A new South American killifish in the genus Rivulus has been described.
The description of Rivulus illuminatus is published by Wilson Costa in the latest issue of the journal Ichthyological Exploration of Freshwaters.
The new species is known only from the type locality, the floodplains of crrego da Queixada in the upper Paran River drainage in central Brazil.
Rivulus illuminatus is a member of the subgenus Melanorivulus, which was recently erected to include Rivulus species endemic to central and northeastern South America.
It can be distinguished from all other members of the subgenus in having 6 pelvic-fin rays.
Rivulus illuminatus further differs from congeners in having a combination of the following: F-patterned frontal squamation. males with longitudinal rows of red dots on the flanks and reduction of black pigmentation on the head, females with a white to light yellow horizontal mark above the caudal spot, 32"33 caudal-fin rays, 33"35 scales in longitudinal series, 8 scales in transverse series, dorsal-fin origin at vertical through base of 7th or 8th anal-fin ray, and tip of pelvic fin reaching between base of 1st and 3rd anal-fin rays in males.
The new species is named forthe bright blue colour of the falnks in males (illuminatus = Latin for illuminated).
At the type locality, the fish were found in interconnected pools about 30 cm deep in a shallow swamp; the pH of the water was 5.9.
For more information, see the paper: Costa, WJEM (2007) Rivulus illuminatus, a new killifish from the serra dos Caiaps, upper rio Paran basin, Brazil (Teleostei: Cyprinodontiformes: Rivulidae). Ichthyological Exploration of Freshwaters 18, pp. 193"198.