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Bowfin

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The ruddy bowfin (*Amia calva*) is a remarkable ray-finned fish native to North America.

Usfws-bowfin-ryan-hagertyjpg
Usfws-bowfin-ryan-hagertyjpg

Scientists often call this species a "living fossil." This term describes how the bowfin has kept many physical traits from its ancient ancestors. The bowfin belongs to a group called Halecomorphi. This group first appeared during the Early Triassic period, about 250 million years ago. Today, the bowfin is one of only two surviving species in that entire group. Its closest living relatives are gars. Both bowfins and gars belong to a larger group known as Holostei.

Cladogram of basal actinopterygians and neopterygians
Cladogram of basal actinopterygians and neopterygians

Bowfins are demersal freshwater piscivores, which means they live near the bottom and eat other fish. They are primarily found in the eastern United States and southern Canada. Their range includes the drainage basins of the Mississippi River and the Great Lakes. They also live in rivers that flow into the Gulf of Mexico or the Eastern Seaboard. These fish prefer habitats like vegetated sloughs, swamps, and lowland lakes. They can also be found in brackish water, which is slightly salty.

USGSmapBowfinDist
USGSmapBowfinDist

One of the most incredible things about the bowfin is how it breathes. Most fish rely entirely on gills to extract oxygen from the water. However, the bowfin is a bimodal breather. This means it can breathe both water and air. The fish possesses a gas bladder to help it stay buoyant in the water. A small tube called a pneumatic duct connects the foregut to this gas bladder.

Amia Gas Bladder
Amia Gas Bladder

By breaking the water's surface, the bowfin can gulp air through this duct. This ability allows them to survive aquatic hypoxia. Hypoxia is a condition where there is very little oxygen in the water. This would be lethal to many other fish species.

As ambush predators, bowfins use specific hunting strategies to survive. They are stalking hunters that often move into shallow waters at night. They prey on fish and various aquatic invertebrates. This includes creatures like crawfish, mollusks, and aquatic insects. Their mouth is specially designed for this diet. They have two distinct sets of teeth. The first set consists of large, sharp teeth on the jaw bones to grasp prey. The second set is located further back in the throat. These are called pharyngeal tooth patches. They are attached to the hyomandibular bone and help grind food.

Dorsal View of a Bowfin skull
Dorsal View of a Bowfin skull

The physical structure of the bowfin is quite complex. The body is long and cylindrical, with colors ranging from olive to brown. They often have vertical bars or dark patterns for camouflage. A very long dorsal fin runs from the middle of the back to the tail. This fin contains between 145 and 250 rays. The skull is composed of two layers: the chondrocranium and the dermatocranium. The dermatocranium is the outer layer made of 28 fused bones.

AmiaCalvaHeadLankester
AmiaCalvaHeadLankester

Underneath the head, they also have a bony gular plate.

Young males often have a black eyespot on the base of their tail. This eyespot may confuse predators by making them strike the tail instead of the head.

Evolution has shaped the bowfin into a highly capable swimmer. Their vertebral column is ossified, meaning it is made of bone. In earlier fish, a structure called a notochord provided most of the support. In the bowfin, the bony centra provide the main support. This change allows the fish to handle the pressure of bending its body. It also allows for more powerful and controlled movements. Their tail is a rounded heterocercal fin. This shape helps create a streamlined body that reduces drag.

Hal - Cyprinus carpio and Amia calva skeletons
Hal - Cyprinus carpio and Amia calva skeletons

It is important to distinguish the bowfin from similar-looking fish. The northern snakehead is often mistaken for a bowfin. However, the snakehead is an invasive species from Asia and Russia. Unlike the bowfin, the snakehead has scales that cover its head. You can also tell them apart by their head shape and fin placement. Another similar fish is the burbot. Burbots can be identified by their flat heads and chin barbels. While they may look similar, the bowfin is a unique North American native. They are long-lived animals that can reach ages of up to 33 years.

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🖼️ Images & Media (11)
File:Usfws-bowfin-ryan-hagertyjpg.jpg
Usfws-bowfin-ryan-hagertyjpg.jpg
File:Dorsal View of a Bowfin skull.png
Dorsal View of a Bowfin skull.png
File:AmiaCalvaHeadLankester.jpg
AmiaCalvaHeadLankester.jpg
File:FMIB 47066 Amia calva; g, gular plate.jpeg
FMIB 47066 Amia calva; g, gular plate.jpeg
File:Bowfin.png
Bowfin.png
File:Hal - Cyprinus carpio and Amia calva skeletons.jpg
Hal - Cyprinus carpio and Amia calva skeletons.jpg
File:Amia Gas Bladder.jpg
Amia Gas Bladder.jpg
File:Cladogram of basal actinopterygians and neopterygians.png
Cladogram of basal actinopterygians and...
File:Gill Rakers of Amia Calva.jpg
Gill Rakers of Amia Calva.jpg
File:USGSmapBowfinDist.png
USGSmapBowfinDist.png
File:Lernaea parasite on a Murray cod.jpg
Lernaea parasite on a Murray cod.jpg
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