Filling gaps in the biology of the critically endangered killifish Leptopanchax itanhaensis (Aplocheiloidei: Rivulidae)

Abstract Leptopanchax itanhaensis is a critically endangered annual killifish endemic to temporary aquatic habitats of the Atlantic Forest in southeastern Brazil, yet its biology and ecology remain poorly known. Here, we provide preliminary natural history data based on a 14-month monitoring effort in the Preto River sub-basin, the only region where the species is currently known to occur. We monitored one temporary pool and two roadside ditches, recording a total of 32 individuals, with most captures occurring during the rainy season. The species was repeatedly detected in both natural and artificial temporary habitats, which differed in their physicochemical conditions. Critical thermal maximum values ranged from 33.3 to 37.7 °C, and the thermal safety margin was estimated at 7.41 °C. Diet analysis indicated frequent consumption of Chironomidae larvae and Ostracoda, although most food items were classified as occasional. Eight mature females were analyzed for reproductive traits, revealing low batch fecundity and a bimodal distribution of oocyte diameters, consistent with batch spawning. Female body size was positively associated with oocyte diameter, but not with fecundity. Together, these findings provide the first integrated natural history account for L. itanhaensis and help fill key knowledge gaps for the conservation of this highly threatened species.