Simpsonichthys is a genus of annual killifish in the family Rivulidae, endemic to Brazil, where its species live in temporary rain-fed pools and puddles across the Cerrado and other seasonally dry stretches of eastern and central Brazil. They follow the classic annual killifish life history: adults grow, color up, and spawn quickly during the rainy season, then die as their pools dry out, while fertilized eggs lie dormant buried in the damp substrate through the dry months and hatch once rains refill the pool. The atlas's 13 species include the Boiton's pearlfish, and range from about 1 in to 2.5 in.
Killifish keepers prize Simpsonichthys for the often brilliant, multicolored patterning of mature males and for the particular satisfaction of breeding them through the classic peat-moss egg-storage method that mimics their natural dry-season diapause. Conservation is a serious concern for the genus: 6 Vulnerable, 3 Endangered, and 2 Critically Endangered species out of 13, a reflection of how many populations are confined to single small seasonal pools that are easily lost to agricultural conversion and drainage of Cerrado habitat. One species in the atlas is tracked under the CARES conservation priority list.