By Howie Galoff in collaboration with Guy Bagley
Commonly known as the "Plains Killifish" (undoubtedly referring to its native habitat - the Great Plains), we acquired a North American native killifish at the 2003 AKA National Convention that is anything but plain. Entered as Plancterus zebrinus Double Mountain Fork Brazos River Rule, TX, most people would probably be more familiar with the nomenclature: Fundulus zebrinus. While researching this article, I discovered that plancterus is/was a subgenus of fundulus but I was unable to ascertain if it has been elevated to full genus status by taxonomists or if the entrant was simply providing specific taxonomic information.
This fish is found in Montana and South Dakota, eastward to Missouri, and in Nebraska, Wyoming, Colorado, Kansas, Oklahoma, New Mexico and Texas. It inhabits shallow streams, usually over a gravel or sand substrate, and tolerates extreme alkalinity and salinity where few other fishes can survive. It inhabits the drainage systems of the Brazos, Colorado, Trinity, Rio Grande del Norte, Pecos, Missiouri and Platte Rivers, but was not native to all these locations - having been introduced from bait bucket releases or accidentally stocked as contaminants with other species. The fish is reported to bury itself in sand with only its eyes and mouth visible. This behavior may protect the fish from stream desiccation and/or extreme sunlight, and may help in detecting potential prey while avoiding predators.
Adult Fundulus zebrinus attain a length of 3-4" with the females generally being slightly smaller than the males and have a maximum reported lifespan of 3 years. The female's body is gray-brown to dark olive with 15-20 short, narrow, dark gray to almost black cross-bars on the sides with all the fins being pale gray to colorless. The background color of the male's body is dark olive and the sides have 14-20 silver to white cross-bars. In breeding males the intervening zones between the light bars become almost black and they develop a pink or red hue over the lower parts of the sides while the abdominal regions and throat become red. Most descriptions state the unpaired fins are dark gray with a red margin or a red submarginal band followed by a narrow pale gray margin. The fish we acquired, however, have a gray caudal and the dorsal and anal fins have a rather broad gray margin around an area of reddish-orange. The paired fins (pectoral and ventral) are almost totally this reddish-orange color with possibly the narrowest of gray margins. It is recommended that the fish be kept in a large aquarium containing hard or slightly brackish water with a sand or gravel substrate and that aquatic plants be provided as a spawning medium and to provide females with areas to hide from the males, which reportedly can be aggressive. We were told the fish do best in cool water.
Zebrinus contd .
Equipped with the above information, we set up a 20 gallon unheated tank. Over the undergravel filter plate we placed 1-2" of gravel and pebbles. We filled the tank with aged tapwater (hardness: 385 ppm and pH: 7.8) to which we added sea salt mix at the rate of 1 tablespoon/5 gallons. Included in the aquascaping were several Amazon swords and some hornwort. A powerhead was affixed to the lift tube of the undergravel filter and the venturi was adjusted to provide aeration. A floating mop, which extended the full depth of the tank, was introduced not only for spawning but to provide an additional hiding place for the female. The pair was fed a variety of live food. We diligently checked the mop and found an occasional egg, which we water incubated - hatching generally occurred in 10-12 days. The fry accepted Artemia nauplii immediately. Unfortunately, we lost our initial group of fry when the tank crashed. Rarely we would see fry in with the parents but their existence was short-lived. I believe they became a meal for the adults. I was reluctant to take the pair to the MKKA show without having progeny at home, but we felt the fish deserved to be displayed so others could appreciate their beauty.
And now, the reason for the title of this article. Upon returning home from the MKKA show, we found the zebrinus tank teeming with fry. We immediately set up a new home for the parents and within a matter of days, there were over 200 fry in the original tank. Apparently, the fish scatter their eggs with many more ending up in the substrate than in a mop. Perhaps the eggs found protection in crevasses or by being indistinguishable from the gravel - or maybe the adults don't forage for roe. Whatever the reason, the eggs avoided detection and hatched in an environment devoid of predators. Raising the fry has been straightforward and nonproblematic. I suspect they would readily adapt to flake food but have not tested this assumption. Growth has been steady and they are beginning to sex out (at 5 months). The literature states sexual maturity is not reached before an age of 8-12 months. Of incidental interest, another author states the eggs go dormant if the pools of water in which that were deposited dry up and hatch when the pools refill.
In conclusion, our success with this stunning fish has truly been serendipity
"a desirable discovery - made by accident."