April 03, 2013
The fish, dubbed Cyanogaster noctivaga or the blue-bellied night wanderer, is described in the journal Ichthyological Exploration of Freshwaters. The species may have gone undiscovered in one of the Amazon's most studied tributaries — the Rio Negro — because it is nocturnal, tiny and transparent. With a maximum length of 17 mm, it is one of the smallest known vertebrates, measuring only 7 mm more than the world's tiniest fish.
"It is a strange little animal, completely transparent with an otherwise unique color pattern," said study co-author Ralf Britz, an ichthyologist at London's Natural History Museum.
Another reason the night-active Cyanogaster noctivaga may have been undetected is its habitat: the highly acidic blackwater of the Rio Negro. The river is so dark due to dissolved tannins that it is often likened to a cup of well-brewed black tea.
TOP: Dead Cyanogaster noctivaga specimen — the fish was difficult to capture alive due to its small size, according to the authors. BOTTOM: Live blue-bellied night wanderer. Photo courtesy of George Mattox et al (2013).
Interestingly, the world's smallest freshwater fish, Paedocypris progenetica lives in similar conditions in southeast Asia.
"The Rio Negro in Brazil, like the Asian peat swamp forests, has acidic blackwaters and like the peat swamps, it harbors a large number of miniature species," Britz explained in a press release. "Small size seems to be favored in mineral-poor water and Cyanogaster is another example of this rule."
The authors placed the species in its own genus after they determined the fish has a unique arrangement of teeth relative to others in the tetra family.
"All other members of the subfamily Stevardiinae and actually most members of the family Characidae have a different number and arrangement of teeth," Britz said. So this helps to demonstrate that our little ‘bluebelly’ is something quite different, a new genus."
CITATION: Mattox, G.M.T., Britz, R., Toledo-Piza, M. & Marinho, M.M.F (2013). Cyanogaster noctivaga, a remarkable new genus and species of miniature fish from the Rio Negro, Amazon basin (Ostariophysi: Characidae). Ichthyological Exploration of Freshwaters, vol. 23, no. 4, pp. 297-318