A Hunt for the Red River Pupfish

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Vince Brach

Freshwater and Marine Aquarium: December 1996

Even though I've logged more than 35 years of native fish collecting, I have to confess that my "hunts" are still a little like the game of backgammon: skill helps, but a good dose of luck is essential for success. Happily, in this column I'm going to tell the story of a "perfect" collecting trip where everything went as expected. I found the sought-after fish in abundance, exactly where they should be, along with another desirable species that I collected with no additional effort. Best of all, almost all of them survived the trip home and are flourishing in captivity. It just doesn't get any better than this! In the last Dipnetter I told you about that beautiful little bully known as the sheepshead minnow, Cyprinodon variegatus. This gorgeous topminnow, with its iridescent blue napes and yellow pectoral and anal fins, tolerates an astonishing range of salinity--probably as great a range as any North American fish. However, almost all species in this genus seem to prefer at least some salt, and most prefer distinctly brackish water. Not surprisingly, accidentally introduced populations of sheepshead minnows are established only in a number of permanently saline Trans-Pecos and San Antonio Basin waters in Texas (Hubbs et al., 1991). Many biologists believe that with the recession of the Eocene shoreline eastward across the Gulf region, some naturally stranded populations of C. variegatus or a closely related species found themselves in hospitably saline waters. These fish subsequently evolved into the many distinct species of pupfish, such as the Comanche Springs (C. elegans), Pecos (C. pecosensis) and Conchos pupfishes (C. eximius) found in Texas and Mexico. While many of these species are threatened or even endangered today (and must never be collected without a permit, and then very sparingly), one--the Red River pupfish, Cyprinodon rubrofluviatilis--is common in portions of the Red, Brazos, Canadian and Colorado River basins in Texas. It was this handsome little fish that became the object of my search.

In planning my expedition, I noticed that although the Red River forms the border between Texas and Oklahoma from the Texas Panhandle to Arkansas, range maps of the Red River pupfish show that it only occurs as far east (approximately) as Wichita Falls. On a geologic map, this range corresponds to the furthest extent of the Leonard group (Permian) red clay and sandstone formations on the surface. These formations harbor large amounts of gypsum and salt from the evaporation of the ancient Permian seas. Water trickling through this formation becomes quite brackish--so much so that the salty water poses a corrosion threat for pumps and other machinery, especially during drought.

Traveling from my home in Tyler, Texas to the Wichita Falls area along Texas Highway 82 in late June, I stopped at almost every creek crossing on the highway from Saint Jo westward to sample for C. rubrofluviatilis. All collections were disappointingly negative for this species (and the water was quite fresh to my taste) until I spotted a tiny creek threading its way through brick-red Permian sandstone on the north side of Burburnett, Texas northwest of Wichita Falls. Climbing down to the water, I noted rank streamside growths of tamarisk or salt-cedar (Tamarix gallica L.), a naturalized exotic shrub with a strong preference for saline environments. My hopes began to rise, since on the Texas coast this shrub, which grows to the size of a small tree, serves as a good indicator of sheepshead minnow and sailfin molly (Poecilia latipinnis) habitat.

The water of the tiny creek was almost as salty as seawater, measuring 1.018 specific gravity on my field hydrometer. Although only a few tens of centimeters deep at its greatest depth, I saw groups of Red River pupfish darting back and forth over the reddish gravel as I approached. A sweep of the dip net yielded half a dozen pupfishes or more, often along with several plains killifishes (Fundulus zebrinus)--the second of the two species I had hoped to find. However, other than a very occasional mosquitofish (Gambusia affinis), I took no other fish from the site.

Cyprinodon rubrofluviatilis is smaller and somewhat less stocky than C. variegatus. Its field guide illustrations do not do it justice. In my opinion, breeding C. rubrofluviatilis males are even handsomer than those of C. variegatus. The nape flashes brightly iridescent purplish blue with hints of green along the upper flanks, while the lower face and ventral region forward to the anal fin glows with a mottled yellowish gold. As with many other fishes, diffraction produces the blue and green iridescent colors. These colors are strongly influenced by the direction of light, becoming almost invisible when the fish is viewed from above.

Most of the specimens I collected on this trip were rather small (under 10 mm), indicating early spring spawning. Similarly, the specimens of F. zebrinus were mostly small young of the year, with only a few 50mm specimens showing the salmon-tinged anal fins of breeding males. Females of both species are duller, but several juvenile male C. rubrofluviatilis showed surprising traces of breeding colors even while quite small. Almost all of the collected specimens survived the two-day trip home in insulated buckets aerated by battery-driven bait bucket bubblers. Upon arrival, I housed a dozen of my captives in a blasting sand-bottom 10-gallon tank filled with 1.018 s.g. diluted seawater and decorated with sandstone slabs taken from the collection site. Over a period of one week, I added seasoned fresh water to the tank until the specific gravity measured 1.010. This concentration greatly reduces the amount of annoying salt creep without adversely affecting the fish.

In captivity, the Red River pupfish proved even more aggressive and territorial than the sheepshead minnow. The largest male, a 25mm specimen in full breeding colors, quickly dominated the tank and spent most of its time chasing the other fish, although the chases were usually short and apparently harmless. Curiously, the unrelated F. zebrinus housed with them showed much of the same aggressive behavior, although this species tends to spend more of its time at the surface. All of the fish took commercial flake food within hours of capture and are doing well at the time of writing.

Fish collecting in new territory is so often heavy on effort and short on results that it seems extra-special when all of the planning and preparation pays off, as it did on this trip. I hope that your enjoyment on your next dipnetting expedition approaches what mine has been on this one--you'll count it as one of the most memorable trips of your life!

References:
Hubbs, C., R. J. Edwards, and Gary P. Garrett. 1991. An annotated checklist of the freshwater fishes of Texas, with keys to identification of species. Texas Journal of Science 43(4): 1-56.