Amargosa River pupfish

Amargosa River pupfish
Conservation status
	; Critically Imperiled (NatureServe)
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Cyprinodontiformes
Family:	Cyprinodontidae
Genus:	Cyprinodon
Species:	C. nevadensis
Subspecies:	C. n. amargosae
Trinomial name
	Cyprinodon nevadensis amargosae; R. R. Miller

Last updated November 16, 2024

Description

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).^[1] 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.^[2] 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.^[2] 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.^[3] 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.^[3] Smaller inverterbrates as food seemed to have greater importance in other seasons.^[3]

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.^[5] 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.^[5] 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.

Distribution

The Amargosa River pupfish is found in two distinct areas of perennial flow along the lower Amargosa River in Death Valley, California with a dry stretch of riverbed measuring 16 km between them.^[2] The upstream range is near Tecopa, and the downstream range is near Saratoga Springs. Pupfish inhabit areas of the Tecopa Bore habitat where temperatures can exceed 36°C, although they generally prefer temperatures closer to 30°C.^[8] Water temperatures in the Amargosa River vary seasonally from 10°C to 38°C, with possible near-freezing conditions during extreme winters.^[2] Younger pupfish are more tolerant of higher temperatures than adults and typically inhabit the warmer, shallower waters (around 5 cm deep) near the shore, where they are able to find refuge from predators and reduced competition for food.^[2]

The overall abundance of the Amargosa River pupfish is low due to limited distributions, making conservation efforts critical for their survival. Habitat fragmentation and water diversion for agricultural purposes have significantly impacted the species’ range. The pupfish's preference for shallow, warm waters means that even the slightest alterations to the water flow can reduce suitable habitats threatening the already limited populations. Additionally, invasive species such as non-native fish and aquatic plants further increase these challenges by competing for resources and altering ecosystem dynamics. A survey conducted in 2010 reported that populations of non-native red swamp crayfish (Procambarus clarkii) and western mosquito fish (Gambusia affinis) were captured in much greater numbers compared to native pupfish, especially in areas heavily infested with non-native saltcedar (Tamarix ssp.).^[9] Based on the survey, it was hypothesized that the invasion of saltcedar could result in a decrease in native species.^[9] While saltcedar is a non-native invasive species in the Amargosa River, restoration efforts should prioritize other aquatic invasives such as cattail and common reed because they are disrupting flow velocities and harming pupfish populations.^[9]

Breeding

During the breeding season, males’ brighter colors may become more intense due to hormonal changes, which not only attract potential mates but also communicate territorial dominance. Juveniles are typically more muted in coloration and lack the distinctive markings present in adults. They are generally more transparent than adults as well. This transparency helps juveniles avoid detection by predators, as they are vulnerable during this early stage of life. Recent research has found that male Amargosa River pupfish change their coloration during the breeding season due to a combination, of social, and hormonal factors. Influences such as water temperature and light levels, along with competition for mates, all play an essential role in the males’ shift in coloration. When the water temperature increases and there is a greater abundance of light, the males’ colors become more vibrant, which helps attract a mate and establish dominance over the other males. Thyroid hormones are crucial in this process because they not only support reproduction but also help the fish quickly adapt to changes in their environment.^[10] These hormones regulate their metabolism, which boosts the males’ coloration during breeding, providing them with the extra energy required for their flamboyant displays. Environmental temperature plays an important role in regulating the pupfish breeding.^[10]

The Amargosa River pupfish have a short breeding season that occurs during the warmer months and engage in oviparous reproduction, with females laying eggs in shallow vegetated areas of the river bed. The optimal temperature for the pupfish egg production is approximately 24°C to 32°C.^[10] When the temperature rises above 32°C , the chances of the pupfish producing viable eggs decreases, leading to majority of the eggs lacking yolk or underdeveloped chorions.^[10] At 34°C or higher, reproduction may not occur.^[10] Males exhibit territorial behavior during the breeding season, often displaying more vibrant colors to attract females. Additionally, changes in water quality such as fluctuations in pH and salinity also impact how intensely the males display their colors. The brighter coloration in males is thought to be a form of sexual selection, signaling fitness to potential mates while simultaneously deterring rival males. Amargosa River pupfish largely breed in loose aggregations where males show little aggression and regularly court females.^[12] Some males however, establish and defend reproductive territories in the warm, shallow edges of the river.^[12] These territorial males are aggressive and infrequently court females.^[12] The typical lifespan of the Amargosa River pupfish is quite short, generally around 1 year.^[5] These pupfish reach sexual maturity in a few months at around 30 mm long due to their rapid lifecycle.^[8] The age and growth of this species can be estimated using their otoliths, which are small ear bones that can be analyzed for growth rings similar to tree rings. The Cyprinodon genus is known for its diverse adaptations to extreme environments, which is evident in its physical characteristics and behavior.^[5]

