Brazilian killifish expert Wilson Costa has named a new species of aplocheiloid killifish from central Brazil in a recent issue of the journal Ichthyological Exploration of Freshwaters.
The new species, named Rivulus formosensis is a member of the subgenus Melanorivulus, and is distinguished from other members of the subgenus in having the males with red marks on flanks arranged in a chevron-like pattern with branching on the upper portion forming Y-shaped marks. It is additionally distinguished by a combination of: males with intense greenish blue to purplish blue above anal-fin base and without a sub-basal red stripe on the dorsal fin, females without black reticulation on the head and lacking orange pigmentation on the caudal fin, 29"31 scales in the longitudinal series, E-patterned frontal squamation, 31"33 caudal-fin rays, predorsal length in males 75.1"79.5% standard length and length of the anal-fin base 20.6"23.0% standard length in males and 18.2"20.0% standard length in females.
Rivulus formosensis is known from the Formoso river floodplains of the upper Corrente River drainage (part of the upper Paran River drainage) in central Brazil, at an altitude of 745"800 m above sea level.
The fish were found in open areas that were highly exposed to sunlight and the water was light yellow with pH 5.6. The species is named after the Formoso river floodplains, where this species is found.
For more information, see the paper: Costa, WJEM (2008) Rivulus formosensis, a new aplocheiloid killifish from the upper Corrente River drainage, upper Paran River basin, central Brazil (Cyprinodontiformes: Rivulidae). Ichthyological Exploration of Freshwaters 19, pp. 85"90.