Threatened fishes of the world: Gambusia eurystoma Miller, 1975 (Poeciliidae)

Abstract

Common names: Widemouth mosquitofish (US), Guayacon del Azufre (MX). Conservation status: Designated ‘critically endangered’ by the IUCN based on highly localized occurrence, small area inhabited, and decline of habitat quality. The species is protected by Mexican law (SEDESOL 1994). Identification: Small-bodied mosquitofish closely related to G. sexradiata. It is characterized by having a compact body with short and rounded fins; a large head with a broad mouth; 30 scales in the lateral line; small black spots irregularly distributed on the ventral part of the body and the unpaired fins; and details in the gonopodium morphology (Miller 1975). Illustration by Madlen Ziege. Distribution: Only known from the Banos del Azufre (Rio Grijalva system), west of Teapa, Tabasco and Chiapas, Mexico. Ecology: Gambusia eurystoma inhabits the outflow of hydrogen sulfide-rich springs, where it is locally abundant. Unlike Poecilia sulphuraria, with which the species co-occurs, G. eurystoma does not occur in the immediate spring areas, but prefers deeper areas with lower H2S concentrations (Tobler et al. 2008). The substrate consists mostly of a layer of anoxic mud. Threats: Gambusia eurystoma is threatened by intense habitat alterations. A hotel complex is situated in the immediate spring area and many of the springheads are used for recreational purposes. Intense cattle grazing altered the riparian vegetation of springs and outflow. Conservation recommendations: The species is protected by Mexican law, but no specific conservation actions have been taken. Steps should be taken to minimize the impact of and pollution by the recreational use of the springheads. A restoration of the riparian buffer is recommended.