Biology and Morphology

The Amargosa River pupfish demonstrates incredible adaptability to extreme conditions including high temperatures, salinity fluctuations, and low oxygen levels in its habitat. These conditions are characteristic of the harsh environments within the Amargosa River system, especially in the hot desert climate of Death Valley. This pupfish species can withstand water temperatures ranging from near freezing to over 104 F° in summer, temperatures that would be lethal to many other fish species. In addition to the temperature, the Amargosa River pupfish exhibits a remarkable capacity to survive in waters with varying levels of salinity. Salinity is a crucial environmental factor that influences the distribution and survival of aquatic organisms.^[13] This species are known as euryhaline fish, enabling them to withstand changing salt concentrations.^[13] Their adaptability is facilitated by the fish's ability to regulate the osmotic balance within its cells, allowing it to cope with changes in salt concentration that occur due to evaporation or fluctuating river flow. Specialized cells in the gills and kidneys help the pupfish maintain homeostasis by excreting excess salt in highly saline conditions or conserving salts when freshwater levels increase.^[13]

In the slow-moving or stagnant waters of the Amargosa River, oxygen levels can drop significantly, especially during the summer. The Amargosa River pupfish have developed strategies to survive in low-oxygen environments. It can increase its reliance on anaerobic respiration, which does not require oxygen, for a short period of time. This species of fish also displays behavioral adaptations, such as moving to the water surface where oxygen concentration is higher or seeking cooler microhabitats where oxygen solubility is greater.

The body shape, behavior, and even the brain of the pupfish are flexible so that its development is influenced by the environmental conditions early life.^[15] This flexibility is known as phenotype plasticity.^[15] In the case of pupfish, studies of how the environment influences phenotypic development are leading to new insights about how these fish respond to environmental change.^[15] Moreover, recent research has highlighted the role of arginine vasotocin (AVT), a hormone that influences social behavior and osmoregulatory function in Amargosa River pupfish. Variations in AVT expression among different populations throughout Death Valley suggest adaptive changes in aggression and osmoregulation.^[12] Experiments have shown that administering AVT reduces aggressive behavior in the male pupfish, both in laboratory settings and in the wild, indicating that AVT plays an important role in modulating social interactions.^[12] These adaptations make the Amargosa River pupfish an excellent subject for studying evolutionary mechanisms of resilience in extreme environments. Its survival strategies provide insights into how fish can rapidly adapt to harsh conditions, showcasing the effects of natural selection and genetic variability in isolated and stressful habitats. Studying these adaptations can also help researchers understand how other aquatic species might cope with environmental changes brought about by climate change, such as increasing temperatures and altering freshwater availability.^[15]

Conservation Status

The Amargosa River pupfish is listed as critically imperiled by Nature Serve and considered threatened under the California Endangered Species Act. The population decline is attributed to several factors, including groundwater extraction, habitat fragmentation, and invasive species. The introduction of non-native fish, such as mosquitofish, poses significant threats due to predation and competition for resources. Recent studies have shown that rising water temperatures due to climate change, not only diminish suitable habitats, but can also result in smaller fish sizes and altered body morphology.^[16] These morphological changes could further impact the species’ survival by impacting their reproductive success and ability to compete for resources. For example, a significant decline in body mass has been observed, with males and females showing a 33.4% and 39.0% reduction, following temperature increases from climate change.^[16] Additionally, morphological changes have been discovered, such as partial or complete loss of paired pelvic fins in about 34% of the population.^[16] This fin loss can impair social behaviors like territorial defense, impacting reproductive success. Climate change is also worsening these threats, as increased temperatures and reduced water availability may further harm the already fragile habitats of the pupfish.

