Notholebias cruzi

Notholebias cruzi is a small annual killifish belonging to the family Rivulidae, a group renowned for their remarkable adaptation to ephemeral wetland habitats. Native to temporary pools and seasonally flooded grasslands in South America, this species has evolved a life-history strategy in which eggs survive burial in mud through the dry season, hatching rapidly once rains return and the pools refill. Adults display the characteristic vivid coloration typical of annual killifish, with males typically more boldly patterned than females, likely as a result of sexual selection within short-lived, densely populated breeding pools.

Notholebias cruzi is currently classified as Critically Endangered (CR) by the IUCN, with a population trend that is decreasing. Its restricted range and reliance on a very specific type of temporary wetland make it exceptionally vulnerable to habitat modification, drainage, and land conversion for agriculture and urban development, all of which have accelerated in the lowland regions where the species occurs. Because annual killifish cannot disperse between isolated pool systems, even localized habitat destruction can eliminate entire populations with little chance of natural recolonization.

Conservation attention for small-range Rivulidae species has been growing, with regional herpetological and ichthyological societies increasingly prioritizing wetland surveys and ex situ breeding programs among aquarium hobbyist networks, which have historically played a valuable role in maintaining genetic stock of threatened annual killifish. This hobbyist-driven conservation breeding offers a genuine point of optimism, as captive populations can serve as a safeguard against extinction while field conservation and habitat protection efforts continue to develop. Continued monitoring of remaining wetland fragments and increased legal protection for seasonal pool ecosystems will be essential to prevent further decline of this Critically Endangered species.

This critically endangered killifish inhabits temporary pools, shallow wetlands, and seasonal water bodies in the Atlantic Forest region of southeastern Brazil. The species depends on small, ephemeral freshwater habitats that fill during rainy seasons and may dry completely during drought periods.