Diving in the sand: the natural history of Pygidianops amphioxus (Siluriformes: Trichomycteridae), a miniature catfish of Central Amazonian streams in Brazil

The natural history of Pygidianops amphioxus de Pinna and Kirovskyi (Neotropical Ichthyology 9:493–504, 2011), a highly specialized sand-dwelling catfish species, was studied based on underwater observations in a small forest stream in the central Amazon. Information on the feeding and reproductive biology was obtained by means of analyses of preserved specimens. These miniature catfishes remained buried in the sand at the bottom of the stream and were never observed swimming in open water. The catfish consumed small benthic invertebrates, particularly Chironomidae larvae and Harpacticoida copepods, which were most likely captured by suction feeding inside the sand banks. Pygidianops amphioxus displays sexual dimorphism in the shape of the urogenital papilla and in the body length, with adult females being relatively longer than males. Sexually mature females were found throughout the year and carried a small number of proportionally very large oocytes. A short duration (24 h) experiment conducted in aquaria revealed that these small catfishes exhibit the predominantly nocturnal habits typical of most Siluriformes.