Conservation efforts focus on habitat restoration, groundwater management, and monitoring population trends to reduce the risks facing the species. Addressing temperature increases is crucial, as warmer waters accelerate metabolic rates, leading to reduced growth rates, and limiting the potential and resilience of the species.^[16] Understanding the physiological responses of fish to increased temperatures, and how these responses differ across populations is essential for predicting changes in fish communities as their habitats become warmer.^[8] It also helps whether the ability to adapt to varying temperatures could support species survival.^[8] Legal protections under federal and state laws aim to preserve critical habitats, while captive breeding programs have been proposed as a backup strategy to prevent extinction. Furthermore, researchers emphasize the need for adaptive management strategies that account for continuous temperature changes, incorporating prediction of future climate scenarios into conservation planning to ensure the survival of the Amargosa River pupfish.^[16] This species holds ecological significance as an indicator species for the health of the Amargosa River ecosystem.

Related Research Articles

The Death Valley pupfish, also known as Salt Creek pupfish, is a small species of fish in the family Cyprinodontidae found only in Death Valley National Park, California, United States. There are two recognized subspecies: C. s. salinus and C. s. milleri. The Death Valley pupfish is endemic to two small, isolated locations and currently classified as endangered.

The Amargosa River is an intermittent waterway, 185 miles (298 km) long, in southern Nevada and eastern California in the United States. The Amargosa River is one out of two rivers located in the California portion of the Mojave Desert with perennial flow. It drains a high desert region, the Amargosa Valley in the Amargosa Desert northwest of Las Vegas, into the Mojave Desert, and finally into Death Valley where it disappears into the ground aquifer. Except for a small portion of its route in the Amargosa Canyon in California and a small portion at Beatty, Nevada, the river flows above ground only after a rare rainstorm washes the region. A 26-mile (42 km) stretch of the river between Shoshone and Dumont Dunes is protected as a National Wild and Scenic River. At the south end of Tecopa Valley the Amargosa River Natural Area protects the habitat.

<span class="mw-page-title-main">Tecopa pupfish</span> Extinct subspecies of fish

The Tecopa pupfish is an extinct subspecies of the Amargosa pupfish. The small, heat-tolerant pupfish was endemic to the outflows of a pair of hot springs in the Mojave Desert of Inyo County, California. Habitat modifications, the introduction of non-native species and hybridization with the related Amargosa River pupfish led to its extinction around 1979.

The Shoshone pupfish is a subspecies of Amargosa pupfish from California in the United States. They are spring-dwelling fish, endemic to Shoshone Springs on the outskirts of Shoshone, Inyo County, California. In 1969, the Shoshone pupfish was declared extinct until their eventual rediscovery by a team of biologists during a survey of Shoshone Springs in 1986. Currently, they are listed as endangered by the American Fisheries Society and are a species of special concern according to the California Department of Fish and Wildlife. Several stocks of the fish are being cultivated in captivity at the University of Nevada, Las Vegas and University of California, Davis for reintroduction into the Shoshone Spring. Today, people pass through the town of Shoshone to visit the spring site and view the rare pupfish, where some infographics and signs educate visitors about them.

The Devils Hole pupfish is a critically endangered species of the family Cyprinodontidae (pupfishes) found only in Devils Hole, a water-filled cavern in the US state of Nevada. It was first described as a species in 1930 and is most closely related to C. nevadensis and the Death Valley pupfish. The age of the species is unknown, with differing analyses offering ranges between one thousand and sixty thousand years. It is a small fish, with maximum lengths of up to 30 mm (1.2 in). Individuals vary in coloration based on age and sex: males are bright metallic blue while females and juveniles are more yellow. A defining trait of this species is its lack of pelvic fins. The pupfish consumes nearly every available food resource at Devils Hole, including beetles, snails, algae, and freshwater crustaceans, with diet varying throughout the year. It is preyed on by the predaceous diving beetle species Neoclypeodytes cinctellus, which was first observed in Devils Hole in 1999 or 2000. Reproduction occurs year-round, with spikes in the spring and fall. Females produce few eggs and the survivorship from egg to adult is low. Individuals live 10–14 months.

Pupfish are a group of small killifish belonging to ten genera of the family Cyprinodontidae of ray-finned fish. Pupfish are especially noted for being found in extreme and isolated situations. They are primarily found in North America, South America, and the Caribbean region. As of August 2006, 120 nominal species and 9 subspecies were known. Several pupfish species are extinct and most extant species are listed. In the U.S., the most well-known pupfish species may be the Devils Hole pupfish, native to Devils Hole on the Nevada side of Death Valley National Park. Since 1995 the Devils Hole pupfish has been in a nearly steady decline, where it was close to extinction at 35–68 fish in 2013.

