Lepisosteus oculatusSpotted gar

Last updated:

Geographic Range

The northern range of Lepisosteus oculatus stretches throughout the Lake Michigan and Lake Erie drainages. It is also found in the Mississippi River drainages, and river drainages along the northern coast of the Gulf of Mexico from the Nueces River in Texas east to the lower Apalachicola River in Florida. (Pope and Wilde, 2003; Schultz, 2004)

Habitat

Spotted gar prefer shallow open waters, usually 3 - 5 m deep, as well as stagnant backwater. They are often found near the surface basking near fallen logs, trees, or brush. This species is also shoreline-oriented, meaning it can be found near banks that include some sort of brush covering. Spotted gar are rarely found in areas that do not include some form of brush covering. (Snedden, et al., 1999)

  • Range depth
    3 to 5 m
    9.84 to 16.40 ft

Physical Description

This species of gar rarely exceeds 91 cm, and the average length is 76 cm. Its body is cylindrical and often mistaken for a log lying in shallow waters. This gar is covered with hard, diamond-shaped ganoid scales. Their bodies are spotted, including the top of the head and the fins. Lepisosteus oculatus is often mistaken for the Florida gar, Lepisosteus platrhynchus; the two can be distinguished by the distance from the eye to the gill cover. In the spotted gar, this distance is greater than two-thirds the snout length, while this distance in the Florida gar is less than two-thirds. Females are generally larger than males, probably due to their reproductive investment. One study reported the mean standard length of a male to be 432.2 mm and that of the female to be 486.2 mm. (Love, 2004; Schultz, 2004)

  • Sexual Dimorphism
  • female larger
  • Range mass
    1 to 4 kg
    2.20 to 8.81 lb
  • Range length
    100 to 914 mm
    3.94 to 35.98 in
  • Average length
    760 mm
    29.92 in

Development

Larval gars hatch from eggs, and are about 2.5 cm long when they first emerge. They are very slender and movement is assisted by a filament on the tail that vibrates. The filament does not last long, as gars grow larger at a fast rate. Spotted gar are fully developed by age 2. One study found that males grow significantly faster than females, but have a shorter lifespan. Love (2004) found that males (278 mm) and females (299 mm) grow at about the same rate in the first year of life. For the next 4 years, males grew faster than females: 48 mm/year vs 38 mm/year, respectively. Later in life, females (31 mm/year) outgrew males (16 mm/year). (Love, 2004; Love, 2004)

Reproduction

Multiple males gather in shallow (1.5 m) water near vegetation to compete for the larger females. Females allow more than one male to fertilize their eggs. Females splash and make quick movements at the moment the eggs are deposited. (Love, 2004)

Egg production is its highest in October, when females laid an average of 13,789 +/- 7654 (SE) eggs. Fecundity was lowest during June in which just 1,772 +/- 392 (SE) eggs were laid. Larger females lay more eggs. (Love, 2004; Tyler and Granger, 1984)

  • Breeding interval
    Females lay eggs once yearly.
  • Breeding season
    Spawning occurs from February to June, varying with location.
  • Range number of offspring
    1772 to 13789
  • Average time to hatching
    7 days
  • Average age at sexual or reproductive maturity (female)
    1 years
  • Average age at sexual or reproductive maturity (male)
    1 years

Females lay thousands of eggs during spawning, supplying nourishment in the eggs for the embryos. There is no parental care after the eggs are laid. Females lay thousands of eggs several months after spawning, supplying nourishment in the eggs for the embryos. There is no parental care after the eggs are laid. Females lay thousands of eggs several months after spawning, supplying nourishment in the eggs for the embryos. There is no parental care after the eggs are laid. Females lay thousands of eggs several months after spawning, supplying nourishment in the eggs for the embryos. There is no parental care after the eggs are laid. (Love, 2004; Love, 2004; Love, 2004; Love, 2004)

  • Parental Investment
  • pre-fertilization
    • provisioning
    • protecting
      • female

Lifespan/Longevity

Although maximum ages are not readily available, Love (2004) found gar populations in a Louisiana estuary to range from 0 - 8 years of age in males, and 0 - 10 years in females. (Love, 2004)

  • Average lifespan
    Status: captivity
    18 years
    AnAge

Behavior

The spotted gar is primarily nocturnal. Often, this species will remain stationary near fallen trees or brush throughout the day. They typically become more active at night and extend their home range in order to search for prey. Because their prey consists primarily of crayfish, logs and brush also serve as foraging cover. Occasionally, the gar will break the surface of the water to take air into their specialized physostomous swim bladder. This specialized bladder therefore acts as a primitive lung, and allows them to inhabit waters with oxygen concentrations < 2.0 mg/L. (Schultz, 2004; Snedden, et al., 1999)

  • Range territory size
    0.9 to 162.73 km^2
  • Average territory size
    2.65 km^2

Home Range

The home range (defended territory) of the spotted gar increases at night when the fish is foraging. Because this species prefers shallow waters, it will abandon its home range if the waters become too deep. This is often the case in the spring, when the home range (average 265.1 ha)is typically 20 times larger than in other seasons (median 6.6 ha). Spotted gar are known to abandon or extend their home range during the spawning season. However, during the fall, winter, and summer their home range does not vary greatly. The median movement rate of the spotted gar is 21.9 meters/hour. This rate rarely exceeds 60 m/h. These movements are typically not in the upstream or downstream direction, but instead they are movements across the floodplain. They move among backwater sloughs and seasonally flooded pools. (Snedden, et al., 1999)

Communication and Perception

Methods of communication among spotted gars aren't well-studied. They have a lateral line system that may help them sense prey in the turbid waters they live in.

