Fundulus heteroclitus

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Geographic Range

Fundulus heteroclitus, a species of killifish commonly known as the mummichog, occurs along the Atlantic coast of North America. They extend from the Gulf of St. Lawrence all of the way to the gulf coast of Texas. The waters of Sable Island, southeast of Halifax, Canada, has also been known to be inhabited by Fundulusheteroclitus. These remarkable fish also live inland in tidal creeks and lagoons (Rutherford, 1996).

Habitat

Tidal creeks are the habitat of choice for Fundulus heteroclitus. They are also found in saltwater marshes, estuaries, and in sheltered shores where tides flow over eelgrass. The common feature between all of these habitats is that there is submerged vegetation where the fish can spawn and feed (Rutherford, 1996).

Fundulus heteroclitus is a remarkable fish. It has proven to be one of the most hardy and adaptable fish known. Most fish cannot survive for any period of time in waters as warm as 34° C. However, the mummichog can survive in this temperature for up to 63 minutes before falling victim to heat shock. It can also withstand temperature fluctuations from 6° C to 35° C (Abraham, 1985).

The mummichog also has a great tolerance to changes in salinity. Some mummichogs, such as the ones inhabiting the Chesapeake Bay area, prefer to live in freshwater and rarely, if ever, find themselves in salt water. Other mummichogs live along the coast in bays filled with seawater. The fish's upper limit for salinity is 106 - 120.3 ppt, while the average salinity of sea water is 32-33 ppt. This demonstrates the huge range of salinities that the mummichog can survive in (Abraham, 1985).

Physical Description

As adults, Fundulus heteroclitus range between 12.7 and 17.8 centimeters in length, the females growing larger than the males. They have flattened heads and the mouth is turned upward, clearly an adaptation to feeding at the surface of the water. This attractive fish is dimorphic, meaning that males and females have different physical characteristics. The males are darker in color than the females and exhibit blue or orange markings during the breeding season (Save the Bay, date unknown). Males are dark olive green on the dorsal side and lighter yellow on the ventral side. They also display vertical stripes along their sides. Females are silverish yellow on the ventral side and that color gradually fades to a more distinct yellow on the dorsal side. They also lack the stripes that male Fundulus heteroclitus display. All Fundulus heteroclitus have a single soft dorsal fin and their pelvic fins are located close to the rear fin (National Oceanic and Atmospheric Administration Coastal Services Center, 2001).

Reproduction

The breeding patterns of Fundulus heteroclitus have been studied intensely. Fundulus heteroclitus have the ability to spawn up to eight times in one season (Rutherford, 1996). During spawning season, males become increasingly aggressive and they begin to display bright colors on their rear fins and bright spotting along the sides of their bodies. The spawning season begins in the spring and lasts until fall. Spawning takes place when the tides are highest during the new or full moon. This is because the eggs develop out of the water. They are laid on almost any surface around the spawning site. Common places for mummichog eggs are in empty mussel shells, on aquatic plants, in pits dug and covered by the female, and even directly on the bottom. The eggs are laid in the shallow area during high tide so when the tide goes out, they will be exposed to the air in which they develop. After the following monthly high tide, they are submerged in water again and begin to hatch (National Oceanic and Atmospheric Administration Coastal Services Center, 2001). This process takes approximately 24 days to complete. Females can release up to 460 eggs at one time and when the eggs are released, they affix themselves to whatever object they first contact (Government of Newfoundland and Labrador, date unknown).

When hatched, the larva of Fundulus heteroclitus are approximately seven millimeters long. They remain in the intertidal zone for six to eight weeks after hatching. Here they live on the outskirts of the marsh during high tides and in shallow pools during low tides. Once the larva are about 15-20 mm in length, they begin to move and swim with the adults in schools. When tides are low, these juveniles no longer stay in the shallow pools but move to subtidal marsh creeks and deep intertidal pools. Full physical maturity is reached in about two years (Rutherford, 1996).

