New data on cistern catfish, Phreatobius cisternarum, from subterranean waters at the mouth of the Amazon River (Siluriformes, Incertae Sedis)

Abstract

Data on new specimens of the rare subterranean catfish Phreatobius cisternarum are reported. Specimens were collected from hand-dug wells in the region of the mouth of the Amazon river, Brazil. A revised diagnosis of Phreatobius is proposed, and P. cisternarum is redescribed on the basis of new and previously available material. Included are data on coloration, both in life and preserved, SEM observations of external morphology, morphometric and meristic data. One juvenile specimen, the first known of the species, is reported and illustrated. The new and previously available material reveal considerable intraspecific variation in several morphological traits of P. cisternarum. Despite its rarity in collections, P. cisternarum seems to be common in wells in the vicinity of the city of Belém and on Marajó Island, where many locals know of them. They occur in the superficial phreatic layer, and turn up in hand-dug wells usually from 4 to 13 meters deep. Individual fish hide in orifices of canga rocks at the bottom of wells. Some specimens were maintained in captivity for one-and-a-half year, during which some behavioral observations were recorded. In aquarium conditions, P. cisternarum is an oportunistic predator that feeds vigorously on earthworms and other live invertebrates.