The new species is named Rivulus giarettai, after the herpetologist Ary Giaretta, who was the first to collect the new species, by Wilson Costa in a recent issue of the journal Ichthyological Exploration of Freshwaters.
Rivulus giarettai is a member of the subgenus Melanorivulus, and is distinguished from all other members of that subgenus in having the males with red pigmentation of the flank arranged in irregular lines to form a vermiculate pattern. It is further distinguished by the following combination of characters: 34"36 scales on the longitudinal series, 30"32 caudal-fin rays, 3"4 vomerine teeth, vestigial ventral process of the anguloarticular, curved first epibranchial, males with intense greenish blue of greenish golden to purplish blue coloration above the anal-fin base, imperceptible black pigmentation on the head and humeral region of the males, and caudal fin with bars in both sexes.
The new species is only known from three localities in the middle Araguari River drainage, which is part of the upper Paran River drainage, where it inhabits streams flowing through Cerrado (a savanna-like vegetation). The fish were found at the surface close to vegetation with the water being clear to slightly turbid and having a pH of 5.2"5.9.
For more information, see the paper: Costa, WJEM (2008) Rivulus giarettai, a new killifish from the Araguari River drainage, upper Paran River basin, Brazil (Cyprinodontiformes: Rivulidae). Ichthyological Exploration of Freshwaters 19, pp. 91"95.