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Bowfin (Amia calva)

Brent Courchene

 

Contained in the order Amiiformes are a number of extinct families, but one fish remains as the only living predecessor to endure the test of time. Of the six bowfin families that were prevalent in the Jurassic and Cretaceous periods (150 million years ago) the bowfin, belonging to the Amiidae family, is the only "true" bony fish that is left (Lee, 1980). The fish is literally a swimming fossil of ancient, highly predaceous marine organisms. The bowfin has a variety of alias’s depending on where they are found, people refer to them as grindle, blackfish, mudfish, dogfish, cypress trout, tourist trout, and choupique. The bowfin is a very good evolutionary indicator for the way things used to be, displaying the fossil past of most other prehistoric bony fishes.

Amia calva is an easily recognized fish, despite Amia in Greek meaning unidentified fish. The gar-like body is laterally elongated and cylindrical, with a single continuous dorsal fin made of 45 to 50 soft rays that runs from the middle of its back, and terminates where the tail begins. It has a prominent backbone that flexes upwards towards the caudal fin. The tail of this fish entails a single lobe, which gives the appearance of an almost circular shape. The fish’s anal fin is small and located close to the rear, its pelvic fins are close to the middle of its body, and its pectoral fins are small and rounded. Besides it’s head, the body is covered with cycloid scales, with 64-70 of them along the lateral line. The color of the Amia varies, but is usually olive colored with blotches of various shades of brown (Lee, 1980). The fins are typically olive-green, and its underside is a lighter cream color. Usually bowfin will have a dark black spot on the dorsal edge near the base of it’s tail, and males will have a dark spot on the tips of their caudal fins surrounded by a bright orange or yellow border (Grzmek, 1984). The fish displays a pointed head that narrows from top to bottom with a short rounded snout. The bowfin has a gular bone, a flat plate on the floor of the mouth between the lower jaws, that is not found in any other North American freshwater fishes, as well as two barbels that project anteriorly from its nose (Fauna, 1998). Bowfin have concave vertebrae which make it very streamlined, as well a mouth that is full of many small sharp teeth. The fishes mouth opening is broad, extending all the way to beneath the eyes, and is also perfectly horizontal. All these physical attributes have remained since prehistoric times, but as environments have changed the bowfin have shown that their form not need to, because it is so advantageous in the places they inhabit.

Bowfin live in a variety of habitats, and have inhabited a good portion of North America, but cease to exist anywhere else in the world. Amia’s distribution covers the majority of the Mississippi River basin, and extends east along the Gulf coast covering the entire peninsula of Florida, eventually extending north up the Atlantic Coast to the New Jersey section of the Delaware River (Frank, 1973). Amia has also found its way into the Great Lakes, Saint Lawrence River, and Lake Champlain through migratory routes that most of North American aquatic organisms use.

Amia prefer slow, sluggish, quiet backwaters that are dominated by aquatic macrophytes. The bowfin’s color provides it with good camouflage while it lingers along the margins of aquatic vegetation, in undercut banks, as well as branches and other submerged structures (Richmond, 1999). Ideally Amia is suited best in when temperatures are 18-25 degrees Celsius, and pH levels that are neutral to slightly acidic (pH 6.6-7.2) (Bootzy, 1999). As previously mentioned bowfin can survive in water with varying dissolved oxygen levels, which is prevalent most of time in the weedy beds where it lives. In this situation the bowfin will come right up to the surface and breath oxygen out of the air, by employing its primitive swim bladder. This swim bladder is equipped with blood vessels and can serve as a primitive lung (Fauna, 1998).

