Each family of fishes in the Great Lakes region has physical traits that set it apart from others, called distinguishing characteristics. These characteristics help fish survive in their environment. By observing and comparing these features, students learn that fish, like other living organisms, can be organized and classified into meaningful groups for identification and further study.
Grade level: 4-8th grades
- MS-LS4.4 Biological Evolution: Unity and Diversity. Construct an explanation based on evidence that describes how genetic variations of traits in a population increase some individuals’ probability of surviving and reproducing in a specific environment.
- MS-LS4.6 Biological Evolution: Unity and Diversity. Use mathematical representations to support explanations of how natural selection may lead to increases and decreases of specific traits in populations over time.
For alignment, see: NGSS Summary
- Describe the physical characteristics (traits) of fish that help them survive in their environment.
- Name several distinguishing characteristics of Great Lakes fish.
- Describe how these characteristics help fish survive in their environment.
- Organize Great Lakes fish (cards) based on similarities and differences.
- Use a dichotomous key to identify 10 Great Lakes fish families.
The Great Lakes region is home to an impressive variety of fish, numbering more than 160 separate species. It is helpful to understand:
- A species consists of individuals that share the same gene pool.
- These species belong to 28 major fish families.
- A family is a taxonomic group that includes similar species.
Many in the Great Lakes are familiar with fish in the sunfish and bass family, cold-water species in the salmon and trout family, or some of the 62 species that make up the minnow family.
Ancient fish such as lake sturgeon and longnose gar also inhabit waters of the Great Lakes region and possess unique attributes that have allowed them to survive for millions of years. With the exception of some primitive species, most fish have common characteristics that include gills, scales, fins and bony skeletons. Some characteristics that differentiate fish include the shape of their heads, where their mouths are located, fin type and location, and average adult size.
Color markings, such as vertical stripes or fin spots, may also help differentiate fish when used in combination with other factors including geographic range. Distinguishing characteristics can provide clues about where a species typically lives and what it eats.
For example, fish in the sturgeon and sucker families have downward-oriented mouths (sometimes called ventral) that enable them to find food along a lake or stream bottom. Other traits such as fin shape and location can provide clues about whether a fish is generally a fast swimmer or a slow swimmer.
To correctly identify fish and classify newly discovered species, fisheries scientists use a dichotomous key based on distinguishing characteristics. A dichotomous key is a classification tool used to sort, organize and identify a collection of objects or living organisms. The key is made up of a series of questions with two choices. Each choice leads to another question. The key can appear in narrative form (as numbered questions), graphically (resembling a flow chart), or a combination of graphics and narrative.
By making choices and progressing logically through the key, users follow a path that ends with the correct identification of the organism. Dichotomous keys vary in their degree of specificity. In this lesson, a simplified key has been created that distinguishes 10 Great Lakes fish families. By using their knowledge of distinguishing characteristics, students use illustrations of fish to work through the key and make identifications.
Assessment & Standards
See separate document: Lesson Assessment, State of Michigan Content Expectations and National Benchmarks (PDF)
- Can I See Some ID Please? How to Identify Fish
Summary: Working with a set of Great Lakes fish cards, students identify distinguishing characteristics of fish and use a dichotomous key to identify 10 common fish families.
Time: 30-60 minutes
Lepisosteus osseus is widely distributed throughout the eastern United States. L. osseus can be found along the eastern seaboard from the Delaware River, N.J. to central Florida and in the upper Midwest in the St. Lawrence River, Quebec and all of the Great Lakes except Superior. It lives throughout the entire Mississippi River basin and can be found as far south as the Rio Grande drainages of Texas and Mexico (Page and Burr, 1991).
L. osseus live in a variety of lowland habitats, preferring sluggish areas of larger rivers, lakes, reservoirs and estuaries. They can live in brackish water and are common in the deeper bayous along the Gulf Coast (Goodyear, 1967). L. osseus can tolerate high water temperatures and can often be found near the water surface on warm days or nights (Becker, 1983).
