Fishes of Canada's National Capital Region
Species Accounts
Amiidae - Bowfins - Poissons-castors
The Bowfin is found in freshwaters of eastern North America and is the only member of its family. Fossil amiids are known world-wide and the oldest are of Jurassic age, 135-195 million years ago. Eocene amiids have been described from British Columbia, Palaeocene and Cretaceous ones from Alberta and Palaeocene and Oligocene ones from Saskatchewan. The genus Amia has been extant for 70 million years; evolutionary change is very slow.
The general body form of a Bowfin is unmistakable. In addition there is a large bony structure on the underside of the head between the lower jaws known as a gular plate. Branchiostegal rays number 10-13. There are no pyloric caeca. The caudal fin is an abbreviate heterocercal one. Heterocercal tails have the vertebral column turned upwards into the upper lobe of the fin, which is longer than the lower lobe. In the Bowfin, the lobes are not noticeably different in size. Scales are cycloid but are reinforced with ganoin. Some teeth are pointed canines while others are peg-like. Gill rakers are reduced to knobs but bear small spines.
The Bowfin's relationships to other fishes have long been discussed and large monographs have been written on the details of its anatomy. It is, in a sense, a living fossil, since many related families and species were widespread in the Jurassic and Cretaceous periods, but the Bowfin is the only surviving representative. Unlike sturgeons, the skeleton is bony but it has the heterocercal tail and a trace of a spiral valve. The gular plate, heavy bone plates on the head, and ganoin containing scales are also ancient characters. It is now considered to be related to the Teleostei and, with its fossil relatives, is equal in rank to the thousands of teleost species. The Bowfin swimbladder can be used as a lung since it has an opening to the gut and the internal surface is well-supplied with blood vessels. This fish can survive out of water for a day, and thrives in low oxygen waters such as stagnant swamps. Recent studies have shown that Bowfins cannot aestivate like the tropical lungfishes because they cannot detoxify ammonia waste or reduce metabolism and they die after 3-5 days of air exposure.
Bowfin / Poisson-castor
Amia calva Linnaeus, 1766
Taxonomy
Other common names include Dogfish, Mudfish, Mud Pike, Grindle, Grinnell, Griddle, Spot-tail, Lawyer, Cottonfish, Blackfish, Speckled Cat, Scaled Ling, Beaverfish, Cypress Trout, Amie, Poisson de marais and Choupique. Bowfin refers to the long, undulating dorsal fin.
Key Characters
The gular plate, a large bony structure between the lower jaws on the underside of the head, identifies this freshwater fish.
Description
The dorsal fin has 42-58 soft rays, the anal fin 9-12 rays and the pectoral fin 16-18 rays. There are 62-70 scales in a complete lateral line. The anterior nostrils have barbel-like flap.
Colour
The back is a dark-olive or brownish with the flanks mottled, marbled or reticulated with olive and yellow. The belly varies from white to light green. The dorsal fin is dark olive with 2 dark broken stripes, the anal, pelvic and pectoral fins are bright green. Males have an eye spot at the upper caudal fin base. The spot is dark and about twice as large as the eye and is surrounded by an orange or yellow halo. This spot is absent in females. Such eyespots are used to deflect the attack of predators from the eye to the less important tail, which may well give the predator a slap in the face! The anal, pectoral and pelvic fins have orange bases and tips in males. Young fish are lighter overall and have a black margin to the dorsal and caudal fins. There is a narrow stripe from the snout through the eye onto the opercle. Young smaller than 3-4 cm are black.
Size
Attains 109 cm. The world, all-tackle record from Florence, South Carolina in 1980 weighed 9.75 kg and a 6.7 kg fish was taken from Whitefish Lake, Ontario.
Distribution
Found from the St. Lawrence and Lake Champlain drainage of southern Québec westward around the Great Lakes in southern Ontario as far as Minnesota. In the south it reaches Florida and Texas. There are no specimens in a museum collection definitively from the NCR. Halkett (1906) mentioned two specimens from the Ottawa River in the Fisheries Museum, Ottawa and Prince et al. (1906) also reported two specimens in the Museum from the Ottawa River (presumably the same two fish) but did note they may not have been caught near "the district". Bergeron and Brousseau (1982) and Bernatchez and Giroux (2000) map this species within the NCR but may have based this on Prince et al. (1906). However competent fishermen familiar with a wide variety of fishes have reported it from Britannia in the late 1940s, Rockland; and even below the Parliament Buildings, all in the Ottawa River (J. McLoughlin, personal communication, 1986; D. Brunton, in letter, 1987; E. Hendrycks, personal communication, 2000). Chabot and Caron (1996) map a specimen from the Ottawa River, near the mouth of the Gatineau River.
Origin
This species entered the NCR from a Mississippian refugium (Mandrak and Crossman, 1992).
Habitat
Bowfins prefer warm quieter waters with a lot of vegetation in lakes and river backwaters. They can survive temperatures up to 35°C in stagnant waters which other predatory fish cannot utilise. However they can be found too in clear water bodies that are quite cool. Bowfins gulp air at the surface even in well-oxygenated water. Their preferred temperature is 30.5°C. Bowfins can aestivate for short periods in a moist chamber, 20 cm in diameter and 10 cm below the soil surface when flood waters recede.
Age and Growth
Life span may exceed 30 years. Males are smaller than females and probably do not live as long. Bowfins become sexually mature at 3-5 years of age when they are about 61 cm (females) and 45.7 cm (males). Growth is rapid with some fish exceeding 20 cm in the first year of life.
Food
Food is mainly other fishes, with some crayfishes, aquatic insects and frogs, taken at night after moving into shallower water. The Bowfin feeds by a rapid lunge, opening the mouth to suck in the prey. The opening and closing of the mouth takes about 0.075 seconds. They can also move very stealthily by undulating the dorsal fin, moving both backwards and forwards.
Reproduction
This species spawns from April to June depending on latitude. Nests are constructed by the male in shallow (usually less than 1.5 m), weedy areas of lakes and rivers. The nests are under logs or other objects, or are circular areas up to 76 cm across where all vegetation has been bitten off and removed. The male defends his nest against other males and during the spawning season torn fins are not unusual as nests may be quite close together. Spawning takes place at 16-19°C when the male entices a female into the nest, circles her for 10-15 minutes while she lies on the bottom of the nest, and nips her snout and flanks. The male then lies with the female, their fins vibrate rapidly and eggs and sperm are released within a minute. This may happen 4-5 times over 1-2 hours. Several females may spawn with one male and each female may deposit eggs in more than one nest. Eggs number up to 64,000 in females but number up to 5000 in nests. They stick to the plant roots or gravel in the bottom of the nest. The male guards the eggs and fans them with his pectoral fins. Eggs are 2.8 x 2.2 mm in dimensions. The eggs hatch in 8-10 days and the young use an adhesive snout organ to attach to vegetation for a further 7-9 days while the yolk-sac is absorbed. The male continues to guard and herd the young fry until they are about 10 cm long. The fry form into a ball which follows the male. So defensive are males, that one attempted to attack a human standing on the bank, coming 20 cm or so out of the water and repeating the attack several times.
Importance
The Bowfin is a good sport fish on light tackle, but is seldom fished for and is very rare in the NCR. Some are taken elsewhere by spearing while diving. It is edible, though not particularly tasty, and some commercial catches in Ontario have been sent to the United States where it is a more familiar food fish and better appreciated. "Cajun caviar" is made out of the roe in Louisiana. Small Bowfins are excellent aquarium fish because of their "lung", colouration and predatory habits.
© Brian W. Coad (www.briancoad.com)