The rainwater killifish is a small silvery fish with yellow flashes and diamond shaped scales that is widespread from Cape Cod, Massachusetts, through to Tampico, Mexico. It is commonly found in large numbers in fresh to brackish estuarine environments. It feeds on tiny crustaceans, mosquito larvae, small worms, and mollusks. It can reach up to 62 mm.
Description
Coloration: Body not barred. Back silvery to light green, with a narrow, dark middorsal stripe. Scales on sides outlined in melanophores, creating cross-hatched pattern, which is especially prominent in breeding males. Forward and upper surfaces of the head speckled with melanophores, which also extend onto the underside of the lower jaw. Belly and undersides of body are silver. Fins generally lack pigmentation, except for some melanophores along the rays. In breeding males, dorsal fin has a black anterior blotch and dark marginal and basal bands that may include orange pigmentation. Caudal, anal, and pelvic fins red to orange, with black marginal bands. Counts: 10+ dorsal fin rays; 8-13 scale rows from pelvic origin to isthmus; 30 or fewer longitudinal scale rows ; 27 lateral scales; 11 dorsal fin rays; 13 pectoral fin rays; 6 pelvic fin rays; 9 anal fin rays; 16 caudal fin rays; 8 gill rakers on 1st arch. Body shape: Body deep, rather compressed; head flattened above, tapering to vertically rounded, blunt snout. Body depth contained four times in standard length. Body axis straight. Mouth position: Supraterminal, oblique; mouth small; obliquely sloped, protruding lower jaw . External morphology: Distance from origin of dorsal fin to end of hypural plate more than distance from origin of dorsal fin to preopercle ; dorsal and caudal fins rounded; pectorals, pelvic, anal fins rounded at apex. Males develop prickly contact organs on top and sides of head and on side of body between dorsal and anal fin bases. Female with membranous sheath surrounding genital opening. Internal morphology: Teeth conical and simple. Premaxillary and mandibular teeth uniserial or irregular, occasionally with a few strong inner teeth.
Diet
Simpson and Gunter and Harrington and Harrington reported diet items including larval crustaceans, mosquito larvae, small worms, and mollusks. Harrington and Harrington noted that the species heavily predates both larvae and pupae of saltmarsh mosquitoes.
Habitat
Found in salt marshes, bays, and lagoons from Cape Cod, Massachusetts to Tampico, Mexico ; common in freshwaters of St. John's River system, Florida, and Rio Grande and Pecos River in Texas and New Mexico. Lucania parva is a schooling species.
Spawning season: In Texas, females began ripening in February, and a few were gravid in July; peak spawning in May and June ; may occur in earlier in the spring . Sublette et al. reports spawning in New Mexico from spring – fall, at least in southern portion of state. Spawning location: During spawning, male and female swim into vegetation with fine leaves; there eggs are released and fertilized; eggs have mucous threads with which they are attached to plant material. McLane noted that male courtship behavior was observed near clumps of Naias and Vallisneria. Reproductive strategy: A courting male swims in loops slightly below the female, waiting for the female to respond by stopping; after a female stops, the male moves under her flicking his head against her throat; pair moves slowly toward surface of the water, while male continues to rub his head against underside of the female; when they are near surface, female swims into vegetation having fine leaves or algal masses, and the male follows; using his dorsal and anal fins, the male then clasps female, and eggs are released and fertilized. Fecundity: 7-46 ripe ova plus numerous smaller ova ; maximum reported count 104. Freshly laid eggs are spherical, nearly colorless, having chorionic threads; live eggs averaging 1.23 mm in diameter; eggs hatch in 6 days at water temperature of 23.9 degrees C. More than one brood may be produced per year by a single female.
Distribution
Native to coastal waters from Massachusetts to Tampico, Mexico. Introduced into California, Nevada, Oregon, and Utah. Locally abundant in lower Pecos River drainage, New Mexico, not ascending tributary streams far above mouth.