- lakes and ponds
- rivers and streams
Longnose gar have long, narrow snouts more than twice as long as the rest of the head and they have abundant, sharp, villiform teeth. Mature L. osseus are olive brown in color with a white belly. Dark spots can be found on the median fins and, in individuals from clear water, on the body. Young L. osseus have a narrow brown stripe along their back and a broad dark brown strip along their sides (Page and Burr, 1991; Becker, 1983). The dorsal and anal fins of the longnose gar are located far back on the body, which is encased in a heavy armor of interlocking, rhomboid, ganoid scales (Ross, 2001).
L. osseus eggs typically hatch 3-9 days after they have been laid and the larvae are approximately 8-10 mm long at hatching (Yeager and Bryant, 1983; Becker, 1983). The yolk sac is absorbed at approximately 12 mm TL and fins form around 30 mm TL (Simon and Wallus, 1989). Early-stage L. osseus larvae (sac-fry) are relatively inactive and possess an adhesive structure at the tip of the snout by which they attach to objects in the water. By 10 to 11 days after hatching, L. osseus are 18-20 mm long. Young longnose gar grow rapidly and studies have shown that they can gain 3.2 mm and 1.8 grams per day, when maintained in aquaria with an unlimited food supply (Riggs and Moore, 1960). Male longnose gar will typically mature at three to four years of age while females do not mature until six years (Ross, 2001).
During the mating process as many as 15 males may approach the female. If she is ready, she will lead them in an elliptical pattern for up to 15 minutes prior to spawning. Once over the spawning bed, the males will nudge the female with the ends of their snouts in the pectoral, lateral, and ventro-lateral areas. During this phase, frequent surfacing and gulping take place. Ultimately, the spawning group will position itself at one place with heads down and snouts very close to the bottom. Rapid and violent quivering follows as the sperm and eggs are released (Haase, 1969).
Spawning occurs in the spring and summer for L. osseus. In rivers, longnose gar make upstream spawning runs during the spring period of high water, then move downstream into larger pools. They have also been seen spawning in open, wind-exposed areas over rocks as well as gravelly, weedy sites. Spawning takes place in shallow water resulting in the backs of the fish sometimes being exposed. Often, more than one male will attend to the larger female during spawning. She will not release all of her eggs at the same time. Once shed, the eggs become very sticky and adhere to solid objects on the substrate (Ross, 2001). Females produce about 30,000 eggs per year; 77,000 eggs were once recorded in a female observed in Tennessee (Etnier and Starnes, 1993).
L. osseus provide no parental care. Research has shown frequent occurrences of the longnose gar laying eggs in smallmouth bass nests, where the male bass guarding the nest provides protection for the young gar in addition to its own young (Goff, 1984).
Longnose gar can be aged by annular marks on their branchiostegal rays. Female L. osseus grow more quickly and live longer than males. They are capable of living well beyond 17 years and some have reached 22 years in the wild. In captivity, female L. osseus have lived up to 30 years (Ross, 2001). Male longnose gar typically do not live longer than 11 years in the wild. A study by Netsch and Witt (1962) in Missouri did not find any males older than 17 years of age.
A unique behavior of the longnose gar is its ability to survive in low-oxygen waters. L. osseus has a highly vascularized swimbladder, which connects to the pharynx by a pneumatic duct, to breath air. Under normal oxygen levels, both aquatic and aerial respiration occurs. However, as oxygen becomes limited, L. osseus will close its gill covers and can survive indefinitely on aerial respiration alone (McCormack, 1967).
Communication and Perception
The communication of L. osseus is not well understood. They are a gregarious fish though, often found in groups of two to five, sometimes along with shortnose gar (Lepisosteus platyrhincus) (Holloway, 1954).