Behavior

Another common name for Fundulus heteroclitus is the mud minnow. This name originates from its method of avoiding freezing during the winter months. When winter arrives, mummichogs burrow their way into the sediment and mud at the bottom of their habitat. Mummichogs have been found to burrow themselves up to 20.3 centimeters deep in the mud (Save the Bay, date unknown). Despite this extraordinary ability, not all mummichogs opt for this survival mechanism during the freezing months. Some move to deeper waters, often at the mouths of channels where the constantly moving water will not freeze (National Oceanic and Atmospheric Administration Coastal Services Center, 2001). When mummichogs choose to burrow for the winter they will remain buried in the mud until a suitable temperature of 15° C is reached in the spring. At this point, the fish will push their way back to the surface and breeding season will begin. During the warm months Fundulus heteroclitus are relatively stationary fish. Most of them will not leave a range of about 38 meters along the shoreline in tidal creeks (Rutherford, 1996).

The word "mummichog" comes from an Indian word which means "going in crowds." This is exactly what Fundulus heteroclitus do. They travel in massive schools, often times with their numbers exceeding several hundred (Rutherford, 1996).

Breeding behavior in mummichogs starts when the females have ripe ova. One technique that the females use to attract mates is lying on their sides and displaying their silvery bellies. Other times, a male and female will swim in tandem before mating, the female slightly above and ahead of the male. Eventually, the male will force the female onto a structure, such as a plant, rock, or empty shell, and the two will release their gametes (Abraham, 1985).

Communication and Perception

Food Habits

Mummichogs primarily feed at the surface of the water (Government of Newfoundland and Labrador, date unknown). This feeding occurs predominantly at high tide during the daytime. They are however somewhat opportunistic feeders and will feed at all levels of the aquatic zone as long as there is food available. Mummichogs feed on a large variety of organisms. Some of the things that they eat include phytoplankton, mollusks, crustaceans, insect larvae, eggs of their own species, and vegetation such as eel grass. These fish have also been known to eat other smaller fish (Rutherford, 1996).

Economic Importance for Humans: Positive

This fish preys on mosquito larvae and is therefore occasionally used instead of harmful pesticides to control mosquito population. They are an extremely important food source for many larger fish, which are valuable commercially, and for wading birds and seabirds (National Oceanic and Atmospheric Administration Coastal Services Center, 2001). For some of these birds mummichogs compose up to 95% of their entire diet. One final economic value of the mummichog is its use as bait for recreational fishing (Abraham, 1985).

Economic Importance for Humans: Negative

Not available.

Conservation Status

Contributors

Michael Paesani (author), Western Maryland College, Randall L. Morrison (editor), Western Maryland College.

Glossary

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

tactile

uses touch to communicate

References

Abraham, B. Jun. 1985. Species Profiles: Life Histories and Environmental Requirements of Coastal Fishes and Inveratbrates: Mummichog and Stripes Killifish. Biological Report, 82: 1-14.

Government of Newfoundland and Labrador, date unknown. "Mummichog: Fundulus heteroclitus" (On-line). Accessed 4 May 2001 at http://www.gov.nf.ca/forest/wildlife/ourwldlife/animals/inlandfish/mummichog.htm.

National Oceanic and Atmospheric Administration Coastal Services Center, 8 Feb. 2001. "ACE Basin Species Gallery: Mummichog" (On-line). Accessed 4 May 2001 at http://www.csc.noaa.gov/acebasin/specgal/mummicho.htm.

Rutherford, R. 22 Jan. 1996. "Environmental Habitat Quality Requirements / Guidelines for Mummichog" (On-line). Accessed 4 May 2001 at http://www.kayhay.com/shelburne/mummicho.htm.

Save the Bay, date unknown. "Save The Bay’s KIDSWEB: An inside peek at the mummichog (killifish)" (On-line). Accessed 4 May 2001 at http://www.savebay.org/kidsweb/about_the_Bay/inside_mummichog.htm.