Many tests have been done in order to determine exactly what regulates the bowfin’s breathing patterns. In 1999, Hedrick found that bowfin evolved two air breathing mechanisms in a single organ that coped with the conflicting demands of buoyancy, and gas exchange. He discovered that gas exchange is regulated by exhalation followed by inhalation (type I breathing), whereas buoyancy is regulated by inhalation alone (type II breathing) which simply replaces the gas lost by diffusion across the respiratory surface. In 1993, Hedrick also found that bowfin’s breathing responds to internal intervascular oxygen levels, meaning type II breathing is controlled by volume sensitive stretch receptors in the gas bladder. It follows that at rest, bowfin’s will have modest oxygen consumption from the air, and at low level exercise air breathing will increase. Farmer 1999, discovered at low level exercise more than 50% of oxygen was attained through aerial breathing.

During the night bowfin are aggressive eaters, usually feasting on insects, leeches, crawfish, frogs, or even other fish, making the bowfin piscivorous (fish that eat fish). During the colder months the fishes become almost totally inactive, seeking deeper water where they can pack themselves in large groups while they rest for the winter. When the water in shallow areas becomes about 16 to 19 degrees Celsius the bowfins emerge in small groups, displaying brilliant coloration that has become vibrant over the winter (Grizmek, 1984). In the case of a drought, the bowfin will defend itself by burying its entire body in the thick bottom mud.

Between May and June bowfin’s spawn in the thick weed beds of shallow waters (Frank, 1973). It takes about 3 males for every female that seeks spawning grounds; it is also the males that do most of the work when it comes time to breed. Males first build a circular nest in the weeds, that is 10 to 20 cm deep, with a diameter of 30 to 90 cm (Grzmek, 1984). This nest is not your typical breeding grounds like that of a sunfish or bass. Instead of clearing a depression in the sand, the bowfin males build nests in fibrous root mats by clearing away the stems and leaves of aquatic plants. Before spawning the male and female engage in a special courtship dance. After spawning is completed the male guards the fertilized eggs (up to 64,00 eggs at a time) until they hatch, usually 8 to 10 days later (Bootzy, 1999). The colorless larvae (7 mm long) attach themselves to aquatic plants using the tips of their snouts as an adhering disc (Frank, 1973). The male Amia continues to protect his offspring against predation, while the young fry now hover close together in one big school over the nest. Juvenile bowfin have beautiful orange, black, and green fin and gill plates, and will continue to swim in schools until they reach about 4 inches long (Richmond, 1999).

Bowfin has become increasingly important in recent years in the sport fishing industry. Amia are sought after by fisherman because of the size of the fish, as well as the excellent fight they exhibit once they are hooked. Bowfin can live as long as 30 years, some have been recorded that are 3 feet long, and weigh as much as 15 pounds. These fish are also very important in the wild because they are such voracious eaters. Bowfin’s have a very diverse diet, which means they don’t depend on one single food source. Instead Amia feed on whatever is abundant; keeping control of fish and other organism’s populations that may be getting overabundant. Amia calva are also commonly used as a test animal because of their status as a living fossil, ease of maintenance, and interesting behavioral and physiological attributes.

Literature Cited

Bootzy, A. L., 1999. Jurrassic Carnivore. http://www.aquariacentral.com/fishinfo/cold /bowfin.shtml

Farmer, C. G., D. C. Jackson, 1998. Air Breathing During Activity in the Fishes Amia calva and Lepisosteus. Journal of Experimental Biology. 201(7):943-948

Fauna of Okefenokee Swamp, 1998. http://www.gwf.org/okefauna.htm

Frank, S., 1973. The Pictorial Encyclopedia of Fishes. Pages 41-43

Grzmek, B., 1984. Animal Encyclopedia (Fishes I). 4:149-152

Hendrick, M. S., D. R. Jones, 1993. Effects of Altered Aquatic and Aerial Respiratory Gas Concentrations on Air Breathing Patterns in a Primitive Fish. Journal of Experimental Biology. 181(1):81-94

Hendrick, M. S., D. R. Jones, 1999. Control of Gill Ventilation and Air Breathing in the Bowfin. Journal of Experimental Biology. 202:87-94

Lee, D. S., 1980. Atlas of North American Freshwater Fishes. 53-54

Richmond, A., 1999. Bowfin. http://www.bio.umass.edu/biology/conn.river/bowfin.html