Bowfin
The bowfin (Amia calva) is a primitive bony fish in the genus Amia that lives in North America. It is a relict species, last of a group known as the Halecomorphi. That group appeared the Lower Triassic, about 250 million years ago.
The bowfin is described as "primitive" because they have characteristics of their early ancestors. The closest living relatives of bowfins are gars: the two groups make up the clade Holostei.
Their physiology is quite interesting. Like gars, bowfin are bimodal breathers: they can to breathe both water and air. Their gills exchange gases in the water, and they also have a gas bladder. The gas bladder is the secret: it keeps buoyancy, and lets the fish breathe air by a small pneumatic duct which goes from the foregut to the gas bladder. They break the surface to gulp air. This lets them survive conditions of hypoxia which would be lethal to most species.[1]
Bowfin body-shape evolution and development
The first fish lacked jaws and used negative pressure to suck their food in through their mouths. The jaw in the bowfin is a result of their evolutionary need to be able to catch and eat bigger and more nutritious prey. As a result of being able to gather more nutrients, Bowfin are able to live a more active lifestyle. The jaw of a bowfin has several adaptations.
Similar species
Some people mistake northern snakeheads (Channa argus) for bowfin because even if they are in a different genus, they have similarities to them in appearance, most noticeably their elongated, cylindrical shape, and long dorsal fin that runs along their backs.
Diseases
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A common parasite of bowfin is the anchor worm from the genus Lernaea. These crustaceans infest the skin and bases of fins, with consequences ranging from slowed growth to death.
Feeding
Bowfin are stalking, ambush predators that move into the shallows at night to prey on fish, and aquatic invertebrates such as crawfish, mollusks, and aquatic insects.
Bowfin Media
Bowfin activity in an aquarium 
Diagram showing fins and eyespot of a bowfin, USF&WS
Dorsal view of a bowfin skull, showing the pharyngeal tooth patches which are connected to the internal portion of the hyomandibular bone. Acquired from Pacific Lutheran University.
Drawing of a bowfin skull showing the bony plates protecting the head
Lateral view of a bowfin skull: The dermal bones that are seen are composed of dermatocranium and cover the chondrocranium which is present but is located underneath the layer of dermatocranium. This specimen came from the Pacific Lutheran University Natural History collection.
The lower figure is a skeleton of the bowfin. The pelvic and pectoral girdles are both visible and the axial and cranial elements are also both present.
Dissection of a bowfin swim bladder
Three divisions of Neopterygii comprising Lepisosteiformes, Amiiformes, and Teleostei
The gill rakers are short with blunt processes and with a small space in between them. They are connected to the gill arch of the gills.
Amia calva distribution in the eastern U.S., as well as from the St. Lawrence River and Lake Champlain drainage of southern Ontario and Quebec, westward around Great Lakes in southern Ontario into Minnesota
References
- ↑ Melvin L. Warren Jr.; Brooks M. Burr (July 2014). Freshwater Fish of North America. Volume 1: Petromyzontidae to Catostomidae. JHU Press. pp. 288–289. ISBN 9781421412016.