Rainwater Killifish, Lucania parva
Rainwater Killifish, Lucania parva. Fish caught from coastal waters off Punta Gorda, Florida, February 2017. Length: 5.1 cm (2.0 inches). Catch, photograph and identification courtesy of George Brinkman, Guelph, Ontario, Canada.
Rainwater Killifish, Lucania parva. Fish caught from a freshwater pond in the greater Pensacola area, Pensacola, Florida, June 2023. Length: 5.1 cm (2.0 inches). Catch, photograph and identification courtesy of Chris Moore, Peoria, Arizona.
Rainwater Killifish, Lucania parva, Female. Fish caught from within the Ocala National Forests, Ocala, Florida, August 2019. Length: 5.1 cm (2.0 inches). Catch, photograph and identification courtesy of Luke Ovgard, Klamath Falls, Oregon.
Rainwater Killifish, Lucania parva, Male. Fish caught from an irrigation canal in the greater Orlando area, Orange County, Florida, August 2019. Length: 5.1 cm (2.0 inches). Catch, photograph and identification courtesy of Luke Ovgard, Klamath Falls, Oregon.
The Rainwater Killifish, Lucania parva, is a member of the Pupfish or Cyprinodontidae Family, and is known in Mexico as sardinilla de llavia. Globally, there are three species in the genus Lucania, of which two are found in Mexican waters, one in interior freshwater systems and one along coastal waters of the Atlantic Ocean.
The Rainwater Killifish has a deep, compressed body that have a depth that is 4X standard length with a small, flattened head with a blunt snout, large eyes, and a subterminal, oblique small mouth with a protruding jaw that is equipped with a single row of hooked teeth. They are a small silvery fish with yellow flecks. Their back is silvery to light green, with a narrow dark middorsal stripe. They have less than 30 large, dark-edged lateral line scales on their back and sides that create a cross-hatched pattern. Their head is covered with speckled melanophores. They are silver ventrally. Their fins lack pigmentation except for some melanophores along the rays. Breeding males have a black anterior blotch on the dorsal fins and dark bands at the base and the margin that include orange pigmentation, and males develop prickly contact organs to the top and sides of the head and side of the body between the anal and dorsal fin bases. Their anal, caudal, pectoral, and pelvic fins are rounded with red to orange with black margins. Their anal fin has 8 to 13 rays with the 3rd ray branched; their caudal fin is rounded; their single dorsal fin has 9 to 14 rays and it has a short base, rounded and set in front of the anal fin and behind the pelvic fin; their pectoral fins have 10 to 15 rays with a narrow base and inserted low on the side; and their pelvic fins have 5 to 9 rays and are inserted well behind the pectoral fins. They have 5 to 9 short gill rakers. They are covered with smooth scales. Their lateral lines are reduced to a series of pits along the sides.
The Rainwater Killifish are found in large schools in vegetated quiet water primary in salt marshes, bays, lagoons, brackish stretches of coastal streams, and in freshwater lakes and rivers over sand and mud substrate at depths up to 2 m (7 feet) with temperatures between 10oC (50oF) and 25oC (77oF). They can tolerate high salinity waters and changes in salinity. They reach a maximum of 6.2 cm (2.4 inches) with females being larger than males. They consume larval crustaceans, mosquito larvae, small worms, and mollusks. They are known to provide cleaner services of other fishes consuming parasites. They are a key component of the food web in coastal marshes being preyed upon by fish, birds, and mammals. They are known to make seasonal migrations indicative that the species is anadromous, moving into lower salinity water for breeding, and returning to higher salinity water after breeding. Reproduction is oviparous with spawning occurring in heavily vegetated areas where each female releases 7 to 46 eggs that fertilized externally by the males. The eggs are sticky and attach themselves to plant materials. Each female can produce more than one brood per year.
The Rainwater Killifish is a resident of Mexican waters of the Atlantic Ocean but has a limited distribution being found in coastal tidal pools and within the freshwater systems that drain into the Gulf of Mexico from the Texas boarder south and east to northern Yucatán.
The Rainwater Killifish is similar in stature, and easily confused, with the mosquitofishes but they lack the modified anal fin found in the male mosquitofishes and the females have a branched third anal ray absent in the female mosquitofishes. They have dorsal fins that are found before the anal fins which differentiates them from livebearers. They are one of few killifish that lack bars.
From a conservation perspective the Rainwater Killifish are currently considered to be of Least Concern with stable, widely distributed populations. They have been introduced for mosquito control to many areas along the northern coast of the Gulf of Mexico where they quickly became highly invasive dominating native species. They have been accidently introduced in many areas as contaminants of Largemouth Bass and Gambusia introductions and by aquarium releases. They are small in stature and of limited interest to most. They are utilized by the aquarium trade but are difficult to maintain.