Lepisosteus oculatus

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.

• Biogeographic Regions
• nearctic nearctic
  • native native

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.

• Habitat Regions
• temperate temperate
• freshwater freshwater

• Aquatic Biomes
• lakes and ponds
• rivers and streams
• brackish water brackish water

• Wetlands
• swamp swamp

• Other Habitat Features
• intertidal or littoral intertidal or littoral

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.

• Other Physical Features
• ectothermic ectothermic
• bilateral symmetry bilateral symmetry
• poisonous poisonous

• Sexual Dimorphism
• female larger

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).

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.

• Mating System
• polyandrous polyandrous

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.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
  • external external
• oviparous oviparous

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.

• 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.

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.

• Key Behaviors
• natatorial natatorial
• nocturnal nocturnal
• motile motile
• sedentary sedentary
• solitary solitary
• territorial territorial

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.

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.

• Perception Channels
• visual visual
• tactile tactile
• chemical chemical

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.

• Primary Diet
• carnivore carnivore
  • piscivore piscivore
  • eats non-insect arthropods

• 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.

• Anti-predator Adaptations
• cryptic 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 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 productus . It is not considered a good "eating" fish, in part because it is difficult to clean, and its roe may be toxic to humans.

Additional Links

Encyclopedia of Life

BioKIDS Critter Catalog

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.

References

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.

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