Epalzeorhynchos frenatus, the Bridled Shark-Minnow
Epalzeorhynchos frenatus (Bridled Shark-Minnow or "Rainbow Shark"). "Rainbow Shark" is now the slightly-too-ambitious novelty name for this handsome fish. Though since the 1980s we have stopped calling it by its old name "Labeo," which refers to an African genus, it's a shame we can't just translate its specific name, to call it the "Bridled" Shark-Minnow. The bridle, of course, refers to the black line across the mouth. The sleek torpedo-shaped body is a deep gunmetal gray to olive-brown, countershaded to a paler belly, with a dark smudge in the caudal peduncle. Though I couldn't justify "rainbow," the best form, which used to be called erythrurus ("the red one"), shows in its fins a very strong and clean red, when it's in good health. The color can be brighter than the brick color of more ordinary specimens, and in the tailfin it almost reaches a lacquer scarlet. When the red shades to black at the trailing edge of the anal fin and in the ventral fins, the fish is male, according to Gunther Sterba, Freshwater Fishes of the World, 1966, p265. If this is true, then could we reduce friction by keeping one male and two females? And reducing friction is an issue with this desirable fish, I'm sorry to say.
I think E. frenatus is one of the most elegant Cyprinids. More often than not, though, the version I'm seeing in the LFS is a perfectly unnecessary albino mutant. Pretty enough, I suppose, if you like that sort of thing.
Epalzeorhynchos frenatus come from the upper Mekong catchment, where the great river forms northern Thailand's border with Laos. They enjoy some fast-flowing current, and they'll sometimes leap up the filter outflow, like a salmon in the fish ladder of a dam, and wind up in your h.o.t. filterbox. From which they'll escape to the floor, for all these shark-minnows are built for strenuous athletics. E. frenatus will be more comfortable at temperatures around 74-77o F than at the steamy tropical heat we usually like to apply, and cooler temperatures may help cool some of their hyperactivity. In their home waters they rasp at the biofilm, without getting the kind of algae-eating credit that goes to Siamese Algae Eaters, and they relish a pretty constant supplement of spinach and other greens, as well as sinking spirulina wafers.
There are five described species of Epalzeorhynchos. E. munense, named for the Mun River, a tributary of the Mekong, is so similar as to be easily confused. The sister genus is Crossocheilus. The genus Epalzeorhynchos is distinguished from others in its species group by a unique movable sensory rostral lobe encased in a wide groove beneath the lachrymal bone; the lobe is an elongate structure with a conical tubercle at its tip and a series of papillae or tubercles along its lower edge.
Breeding just doesn't happen in home aquaria, which is a pity. The fish is bred in pools in Singapore and Bangkok. I understand that hormone injections are used, to bring these fish into breeding condition. Partly because of its slightly cooler temperature requirements, E. frenatus was one of the handful of fishes investigated when the University of Hawaii's Center for Tropical and Sub-tropical Aquaculture was researching ways to help the expansion of the fledgling Hawaiian tropical fish farming industry, in 1996-98. They reported that sexual maturity ("gonad maturation") dropped sharply in October-November and didn't pick up again till March. The researchers attributed this to a discrete spawning season, triggered not only by cooler temperatures, but by changing day-length. Even if you might be tempted to discount day-length as unimportant in a fish that is found at 20o North latitude— still within the tropics— this finding might offer a clue to unlocking the fishes' intractable breeding behavior. (The report was deleted unfortunately when the CTSA shifted to its new site.)
At small sizes the Bridled Shark-Minnow already flirts about in strenuous competition with others of its species, and even chases barbs up and down through the undergrowth. As it matures this fish gets increasingly territorial and jealous, like most of its Epalzeorhynchos kin, but maybe not to the same extent as E. bicolor, the Red-Tailed Black Shark. If you have a community aquarium that is 30 gals. or larger, and if you have wisely broken up its volume into complicated territories, defined by bold dense plantings and shadows, with plenty of hiding spots under ledges, or in hollow logs and under roots, you should try to keep three of these fine under-rated fishes. The trick is to give each a home territory from which it can't see the others. Don't try to keep just two in the same aquarium, because they will be instant rivals who will focus all their energy on battling each other. A third player, however, breaks up the game. You'll need to find three at one time that are well matched in size; one who is only slightly smaller will get the worst of the coming encounters. Introduce them all at one time, in their separate travelling bags, for if you give one fish just 24 hours head start to stake out a turf, the odds will be weighted in its favor forever. A trio of sparring opponents set up like this worked out well for me, til, after a year or so, one died. After that, the remaining two focused so roughly on each other's intrusive presence that they had to be separated. Was this partly that they were approaching sexual maturity? Still, this is not a dependable community fish. What a shame!
Links. See some of the varied experiences people have had with it at the Age of Aquariums.
Epalzeorhynchos frenatus at Fishbase. E. munense (using the same photo) at FishBase.
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