By 10-11 days after hatching, young gar begin feeding on small crustaceans, such as cladocerans and copepods, and insects, including various dipterans such as chironomids. L. osseus quickly switch to a diet of primarily fish. Gars are active night feeders and much of the feeding is surface-oriented (Becker, 1983). They catch their prey sideways in their well-toothed jaws by lying motionless or slowly stalking prey until the smaller fish are within reach. L. osseus slashes its beak from side to side, impaling the prey on its teeth. The prey is then maneuvered into position to be swallowed headfirst (Branson, 1966).
In most studies of adult L. osseus, a variety of species made up a majority of the diet, with the dominant prey changing among locations. Inland silversides were particularly common prey of juvenile gar in Lake Texoma, making up 84% of the diet, with gamefishes accounting for less than 1% of the diet (Eschelle, 1968). In Florida, the diet was comprised mainly of fishes, with gizzard shad, bullhead catfish, and small bluegill particularly common (Crumpton, 1971). In Missouri, Netsch (1964) found that fishes made up 98% of the diet with shiners being the most common prey. In some lakes, adult longnose gar may consume large numbers of sunfishes. Menhaden are a major food source along coasts where L. osseus move towards the mouth of bayous into higher salinity waters in the afternoon and evening to find this more prevalent prey. Longnose gar will then move back up the bayous, into the lower salinity waters in the morning (Ross, 2001).
As previously mentioned, L. osseus are encased in a heavy armor of interlocking, rhomboid, ganoid scales. The ganoid scales are composed of two layers, an outer layer of ganoin and an inner layer of isopedine, both of which are penetrated by blood vessels. As a result of this armor, the longnose gar has no major predators. There have been occurrences of longnose gars being attacked by alligators, but research suggests that these may have been opportunistic events (McCormack, 1967).
The general perception of L. osseus is that it is a nuisance or “trash” fish. However, all species of gar serve as hosts to the parasitic young (glochidia) of the yellow sandshell, a freshwater mussel. Without gar, this mussel would disappear unless it was maintained by artificial means (Becker, 1983).
Economic Importance for Humans: Positive
L. osseus, although palatable, are not particularly popular or sought after by anglers. There is a commercial fishery for longnose gar in Arkansas though (Ross, 2001). Consideration has been given to gars as a possible aid in controlling overpopulation of sunfish and yellow perch as well (Niemuth et al., 1959). Additionally, gar skins have been used to a small extent for covering picture frames, purses, and the like. The gar scales are very hard and take on a fine polish (Forbes & Richardson, 1920).
Economic Importance for Humans: Negative
L. osseus have historically been perceived as detrimental to game species, such that gar management has emphasized removing the species from aquatic environments (Johnson and Nolte, 1997). In addition, the longnose gar has a propensity for becoming entangled in nets and is considered a pest by commercial fisherman (Ross, 2001). Forbes and Richardson (1920) stated: “it is a wholly worthless and destructive nuisance in relation to mankind. It has, in fact, all the vices and none of the virtues of a predaceous fish” (Netsch and Witt, 1962).
L. osseus is not listed on the IUCN list, the United States Endangered Species Act list or the CITES appendices.
The large, greenish eggs of L. osseus are toxic to humans, other mammals and birds and should not be eaten (Netsch and Witt, 1962). Historically, the heavy rhomboid scales of the gar were often used by local Indians for arrow points, ornaments, and other instruments (Suttkus, 1963).
William Fink (editor), University of Michigan-Ann Arbor.
Bruce Rudy (author), University of Michigan-Ann Arbor.
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.
- 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.
an animal that mainly eats meat
uses smells or other chemicals to communicate
the nearshore aquatic habitats near a coast, or shoreline.
an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.
- external fertilization
fertilization takes place outside the female's body
union of egg and spermatozoan
A substance that provides both nutrients and energy to a living thing.
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.
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).
makes seasonal movements between breeding and wintering grounds
having the capacity to move from one place to another.
specialized for swimming
- native range
the area in which the animal is naturally found, the region in which it is endemic.
active during the night
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
- pet trade
the business of buying and selling animals for people to keep in their homes as pets.
an animal that mainly eats fish
Referring to a mating system in which a female mates with several males during one breeding season (compare polygynous).
