Dianema longibarbis, the Porthole Catfish
Dianema longibarbis (Porthole Catfish). In all the attention lavished on adorable Cory Cats, which is well deserved, I know I've always neglected their close cousins among the Callichthyinae, the bubblenest-building subfamily. So when I first wrote this in 2002 I had four young Dianema longibarbis, which is smaller (getting to about five inches) and easier to keep than either of the other two Callichthyinae genera, Hoplosternum or Callichthys. They're mouse-colored, with a large dark eye and speckles that arrange themselves into a line of "portholes" down the flanks, strongly countershaded with a white belly. Porthole Cats are like Cories redesigned on racier lines for grace and speed, with a long flattened snout that carries two pairs of barbels, a high sail of a dorsal fin and a deeply forked tail fin.
Breeding these catfish is a rare event, which involves a bubblenest, I hear. (There is an article on breeding Hoplosternum thoracatum by Len Rebeck at The Fish Room.) As they mature, the Dianema females will be larger and broader than the males, but at just under two inches they aren't giving any clues yet. I'm also told that the spiny first ray of the pectoral fins will be thicker in the males. D. longibarbis were first imported into the U.S. in 1955, according to William Innes, Exotic Aquarium Fishes. I don't see them all that often, so I grabbed mine when I had the chance.
These mild-tempered social catfish only thrive in the company of their own kind. The first of them were found in the Rio Ampiyacu, which empties into the upper Amazon at Pevas, Peru, but they are widely distributed in creeks and shorelines of small tributaries of the Amazon, both upstream from Iquitos, whence they are exported, and downstream in the stretch of Amazon between Santarem and Tabatinga, and also in the right-bank tributaries Xingú and Pacayá. The Germans call them "Torpedo Cats." From the forward placement of their mouths, you wouldn't expect them to spend all their time grubbing in the bottom, and they don't. They'll dash to the surface to swallow a mouthful of air like Cories or to eat flakes as happily as they stand on their heads to root out blackworms. Porthole Cats will hold a place in mild current for minutes at a time, or rest motionless, tilted upward, lying on a leaf. An experienced fishkeeper commented to me recently that these are one of the few catfish with forward-facing mouths you can trust with smaller fishes.
If mine had horizontal stripes on their tails, they'd be the "other" Dianema, D. urostriata. I see that Dennis Rawlinson describes a spawning of D. urostriata at www.planetcatfish.com. In his first report (Feb 2000) the spawning took place under a floating plastic lid, at pH 6.2, hardness less than 2oGH, and a cool temperature of 68-72oF. Dennis reduced the water depth to 4 or 5 inches. Alas, the first clutch of eggs got eaten.
A third Dianema, being called "Red Ituxi", for the location of their discovery and the warm russet tones of their coloring, were imported into Germany in 2011 by the rare fish specialist importers Aquarium Glaser of Frankfort.
Links.Dianema longibarbis at FishBase. Porthole catfish at Wikipedia. A species profile is at PlanetCatfish.