Types of pupfish

The sheepshead minnow (Cyprinodon variegatus), 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.

Description

The sheepshead minnow is a deep-bodied fish; its body, exclusive of its tail, is nearly half as deep as it is long. The length of the fish averages 30 mm (1.2 in); it ranges to a maximum of 75 mm (3 in). It is laterally compressed with flat sides, an arched back and a small head with a flattened top. The small mouth is at the end of the snout and the teeth are large and wedge-shaped with three cusps. The pectoral fins are large and extend past the origins of the small pelvic fins. The origin of the anal fin hardly overlaps the trailing edge of the dorsal fin. The caudal peduncle is thick and the caudal fin is truncated and square-ended. The arrangement of the fins, the deep body and the tri-cuspid teeth help to distinguish this fish from the mummichog (Fundulus heteroclitus), which is found in the same habitats. The body is covered by large, circular scales, the ones on the cheeks and the top of the head and a single scale just above the pectoral fin being the largest. The male is generally larger and more deep-bodied than the female, with larger dorsal, pelvic and anal fins.

The color of the sheepshead minnow is olive green above and yellowish below. Juveniles have irregular transverse dark bars and the females keep these as they mature, while the males lose theirs. The dorsal fin is dark while the pectoral, pelvic and anal fins are orange. During the breeding season the male becomes very colorful with steel blue upper parts in front of the dorsal fin, lustrous green upper parts behind and deep salmon-pink underparts.

Distribution and habitat

The sheepshead minnow is native to the eastern coast of the United States. Its range extends from Cape Cod southwards to the Yucatan peninsula in Mexico, also the West Indies. It is found in brackish water in bays, inlets, lagoons, saltmarshes and similar locations with little wave action and sandy or muddy bottoms. It is tolerant of wide variations in salinity and is also found in hypersaline conditions.

Behavior

The sheepshead minnow is an omnivore, eating both animal and vegetable matter. Its diet mainly consists of detritus, microalgae, crustacean larvae and other small invertebrates. Males are aggressive and will attack fish larger than itself, slashing its prey with its sharp teeth and devouring it when it is subdued. Breeding takes place in shallow water between April and September, the males competing fiercely for the females. A few eggs are spawned at a time, and these are fertilised by the males which grasp the females with their fins. The eggs clump together and sink to the seabed, connected by sticky threads. They hatch after five or six days. During the winter, this fish burrows into the soft substrate and remains dormant.

The Leon Springs pupfish (Cyprinodon bovinus) is a species of fish in the family Cyprinodontidae. It is endemic to Pecos County, Texas in the United States. It is a federally listed endangered species.

The Leon Springs pupfish is found at the shallow edges of spring-fed wetland pools, where it is most frequently observed in areas without vegetation. Its diet consists of diatoms, amphipods, and ostracods.

The Devils Hole pupfish (Cyprinodon diabolis) 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 (C. salinus). 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.

Devils Hole is more than 130 m (430 ft) deep, though pupfish are only found in the upper 24 m (80 ft). The water is a constant temperature of 33 °C (91 °F) and dissolved oxygen levels are low. A small, shallowly submerged rock shelf provides critical feeding and spawning habitat for the pupfish. Nearby agricultural irrigation in the 1960s and 1970s caused the water to drop in Devils Hole, resulting in less and less of the shelf remaining submerged. Several court cases ensued, resulting in the Supreme Court case Cappaert v. United States, which determined that the preservation of Devils Hole as a National Monument in 1952 implicitly included preservation of adequate groundwater to maintain the scientific value of the pool and its fauna. Other threats faced by the species include flash floods, earthquakes, and vandalism.

Taxonomy and evolution

The Devils Hole pupfish was described as a new species in 1930 by American ichthyologist Joseph H. Wales. The holotype had been collected by Wales and George S. Myers in March 1930 at Devils Hole in the US state of Nevada. The species name "diabolis"was chosen to allude to the type locality of Devils Hole. Both the species name and the location spell"Devils Hole"without an apostrophe, a relic of the"quirks of government cartographers and scientists". According to genetic analysis, the sister taxon of the Devils Hole pupfish is Cyprinodon nevadensis. Along with the Death Valley pupfish (C. salinus), the three Amargosa River basin species form a clade.

The age of the species is subject to considerable debate, with analyses recovering starkly different figures. Devils Hole was formed around 60,000 years ago, with some researchers assuming the pupfish has existed in isolation for 10,000 – 20,000 years. How it colonized Devils Hole is unknown; hypotheses include arriving via subterranean waters or over dry land. As Native Americans used pupfish species as food, it has been speculated that they introduced the pupfish to Devils Hole, intentionally or not. Its divergence from a common ancestor with C. nevadensis mionectes was estimated at 217 – 2530 years in one study. Two studies, each based on independent genetic datasets, estimated that this species may have first colonized the hole within the past 1,000 years, but another suggested the species is as old as 60,000 years. These estimates depend heavily on knowledge of the mutation rate in this species, which is unknown, but is predicted to be one of the highest for any vertebrate due to its small population size.

Description

The Devils Hole pupfish is the smallest pupfish species in the genus Cyprinodon, with lengths up to 30 mm (1.2 in). The average length is 23 mm (0.9 in). Males and females differ in coloration. Males are overall dark brown with metallic blue on their sides. The margins of all fins are black, and the back has golden iridescence. Iridescence is particularly pronounced on the opercles (gill covers) which have a violet sheen on their posterior side. The iris is blue and also iridescent. Females and young are more yellow in color than the males. Females have yellowish-brown backs, and the margins of their pectoral and caudal fins are yellow, not black. The dorsal fin has a black margin like the males, however. Females' opercles are metallic green, and their eyes are tinted metallic blue. The young are overall colored as the females, though they have a faint vertical bar on their sides.

Individuals lack pelvic fins, though have been observed to grow them when raised in lower temperatures in captivity. Its dorsal fin has twelve rays, while each pectoral fin has seventeen rays. The caudal fin is convex in appearance and has twenty-eight rays, curving outward at the margin. Its lateral series (the number of scales from the back end of the opercle to the beginning of the tail) is twenty-seven scales. The scales are ctenoid, or toothed, on the outer margin.

Biology and ecology

The Devils Hole pupfish consumes a variety of food items representing nearly all possible food resources in Devils Hole. Its food resources include inorganic particulate matter; the algae Spirogyra and diatoms; the freshwater crustaceans Hyalella azteca and ostracods; protozoa; the beetle Stenelmis calida; the flatworm Girardia dorotocephala; and the freshwater snails Tryonia. The consumption of the various food resources varies seasonally, though inorganic particulate matter had a high frequency of occurrence in stomach contents year-round in one study. The inorganic particulate matter consists of primarily travertine, a form of limestone. The three most common food items for each season by frequency of occurrence were:

As Spirogyra was mostly found undigested in the stomach, the authors hypothesized that it was not important as a food resource, but rather as a foraging substrate. The inorganic particulate matter was thought to be incidentally consumed as well as a result of the fish's foraging strategy of bottom feeding and surface feeding.