- saltwater or marine
mainly lives in oceans, seas, or other bodies of salt water.
- seasonal breeding
breeding is confined to a particular season
remains in the same area
reproduction that includes combining the genetic contribution of two individuals, a male and a female
associates with others of its species; forms social groups.
uses touch to communicate
Becker, G. 1983. Fishes of Wisconsin. Madison: University of Wisconsin Press.
Branson, B. 1966. The gar, a plea for a heritage of past. Kentucky Happy Hunting Ground,, 22 (July): 16-19.
Crumpton, J. 1971. Food habits of longnose gar (*Lepisosteus osseus*) and Florida gar (*Lepisosteus plaryhincus*) collected from five central Florida lakes. Proceedings of the Annual Conference of the Southeastern Association of Game and Fish Commissioners,, 24 (1970): 419-424.
Eschelle, A. 1968. Food habits of young-of-year longnose gar in Lake Texoma, Oklahoma. The Southwestern Naturalist,, 13: 45-50.
Etnier, D., W. Starnes. 1993. The Fishes of Tennessee. Knoxville: The University of Tennessee Press.
Forbes, S., R. Richardson. 1920. The Fishes of Illinois. Urbana: Illinois Natural History Survey.
Goff, G. 1984. Brood care of the longnose gar (*Lepisosteus osseus*) by smallmouth bass (*Micropterus dolomieui*). Copeia,, 1984: 149-152.
Goodyear, C. 1967. Feeding habits of three species of gars, *Lepisosteus*, along the Mississippi Gulf Coast. Transactions of the American Fisheries Society,, 96: 296-300.
Haase, B. 1969. An ecological life history of the longnose gar, *Lepisosteus osseus* (Linnaeus), in Lake Mendota and several other lakes of southern Wisconsin. Madison: Doctoral dissertation. University of Wisconsin.
Holloway, A. 1954. Notes on the life history and management of the shortnose and longnose gars in Florida waters. Journal of Wildlife Management,, 18(4): 438-449.
Johnson, B., D. Noltie. 1997. Demography, growth, and reproductive allocation in stream-spawning longnose gar. Transactions of the American Fisheries Society,, 1216: 438-466.
McCormack, B. 1967. Aerial respiration in the Florida spotted gar. Quarterly Journal of the Florida Academy of Science,, 30(1): 68-72.
Netsch, N. 1964. Foods and feeding habits of longnose gar in central Missouri. Proceedings of the Annual Conference of the Southeastern Association of Game and Fish Commissioners,, 18: 506-511.
Netsch, N., A. Witt Jr. 1962. Contributions to the life history of the longnose gar (*Lepisosteus osseus*) in Missouri. Transactions of the American Fisheries Society,, 91(3): 251-262.
Niemuth, W., W. Helm, V. Hacker. 1959. Life history, ecology and management of the longnose gar. Madison, Wisconsin: Report to the Conservation Division, Wisconsin Department of Natural Resources.
Page, L., B. Burr. 1991. Peterson Field Guide to Freshwater Fishes. Boston: Houghton Mifflin Company.
Riggs, C., G. Moore. 1960. Growth of young gar (*Lepisosteus*) in aquaria. Proceedings of the Oklahoma Academy of Science,, 40: 44-46.
Ross, S. 2001. The Inland Fishes of Mississippi. Jackson: University Press of Mississippi.
Simon, T., R. Wallus. 1989. Contributions to the early life histories of gar (*Actinopterygii: Lepisosteidae*) in the Ohio and Tennessee river basins with emphasis on larval development. Transactions of the Kentucky Academy of Science,, 50: 59-74.
Suttkus, R. 1963. Order Lepisostei. Sears Foundation for Marine Research,: 61-88.
Yeager, B., R. Bryant. 1983. Larvae of the longnose gar, *Lepisosteus osseus*, from the Little River in Tennessee. Journal of the Tennessee Academy of Science,, 58: 20-22.