Amargosa River pupfish

The Amargosa River pupfish (Cyprinodon nevadensis amargosae) is a member of a pupfish species complex which inhabits the watershed of ancient Lake Manly (present day Death Valley in California, USA). Currently, the species inhabits two disjunct perennial reaches of the lower Amargosa River. The upstream portion is near Tecopa and passes through the Amargosa Canyon. The lower portion is northwest of Saratoga Springs, just at the head (southern inlet) of Death Valley, where the Amargosa River turns north to enter the valley. This species is typically found in warm, shallow waters with submerged vegetation.

These diminutive fish subsist on cyanobacteria and algae which are abundant in their habitat. However, they have been known to feed on smaller invertebrates, including mosquito larvae and copepods. This feeding strategy allows them to thrive in environments where other food sources may be scarce. In a study conducted over several seasons, detritus made up the majority of this species' stomach (65% in October, 90% in November) while algae, vascular plants, and animals were minimal. The pupfish's selection of food seems to be dictated by biological and physiochemical restructions placed on the food supply based on their extreme environment. Smaller invertebrates as food seemed to have greater importance in other seasons.

They have a life history adapted to the vagaries of the intermittent nature of their environment. They have a very short generation time (<1 year and usually just a few months), which allows for rapid exploitation of flooded portions of the streambed in years of high flow.

The Amargosa River pupfish is a small fish, typically measuring no more than 2 inches (50 mm) in length as an adult. It has a compressed body with a small terminal mouth. with a complete row of tricuspid teeth and rounded fins aiding in maneuverability within their habitat. Their streamlined body shape reduces drag, allowing the fish to conserve energy as it moves through the water, an essential adaptation in an environment where resources can be scarce. The coloration is typically bluish or greenish with a lighter underside, often exhibiting dark spots and markings on the body and fins. These markings help the pupfish blend with the rocky and sandy riverbeds, providing camouflage from predators. Males often show more vivid colors, especially during breeding seasons, compared to females' muted colors. The breeding season occurs during the summer months when the water temperature is higher and food is most abundant.

The Amargosa River pupfish may be confused with other species in the Cyprinodon genus, such as the Desert pupfish (Cyprinodon macularius) and the Pahrump Valley pupfish (Cyprinodon nevadensis). These species share similar habitats and physical characteristics but can be distinguished by differences in coloration and size as the Amargosa River pupfish tends to have a more elongated body compared to some of its relatives.