Devils Hole is a geologic formation located in a detached unit of Death Valley National Park and surrounded by the Ash Meadows National Wildlife Refuge, in Nye County, Nevada, in the Southwestern United States.

Cyprinodon is a genus of pupfishes found in waters that range from fresh to hypersaline. The genus is primarily found in Mexico, the Caribbean Islands and southern United States, but C. variegatus occurs as far north as Massachusetts and along the entire Gulf of Mexico coastline, and C. dearborni and C. variegatus are found in northern South America. Many species have tiny ranges and are highly threatened, in some cases already extinct. Cyprinodon are small; the largest reaches 10 cm (3.9 in) in length and most other species only reach about half that size.

The sheepshead minnow, also known as sheepshead pupfish, is a species of ray-finned fish in the family Cyprinodontidae, the pupfishes. It is found in salt marsh and estuary environments and is native to the eastern coasts of North and Central America.

Robert Rush Miller was an important figure in American ichthyology and conservation from 1940 to the 1990s.

The Comanche Springs pupfish is a species of pupfish in the family Cyprinodontidae. It is endemic to Texas, and is now found only in spring-fed pools near Balmorhea, a small town in West Texas.

The Owens pupfish is a rare species of fish in the family Cyprinodontidae, the pupfish. It is endemic to California in the United States, where it is limited to the Owens Valley. It is a federally listed endangered species of the United States. This pupfish is up to 5 centimetres long, the largest males sometimes longer. The male is blue-gray, turning bright blue during spawning. The female is greenish brown with a silvery or whitish belly.

The Catarina pupfish was a diminutive species of fish in the family Cyprinodontidae, first described in 1972. It was endemic to a spring in Nuevo León, Mexico. In an attempt of saving the rapidly declining species, some were brought into captivity in the late 1980s and early 1990s, but it proved very difficult to maintain. In 1994 it became extinct in the wild. Gradually the captive populations also perished. The last male died in 2014 and the species became extinct.

The desert pupfish is a rare species of bony fish in the family Cyprinodontidae. It is a small fish, typically less than 7.62 cm (3 in) in length. Males are generally larger than females, and have bright-blue coloration, while females and juveniles are silvery or tan. A notable attribute of the desert pupfish is their ability to survive in environments of extreme salinity, pH, and temperature, and low oxygen content. The desert pupfish mates in a characteristic fashion, wherein compatible males and females will come in contact and collectively jerk in an s-shape. Each jerk typically produces a single egg that is fertilized by the male and deposited in his territory. Breeding behavior includes aggressive arena-breeding and more docile consort-pair breeding.

The Sonoyta pupfish or Quitobaquito pupfish is an endangered species of pupfish from Sonora in Mexico and Arizona in the United States.

The Death Valley freshwater ecoregion is a freshwater ecoregion in the western United States. It consists of endorheic rivers, lakes, and springs in the drainages of the Owens, Amargosa, and Mojave Rivers, in central-eastern California and southwestern Nevada.

The Saratoga Springs pupfish is a subspecies of the Amargosa pupfish of the family Cyprinodontidae. The native population is endemic to Saratoga Springs, a small wetland in Death Valley National Park in the United States.

Cyprinodon nevadensis is a species of pupfish in the genus Cyprinodon. The species is also known as the Amargosa pupfish, but that name may also refer to one subspecies, Cyprinodon nevadensis amargosae. All six subspecies are or were endemic to very isolated locations in the Mojave Desert of California and Nevada.

Cyprinodon desquamator is a scale-eating species of pupfish in the genus Cyprinodon. It is endemic to hypersaline interior lakes on San Salvador Island, Bahamas. It coexists alongside two other closely related Cyprinodon species C. brontotheroides and C. variegatus. Together, these three species represent a recent adaptive radiation, each having moved into a difference niche within their specialized environment. Each of these species are defined by distinct trophic adaptations that have affected various aspects of their functional morphology, behavior, strike kinematics, and reproductive coloration.

Poecilia vandepolli, or Van de Poll's molly, is a poeciliid fish native to the ABC islands of the Lesser Antilles, namely Aruba, Bonaire, and Curaçao. It is a euryhaline species and one of the most common fish in its range, inhabiting fresh, brackish, salt, and hypersaline waters. The fish vary significantly in size and color depending mostly on the salinity of their environment. The saltwater specimens grow faster and become more robust and more colorful, but the species is drawn to the freshwater habitats which disappear in each dry season and must be recolonized when the rains return.

