Lucania parva
(rainwater killifish)

Lucania parva, commonly known as rainwater killifish, is a small silver to olive green fish which occurs frequently in estuarine waters along the Atlantic and Gulf of Mexico coasts of North America. Inland populations are common in freshwater rivers of Florida and freshwater to saline waters of the Rio Grande drainage in New Mexico and Texas. Populations were incidentally introduced west of the Rocky Mountains via stocking of oysters and freshwater sportfishes (Hubbs and Miller, 1965). To date, L. parva does not seem to be expanding rapidly beyond its initial point of introduction.

Native range of L. parva extends along Atlantic and Gulf of Mexico coastal drainages of North America from Massachusetts, USA, to Quintana Roo, Mexico (Hubbs et al., 2008). L. parva is typically restricted near coastal waters in saltwater, brackish, and freshwater habitats, although extending considerable distances upstream within freshwater rivers of Florida (Fuller and Noa, 2008), New Mexico, and Texas (Hubbs and Miller, 1965). Native status is assumed within inland waters of the San Antonio River (Hubbs et al., 2008) and Rio Grande drainage, including the Pecos River (Hubbs and Miller, 1965). Sublette et al. (1990) considers L. parva native to the Pecos River in New Mexico but introduced into the Rio Grande of New Mexico.

Introduced populations are reported in several Atlantic, Gulf of Mexico, and Pacific drainages of USA.

Introductions are attributed primarily to contaminated stocks of oysters and sportfishes, based on 1870-1960s protocols for transplanting organisms. Current stocking protocols and governmental oversight minimize the risk of future L. parva introductions.

L. parva associates with vegetated areas (Jordan, 2002) in brackish ponds and sloughs of bay systems and is less abundant in salt flats and bay shorelines (Gunter, 1950). In Texas, USA, L. parva is locally abundant (>45% in relative abundance) in saline reaches (>10,000 µS/cm) of the Pecos River and associates with slackwater habitats, vegetation, and silt substrates. Though some tributaries and mainstream reaches of the Pecos River are naturally saline, stream flow modifications and water diversions contribute to greater salt content in portions of the mainstem Pecos River by removing freshwater inflows before reaching the naturally occurring saline zones and therefore leaving the salt water springs as the primary base flow (Hoagstrom, 2009). L. parva and other euryhaline fishes are the dominant forms in the now hyper saline reach of the Pecos River before freshwater inflows from Edwards-Trinity aquifers dilute saline waters in the lower canyon reach of the Pecos River.

Genetics

Berdan et al (2014) assessed genomic architecture of sister taxa L. parva and Lucania goodei. Carson et al. (2015) assessed mDNA diversity with sister taxa Lucania interioris.

Reproductive Biology

Potentially an anadromous species, L. parva move to more saline waters during non-breeding season in the autumn (Hardy, 1978) and into less saline waters during breeding season in spring and summer (Foster, 1967) in the USA. Breeding season might begin as early as February within Texas estuaries and extend into July (Gunter, 1950; Simpson and Gunter, 1956). In inland waters of New Mexico, breeding season is from spring through autumn (Sublette et al., 1990). Males court females with a variety of physical displays (e.g. swimming in loops around the female, rubbing of the female abdomen with his head) near vegetation (McLane, 1955; Foster 1967). Females deposit ova (mean=25 (McLane, 1955); up to 104, (Hildebrand and Schroeder, 1928; Hardy, 1978)) with mucous filaments to aid in attaching on vegetation (Foster, 1967). The courting male deposits sperm. Males and females spawn multiple times during the breeding season (Hardy, 1978). Eggs hatch within 6 days (Foster, 1967). Age-0 fish become sexually mature within 3-5 months at a size of 25 mm in total length (Hildebrand and Schroeder, 1928).

Longevity

Likely 1-2 years.

Population Size and Density

L. parva is rare <0.1% in relative abundance) in San Francisco Bay (Matern et al., 2002). Abundant (>45% in relative abundance) in portions of the Pecos River (T. Bonner, Texas State University, USA, author’s unpublished data).

Nutrition

Primarily a pelagic and surface feeder, L. parva feeds crustaceans (subclass Copepoda) and dipterans, especially mosquito (Family Culicidae) larvae and pupae (Simpson and Gunter, 1956; Harrington and Harrington, 1961). They can consume small annelids and molluscs (found in one stomach each; Simpson and Gunter, 1956).

Environmental Requirements

L. parva is a euryhaline species, generally taken from estuarine waters ranging from 0.7-24 ppt (Gunter, 1950; Miller and Guillory, 1980). In a Mississippi estuary, USA, L. parva were more associated with sites near salinities at 4 ppt than sites with lower and greater salinities (Peterson and Ross, 1991). The species has however been collected from full strength seawater (32 ppt) and found surviving at 60 ppt during a dry-down event (Rebecca Fuller, personal communication).

A self-sustaining population exists within freshwaters (800-1,375 mS/cm) of Independence Creek, a tributary of the Pecos River in Texas, USA (Bonner et al., 2005; Watson, 2006). Large numbers of L. parva were taken from the Pecos River at water temperatures of 32°C.

Introduced and native populations co-exist with a large number of predatory organisms (e.g. bass, sunfishes, catfishes, and reptiles). L. parva are likely preyed upon by wading birds, since fundulids, in general, are a major food sources for wading birds (Kneib, 1982).

L. parva is sufficiently distinct and detectable among sportfish. Eggs and larvae on vegetation or oysters are distinct with close inspection.

Members of the Family Fundulidae are typically distinct from other families within Order Cyprinodontiformes. However, L. parva, with silvery to light green color, scales outlined with pigments, and lacking lateral bars, resembles Gambusia (Poeciliidae).

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Prevention

Public awareness

Public awareness is important in preventing establishment of new populations and further introductions of L. parva.

Eradication

Eradication efforts are not known to be underway at this time.

Control

Physical/mechanical control

High relative abundances at some locations, along with eggs attached to substrate, likely preclude successful control by physical/mechanical methods.

Chemical control

Piscicide, such as rotenone, likely is effective to control and eradicate in small water bodies.

Lingering questions exist about native status of L. parva in inland waters of the Rio Grande in New Mexico, USA. Information is lacking on the effects of L. parva on native species within inland waters and Pacific coast waters.

07/042016 Original text by:

Timothy Bonner, Texas State University, USA