Although usually thought of as “one of those ugly brown fish,” R. cylindraceus was for some time confused with the hermaphroditic R. marmoratus. However, it was eventually determined to be a species in its own right
Hailing from Cuba, this fairly plain fish frequents the freshwater streams that feed into bays and rivers. Although they can tolerate salt in the aquarium, in their native habitat they avoid brackish water for the fresher streams, leaving the saltier habitats to R. marmoratus.
Although usually sporting a colorful pattern of … brown … R. cylindraceus has surprised some researchers, according to Bruce Turner, who maintained some as comparative species to R. marmoratus, with which he was working in the lab. “I discovered … quite by accident, that when raised ab ovo (from the egg) on a diet primarily of brine shrimp, [you could just] watch the reds and oranges come out. The color is quite strong and rather impressive.” A technician had raised some R. cylindraceus fry on the diet used for the R. marmoratus; the males of the next generation were impressive.
Bruce reports that he kept two pair in a two liter beaker on a lab bench (with a floating mop) in full room light for several months, and they attracted a lot of attention from visitors.
Two other strains of this species have been seen in the hobby in recent years, a dark green strain supposedly from Isle of Pines, and a “black” strain referred to as “Al Castro.”
— GCKA Newsletter, February 1998 and March 2002