Gambusia zarskei Meyer, Schories & Schartl 2010

Gambusia zarskei is a small sized species of the subgenus Arthrophallus (SL in males usually not exceeding 25 mm and in females 35 mm), which is distinguished from all other species of the senilis species group by the following characters: shafts of distal spines of gonopodium ray 3 much prolonged, lateral projection on elbow weekly developed, vs. well developed in G. amistadensis and G. hurtadoi or absent in G. alvarezi, G. gaigei and G. senilis. G. zarskei is also distinguished by the following unique combination of characters: relative gonopodial ray 4p serra length of gonopodium long; frequency distribution of SEL/SEW radius 1.35 – 1.65, vs. 0.95 – 1.25 in G. alvarezi, 1.55 – 1.90 in G. amistadensis, 1.00 – 1.35 in G. gaigei and 0.75 – 1.05 in G. hurtadoi; elbow on gonopodium ray 4a simple and not rounded or distally hooked, vs. usually hooked in G. alvarezi, G. gaigei, G. senilis; 8 dorsal fi n rays, vs. usually 9 in G. alvarezi and G. hurtadoi; black anal spot present vs. absent in G. senilis.

Vertebrae: 30 - 31

Gambusia zarskei inhabits the waters of small warm springs and their outlets at the foot of Sierra San Diego on the northwestern mountain side. The collection sites are small outlets, approx. 0.5 to 2.0 m wide and 0.60 to 1.00 m deep, that flow into the Rio Chuviscar drainage, a tributary of the Rio Conchos, 2 km east of San Diego de Alcalá on an unpaved road. At the type locality (N 28° 35’ 36.2”, W 105° 33’ 00.0”) on March, 18th, 2006 before noon the water had a temperature of 24 to 26 °C, a conductivity of 1486mS, pH 7.85, and a total hardness of 9. The water was crystal clear, fast fl owing and without aquatic vegetation. The substratum consisted mainly of gravel and sand. The brook fl ows in an open area. Accompanying fishes were Gambusia senilis and Cyprinodon spec. Gambusia zarskei was mainly found in water depth of 0.05 to 0.10 m along the water edges, where the water temperature might rises to 34 °C near the hot spring (Ref. 84135).