the brown bullhead will spawn in slightly cooler water around 70 degrees. If the water is too cold catfish will not spawn. An added problem is that if it takes too long for the water to warm enough for spawning, then the resulting juveniles will not grow large enough to make it through their first winter. Growth in fish is related to temperature and cooler water means slower growth. Today five different types of introduced catfish are present in Idaho; brown and black bullheads, blue catfish, flatheads and channel cats. A couple of species have established breeding populations but only in scattered stretches of the Snake River where the water is warm enough for spawning. Perhaps a similar ecological intolerance to cold water temperatures was the cause of the western catfish's extinction and its populations declined as areas with water warm enough for reproduction disappeared. At the moment we can't say for sure that this is the reason but it provides an interesting paleontological question that will require more research.