Food Habits

This species of gar is an ambush predator, feeding primarily on aquatic crustaceans, such as crayfish (47% of diet in one study). They utilize their brush covered habitat for foraging at night. Spotted gar also eat other species of fish including sunfish, gizzard shad, crappies, bass, catfish, and shiners. One study showed that this species can feed efficiently across a spectrum of habitat complexity, and that some species were simply more vulnerable to gar attack regardless of cover. (Ostrand, et al., 2004; Snedden, et al., 1999)

  • Animal Foods
  • fish
  • insects
  • aquatic crustaceans

Predation

Adult spotted gars do not have many natural predators. Most of the predators that prey on spotted gars are other types of gars, such as the alligator gar (Atractosteus spatula). Eggs and juvenile spotted gars are probably attacked by a number of aquatic predators, although the eggs of gar are potentially toxic to many species. The spotted pattern on these fish may act as camouflage. (Pope and Wilde, 2003)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Spotted gars are important predators of crayfish, other crustaceans, and smaller fish in the low-oxygen level waters they inhabit.

Economic Importance for Humans: Positive

Juvenile spotted gar eat mosquito larvae. The species is not particular popular for sport fishing, although gars are considered good fish for eating.

  • Positive Impacts
  • food

Economic Importance for Humans: Negative

Spotted gars sometimes attack popular game fish species, but there is no evidence that they effect populations of game fish. Existing studies show they prey on mainly non-game species.

Conservation Status

Spotted gars are not generally considered in need of special conservation efforts, except at the edges of their range, where numbers have shrunk due to habitat destruction. They have not been evaluated by the IUCN. Spotted gar are Species of Special Concern in Michigan, Threatened in Canada (Ontario Province), and may have protected status in other states on the northern, eastern, and western limits of theirrange.

Other Comments

Until the early 1960s, this species was known as Lepisosteus oculatus. It is not considered a good "eating" fish, in part because it is difficult to clean, and its roe may be toxic to humans. (Schultz, 2004)

Contributors

George Hammond (editor), Animal Diversity Web.

Lana Hall (author), Radford University, Thomas Meade (author), Radford University, Drew Paulette (author), Radford University, Josh Albert (author), Radford University, Karen Powers (editor, instructor), Radford University.

Stephanie Givinsky (author), University of Michigan-Ann Arbor.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

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.

brackish water

areas with salty water, usually in coastal marshes and estuaries.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

external fertilization

fertilization takes place outside the female's body

fertilization

union of egg and spermatozoan

food

A substance that provides both nutrients and energy to a living thing.

freshwater

mainly lives in water that is not salty.

intertidal or littoral

the area of shoreline influenced mainly by the tides, between the highest and lowest reaches of the tide. An aquatic habitat.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

piscivore

an animal that mainly eats fish

poisonous

an animal which has a substance capable of killing, injuring, or impairing other animals through its chemical action (for example, the skin of poison dart frogs).

polyandrous

Referring to a mating system in which a female mates with several males during one breeding season (compare polygynous).

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

visual

uses sight to communicate

References

Hubbs, Carl L., and Lagler, Karl F. 1964. Fishes of the Great Lakes Region. University of Michigan Press.

Bowler, 1987. Recent observations of the distribution and status of the Freckled Madtom and the first record of Spotted Gar in Iowa. The Journal of the Iowa Academy Science, 3-4: 40-43.

Love, J. 2004. Age, growth, and reproduction of spotted gar Lepisosteus oculatus (Lepisosteidae) from the Lake Pontchartrain estuary, Louisiana. Southwestern Naturalist, 49/1: 18-23.

Ostrand, K., B. Braeutigam, D. Wahl. 2004. Consequences of vegetation density and prey species on Spotted Gar foraging. Transactions of the American Fisheries Society, 133/3: 794-800.

Pope, K., G. Wilde. 2003. Variation in spotted gar (Lepisosteus oculatus) mass-length relationships in Texas reservoirs. The Texas Journal of Science, 55.1: 43-49.

Schultz, K. 2004. Ken Schultz's Field Guide to Freshwater Fish. Hoboken, NJ: John Wiley & Sons, Inc. (US).

Snedden, G., W. Kelso, D. Rutherford. 1999. Diel and seasonal patterns of Spotted Gar movement and habitat use in the Lower Atchafalaya River Basin, Louisiana. Transactions of the American Fisheries Society, 128: 144-154.

Tyler, J., M. Granger. 1984. Notes on food habits, size, and spawning behavior of Spotted Gar in Lake Lawtonka, Oklahoma. Proceedings of the Oklahoma Academy of Science, Volume 64: 8.