References

1 2 NatureServe (7 April 2023). "Cyprinodon nevadensis amargosae". NatureServe Network Biodiversity Location Data accessed through NatureServe Explorer. Arlington, Virginia: NatureServe. Retrieved 18 April 2023.
1 2 3 4 5 "Amargosa River Pupfish - Cyprinodon nevadensis amargosae (Miller)".^{[ full citation needed ]}
1 2 3 Naiman, Robert J. (1979). "Preliminary Food Studies of Cyprinodon macularius and Cyprinodon nevadensis (Cyprinodontidae)". The Southwestern Naturalist. 24 (3): 538–541. doi:10.2307/3671312. JSTOR 3671312.
↑ Lema, Sean (2008) Male and female Amargosa river pupfish (Cyprinodon nevadensis) [Photograph] https://www.americanscientist.org/article/the-phenotypic-plasticity-of-death-valleys-pupfish
1 2 3 4 "Amargosa River Pupfish". California fish species. University of California, D. of A. and N. R.
↑ California Department of Fish and Wildlife, Male pupfish in an aquarium [Photograph] https://wildlife.ca.gov/Regions/6/Desert-Fishes/Desert-Pupfish
↑ California Fish and Game (2016) Distribution of Amargosa River pupfish [Map] file:///Users/admin/Downloads/Distribution%20of%20Amargosa%20River%20pupfish%20(Cyprinodon%20nevadensis%20amargosae)%20in%20Death%20Valley%20Nationa.pdf
1 2 3 4 Lema, Sean C.; Chow, Michelle I.; Resner, Emily J.; Westman, Alex A.; May, Darran; Dittman, Andrew H.; Hardy, Kristin M. (2016). "Endocrine and metabolic impacts of warming aquatic habitats: differential responses between recently isolated populations of a eurythermal desert pupfish". Conservation Physiology. 4 (1): cow047. doi:10.1093/conphys/cow047. PMC 5100229 . PMID 27833749.
1 2 3 Hereford, Mark E. (2016). Relative distribution and abundance of fishes and crayfish in 2010 and 2014 prior to saltcedar (Tamarix ssp.) removal in the Amargosa River Canyon, southeastern California (Report). doi: 10.3133/ofr20161112 .
1 2 3 4 5 Lema, Sean C.; Chow, Michelle I.; Dittman, Andrew H.; May, Darran; Housh, Madeline J. (October 2022). "Accustomed to the heat: Temperature and thyroid hormone influences on oogenesis and gonadal steroidogenesis pathways vary among populations of Amargosa pupfish (Cyprinodon nevadensis amargosae)". Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology. 272: 111280. doi: 10.1016/j.cbpa.2022.111280 .
↑ Sullivan, Joseph (2006) Vibrant coloration display during breeding season [Photograph] https://calfish.ucdavis.edu/species/?uid=2&ds=698#:~:text=Spawning%20by%20Amargosa%20Pupfish%20varies,a%20female%20among%20the%20crowd.
1 2 3 4 5 Lema, Sean C.; Nevitt, Gabrielle A. (December 2004). "Exogenous vasotocin alters aggression during agonistic exchanges in male Amargosa River pupfish (Cyprinodon nevadensis amargosae)". Hormones and Behavior. 46 (5): 628–637. doi:10.1016/j.yhbeh.2004.07.003.
1 2 3 Kültz, Dietmar (1 June 2015). "Physiological mechanisms used by fish to cope with salinity stress". Journal of Experimental Biology. 218 (12): 1907–1914. doi:10.1242/jeb.118695.
↑ Freese, S (2006) Aggressive initiation and response of Amargosa River pupfish with AVT [Graph] https://www.americanscientist.org/article/the-phenotypic-plasticity-of-death-valleys-pupfish
1 2 3 4 Lema, Sean C. (2008). "The Phenotypic Plasticity of Death Valley's Pupfish". American Scientist. 96 (1): 28. doi:10.1511/2008.69.28.
1 2 3 4 5 Lema, Sean C.; Bock, Samantha L.; Malley, Morgan M.; Elkins, Emma A. (October 2019). "Warming waters beget smaller fish: evidence for reduced size and altered morphology in a desert fish following anthropogenic temperature change". Biology Letters. 15 (10): 20190518. doi:10.1098/rsbl.2019.0518. PMC 6832196 . PMID 31615375.