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 Fran-cisco 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. Rhamdia enfurnada, uma nova espécie de bagre troglóbio (exclusivamente subterrâneo), encontrada na Gruna do Enfurnado, Serra do Ramalho, sudoeste Baiano, Bacia do Médio Rio São Francisco, é aqui descrita. Esses bagres diferem dos congêneres com ocorrência em rios epígeos da bacia do São Francisco pela alta variabilidade no grau de desenvolvimento dos olhos, de apenas ligeiramente reduzidos até externamente invisíveis, com freqüente assimetria bilateral (diâmetro da órbita: comprimento da cabeça variando de 6,4 a 13,6% em R. enfurnada e de 14,5 a 24,4% nos espécimes epígeos examinados); pela pigmentação melânica reduzida devido à diminuição na densidade de melanóforos, também com variação populacional. Comparando-se com outras espécies cavernícolas, R. enfurnada apresenta um baixo grau de troglomorfismo, em relação aos olhos e pigmentação, indicando um tempo de isolamento no ambiente subterrâneo relativamento pequeno: R. reddelli não possui olhos e pouca pigmentação no corpo; da mesma maneira, R. macuspanensis e R. laluchensis apresentam olhos rudimentares, cobertos por pele e não visíveis externamente, além de pigmentação reduzida no corpo; R. zongoli...

VIEWPOINT. Is the Australian subterranean fauna uniquely diverse?

“…The Spelaeogriphacea are only known from two other locations in the world (Brazil and Australia), indicating a shared Gondwanan distribution (Jaume 2008). In South America, the best characterised caves are in central Brazil and include the Serra do Ramalho karst area in Bahia state, well known for its populations of the troglomorphic catfish Rhamdia enfurnada Bichuette & Trajano, 2005(e.g. Mattox et al 2008, and Minas Gerais state, which is well known for its troglobitic invertebrate fauna (Ferriera and Horta 2001;Souza and Ferreira 2010).…”

The blind catfish from the caves of Chapada Diamantina, Bahia, Brazil (Siluriformes: Heptapteridae): description, anatomy, phylogenetic relationships, natural history, and biogeography

“…New heptapterid genus from Chapada Diamantina. -Bichuette & Trajano, 2005: 592. New heptapterids from Bahia [in partim].…”

“…Among heptapterids, this state has been illustrated for Pimelodella sp. (Bockmann & Miquelarena, 2008), Rhamdella cainguae (Bockmann & Miquelarena, 2008), Rhamdia enfurnada (Bichuette & Trajano, 2005), R. muelleri (Silfvergrip, 1996), and R. guasarensis (DoNascimiento et al, 2004). On the other hand, this segment of the supraorbital laterosensory canal is missing in the majority of the members of the "Clade D" of Bockmann & Miquelarena (2008), which includes the Nemuroglanis sub-clade plus Brachyglanis, Gladioglanis, Leptorhamdia, and Myoglanis (and probably Phreatobius).…”

“…obs.). A short and interrupted lateral line is not a common trait among troglobitic heptapterids, such as exemplified by Pimelodella spelaea , Rhamdia enfurnada (Bichuette & Trajano, 2005), R. guasarensis (DoNascimiento et al, 2004), and R. laluchensis (Weber et al, 2003), which have long and complete lateral lines. The lateral line of cave-dwelling ictalurids Satan and Trogloglanis is also short, not exceeding the end of adipose fin (Langecker & Longley, 1993).…”

“…Most species of fishes restricted to subterranean habitats are siluriforms, with about 50 species in the Americas, mainly concentrated in the Neotropical region (Trajano, 2003;Bichuette & Trajano, 2005, 2008Fernandez et al, 2007;Shibatta et al, 2007). The prevalence of siluriforms in the troglobitic habitats, including caves, is likely explained by their morphological/ biological "preadaptations", viz.…”