Fundulus luciae

Spotfin killifish
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Cyprinodontiformes
Family:	Fundulidae
Genus:	Fundulus
Species:	F. luciae
Binomial name
Fundulus luciae (S. F. Baird, 1855)
Synonyms
Hydrargyra luciae (Baird 1855)

The spotfin killifish (Fundulus luciae) is a member of the genus Fundulus. This hardy fish is notable for spending its entire life in sporadically flooded salt marsh habitat, sheltering in shallow pools, puddles, and small tidal rivulets.^[1] It closely resembles the mummichog (Fundulus heteroclitus) in shape and coloration, but the two species can be distinguished by dorsal fin ray count: 8–9 in the spotfin versus 11–12 in the mummichog.^[2] Additionally, the dorsal fin of F. luciae originates farther back, and slightly behind the anal fin origin; in the mummichog, the dorsal fin begins anteriorly to the anal fin origin.^[3] The spotfin killifish is named for the pronounced ocellus found on the posterior dorsal fin of adult males. It is a small fish, seldom attaining 50 mm in total length.^[4] Its distribution extends along the U.S. east coast from Massachusetts^[5] to Georgia.^[6]

Taxonomy

Fundulidae (Order: Cyprinodontiformes) is a family of topminnows, or killifishes, that are found in freshwater, marine, and brackish habitats in North America, Bermuda, and Yucatán.^[7] "Topminnow" was coined following observations of fishes using aquatic surface respiration (ASR), a behavior used to acquire more oxygen by hovering parallel to the surface near the air-water interface, during periods of hypoxia.^[8] The characteristic upturned mouth and flattened head of fundulids is believed to enhance ASR in low oxygen conditions.^[8] Interestingly, the scientific name Fundulus means exactly the opposite. Fundus is Latin for "bottom,"^[9] and probably refers to the muddy substrate many common species inhabit and the propensity for fish to hide from predators in sediments. Killifish derives from the Dutch word "kill," meaning a stream or brook; it is a general name given to egg-laying toothcarps.^[10]

The genus Fundulus contains 38 extant species, found along U.S. coastal and inland regions, Bermuda, Cuba, and Yucatán.^[7] Luciae comes from the Latin word for "light," probably referring to silvery, iridescent qualities of the fish's body. The spotfin killifish was initially described as Hydrargyra luciae in 1855 by SF Baird–"hydrárgyros" is a Greek word for mercury.^[11]

Description

Fundulus luciae male, from Fishes of the Chesapeake Bay by Murdy, Birdsong, and Musick

The spotfin killifish is the smallest member of its genus,^[12] rarely exceeding 50 mm total length^[4] or 40 mm standard length.^[1] Larval fish transition to juvenile stage at around 10 mm standard length.^[13] Sexual maturity is attained at approximately 24–27 mm TL (males) and 28–30 mm TL (females).^[1] Body shape is elongated and less stocky than the mummichog, with an upturned mouth, flattened head and rounded caudal fin. Adults are sexually dimorphic, although both sexes are darker on top with a lighter belly.^[2] Juveniles and adult females are similar in appearance, with a body that is grayish-green to olive green in color, lacking a dorsal ocellus, and generally without vertical bars,^[1][14] although females may sometimes have sidebars (usually faint).^[15] Mature adult females may also have a visible sheath of tissue along the front of the anal fin, which is believed to function as an oviduct.^[14] Adult males have 10–14 dark vertical bars and the eponymous dorsal ocellus.^[1][2][14] During spawning season males develop dramatic coloration, consisting of vivid yellow-orange pigment extending over the belly, pelvic and anal fins, caudal peduncle, and caudal fin.^[1] Breeding males may also develop contact organs–small fleshy protuberances–on the head, sides of the body, and medial fins.^[1] Dorsal fin rays number 8–9 (usually 8) which is different from the mummichog, which has 11–12 dorsal fin rays.^[2] The anal fin has 10 rays. The spotfin's dorsal fin originates posteriorly to the anal fin origin.^[16] Longitudinal scale rows number 34–36.^[2] The gill opening is restricted superiorly.^[2]

Distribution and habitat

The spotfin killifish inhabits salt marshes from the upper edge of the regularly flooded zone, characterized by Spartina spp.(cordgrass), into the irregularly flooded marsh, characterized by Juncus roemarianus (needlerush), where it shelters in puddles, shallow pools, small tidal rivulets, culms at the base of plants, and even crab burrows.^[1][2][13] It is a permanent resident of the emergent marsh and remains even at low tide.^[1][13] It prefers muddy substrate, probably because mud retains water at low tide more effectively than sand. Spotfins are euryhaline but prefer medium to high salinities.^[17]

Spotfin killifish are distributed along the east coast of the United States, ranging from Massachusetts^[5] to Georgia.^[6] Previously reported as "rare or infrequently encountered,"^[15][16] subsequent efforts have continued to document new populations within the established range and revealed that spotfin killifish can be relatively abundant when sampled in appropriate habitat.^{[1][18][19][20]}

Conservation Status

The spotfin killifish is listed as a species of "least concern" (LC) by the IUCN Red List of Threatened Species.^[21]

Diet

Spotfin killifish have a diet similar to the mummichog, consisting of detritus, diatoms, foraminiferans, rotifers, insects (dipterans–including mosquitoes and larval chironomids, homopterans, coleopterans, hymenopterans, lepidopterans, odonates, and hemipterans), collembolans, arachnids (spiders, pseudoscorpians, and acarina), crustaceans (copepods, tanaids, ostracods, cladocerans, isopods, and amphipods), annelid worms, mollusks (gastropods), and fish eggs.^[1][14]

Physiology

Hardiness

Fundulids in general are known for high tolerance to

References