A new cave species of Rhamdia (Siluriformes: Heptapteridae) from Serra do Ramalho, northeastern Brazil, with notes on ecology and behavior

Abstract

Rhamdia enfurnada, a new troglobitic (exclusively subterranean) catfish, is described from the Gruna do Enfurnado, Serra do Ramalho, southwestern Bahia State, middle São Francisco River basin. It differs from epigean congeners from the São Francisco River basin by the variable eye size, ranging from reduced to externally invisible (bilateral asymmetry in development of eyes is frequently observed), with a conspicuous orbital concavity (orbital diameter varying from 6.4 to 13.6% of head length in R. enfurnada and from 14.5 to 24.4% in the epigean species); by the dark pigmentation reduced due to a decrease in density of melanophores, and also variable. In comparison to other cave species, R. enfurnada presents a low degree of troglomorphism regarding development of eyes and pigmentation, indicating a relatively short time evolving in isolation in the subterranean environment: R. reddelli is described as lacking eyes and with almost no pigmentation; likewise, R. macuspanensis and R. laluchensis as having rudimentary eyes, covered with skin and not visible externally, and with reduced body pigmentation; R. zongolicensis is also almost devoid of dark pigmentation, but eyes are less reduced than in R. reddelli. R. quelen urichi, also does not present any trace of eyes externally, but the body coloration is described as pale yellowish brown. Rhamdia guasarensis has a concave dorsal profile of head and a complete absence of pigmentation and eyes. The population density (preliminarily estimated in 0.1-0.2 individuals m-2 in average, and reaching 10 individuals m-2, in the dry season and size (several thousands of individuals) of R. enfurnada may be considered high for cave fish standards. Rhamdia enfurnada exhibited an increased midwater activity when compared to their typically bottom-dwelling epigean relatives; are mostly indifferent to light and moderately aggressive.