Gulf Killifish

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Gulf Killifish, male.
Photos by Gretchen Grammer.

Description

The Gulf killifish has a distinctive blunt head, stout body and short snout. The lower jaw projects slightly beyond the upper jaw. The caudal peduncle is relatively deep. (The caudal peduncle is the portion of the body behind the rear-most fins and just ahead of the tail.) There is only one dorsal fin and none of the fins have spines.

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Gulf Killifish. Base image is female. Mouse over image to see male.
Photos by Gretchen Grammer.

Gulf Killifish have grey or greenish backs and pale or yellowish undersides with numerous irregular small pale or pearly spots, mottling, and faint bars.  The overall coloration is pale grey, light bronze, or olive. Females and juveniles are relatively drab, as are non-breeding males. But during the breeding season, males become quite colorful. Their backs become darker and bluish, with glittering spots on the body. The tail, anal fin, and dorsal fin show a blue tint with light blue spots and yellow-orange edges.  The pectoral and pelvic fins are yellow orange, particularly the edges. Some individuals develop orange-red anal fins with red spots. Red spots may also be present on the tail.

The maximum length of Gulf Killifish is typically described as about seven inches. However, Dr. Richard Heard, Professor of Invertebrate Zoology at GCRL, captured nine to ten inch specimens in isolated salt ponds at St. Marks, Florida. The large individuals had been feeding on Gulf Killifish.

There are two subspecies. Fundulus grandis grandis occurs along the Gulf coast from Veracruz, Mexico to southwestern Florida.  Fundulus grandis saguanus inhabits the Florida Keys and Cuba.

Similar Species

The Gulf Killifish, particularly young fish, may potentially be confused with a number of species of topminnows and other killifish. However, the blunt head and deep caudal peduncle of larger adult Gulf Killifish are good identifiers. The Gulf Killifish is the largest of the eight species of killifish in the Gulf states. Any killifish longer than three inches that lacks bars on its sides is likely to be a Gulf Killifish.

The mummichog, Fundulus heteroclitus, is a similar species that inhabits the Atlantic coast

Occurrence

The natural range of the Gulf Killifish includes coastal waters and their tributaries from the St. John's River on Florida's Atlantic coast to the Florida Keys and across the coast of the Gulf of Mexico to Veracruz, Mexico and Cuba. It has been introduced to Hawaii, New Mexico, and Texas; it thrives in Texas rivers as far as 250 miles from the coast. Gulf Killifish have been considered invasive after introduction in some locations and dominating native species.

Killifishes are primarily estuarine, living in marshes, seagrass beds, oyster beds, and other low-salinity habitats. Gulf Killifish are extremely tough and hardy. They tolerate low oxygen levels and a wide range of salinity, from fresh water to tidal pools saltier than the open ocean. They survive water temperatures from 32°F (0°C) to 94°F (35°C).

Life Cycle & Reproduction

In the northern Gulf, Gulf Killifish spawn from March to September, with a major peak during March and April and a lesser peak during August and September. Spawning takes place in shallow water, usually in dense beds of marsh grass. The male fish corners the female in a clump of vegetation, among oysters or debris, on in mud at the water's edge and clasps her with his fins. They are batch spawners and spawn dozens of times during the season.

The eggs of the Gulf Killifish are capable of enduring and hatching under the substantially varying temperature and water level found in their marsh habitat. Some eggs remain continuously immersed until hatching, adhering to marsh grass and debris in the water column or near the muddy bottom. However, eggs laid during the highest tides may adhere to marsh grass near the surface and be exposed to air for most of their incubation period. The eggs survive air exposure and hatch when the next high tides occur about two weeks later. Gulf Killifish eggs hatch in ten days to three weeks, depending on water temperature, with the shorter times occurring in warmer water.

Compared to many other species, Gulf Killifish egg production is rather low. In aquarium studies, females were found to deposit about 20 eggs per day in a three-day cycle. Other studies suggest a rate of about 80 eggs per day over a five day period, with an annual total of 872 to nearly 13,000 eggs per year. Fertilized eggs are about 0.01 to 0.114" (2.6 to 2.9 mm) in diameter. For comparison, the diameter of a standard BB is roughly half again as large, about 0.172" (4.35 mm).

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Gulf Killifish.
Photo by Mike W. Howell and Ronald L. Jenkins, Samford University. Click for larger image.

Gulf Killifish reach sexual maturity in as little as three to four months. Most fully grown fish reach a length of three to four inches. Females are typically larger than males.

Diet

Gulf Killifish are omnivorous and feed aggressively throughout the water column. They consume a variety of algae and vascular plants. Their animal prey ranges from tiny copepods and mosquito larvae and pupae to mollusks, other insects, grass shrimp, fiddler crabs, and small fishes. Their diet varies with the water level as the tides change, with more insects being taken at higher water levels.

Gulf Killifish are important predators of mosquitos, primarily as larvae and pupae. Gulf Killifish have been introduced for biocontrol of mosquito populations, though the eastern and western mosquitofish (Gambusia holbrooki and Gambusia affinis) are more commonly used.

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Gulf Killifish.
Photo by Ash Bullard, Auburn University. Click for a larger version.

Predators, Parasites, and Other Threats

Gulf Killifish are a key part of the food web in coastal marshes. They are preyed upon by a variety of other species throughout their entire life cycle, including fish, birds, and mammals.

The severe winter of 2013-2014 and fast temperature drops resulted in substantial mortality among Gulf Killifish on the Mississippi coast. Research at GCRL has shown that cold kill events may be exacerbated by damage to the liver and pancreas by single-cell parasites that probably affect the entire adult population of Gulf Killifish in the mainland coastal marshes.

Gulf Killifish are are connected to coastal marsh ecosystems not only with respect to the food web, but as a host for various parasites. Killifish provide an intermediate host for several flatworm and roundworm parasites that also rely on wading birds or marsh dwelling mammals, such as raccoons, at other life stages.

Populations of Gulf Killifish are capable of recovering quickly from stresses.

Live Bait for Fishing

Gulf Killifish are a very popular live bait for speckled trout, red drum, flounder, and other inshore fish. The species is ideal for live bait fishing. They are hardy and active, they tolerate extreme conditions, and they have no spines to make them difficult to handle.

Use in Oil Spill Research

Gulf Killifish have long been used in toxicity testing. The species is attractive as a test subject because they are abundant, widespread, hardy, remain in a limited area, and comprise a key part of the food web of coastal marshes. Gulf Killifish are now being used in several research projects evaluating the effects on coastal marsh ecosystems of BP's Deepwater Horizon Oil spill and the use of dispersants in the response.

Dr. Robert J. (Joe) Griffitt, Assistant Professor of Toxicology at GCRL, is co-principal investigator on a Gulf of Mexico Research Initiative research project titled "The Combined Effect of Environmental and Anthropogenic Stressors on Fish Health." The project will characterize the effects of PAH compounds found in crude oil on Gulf Killifish under various environmental conditions throughout their life stages and use the information obtained to develop a population model for predicting the consequences of PAH exposures. The Gulf Killifish was chosen as study subject and potential sentinel species because of it's presence in coastal marshes across the entire northern coast of the Gulf of Mexico.

Aquaculture

Though most commercial bait dealers rely on wild caught fish, aquaculture techniques for Gulf Killifish have been well researched and commercial operations are developing.

Resources and References

Gulf Killifish Videos

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Gulf Killifish eggs hatching (under the microscope), Youtube, 1 min., 35 sec.