Home >> Science & Nature >> Animals & Science

What Type of Caudal Fin Does the Dogfish Shark Have?

Dogfish are a group of small sharks known as squaliform sharks. They range in size from the dwarf lanternshark, which is the smallest known shark, to the more than 20 foot long Greenland shark. Dogfish are also the sharks found at the greatest depth, about 2,950 feet below the ocean's surface. As with all sharks, dogfish have distinctive caudal or tail fins, which reveal much about how they live.

Shark Fins in General
- Unlike sharks, the fins of bony fish like this lionfish are made of tiny bony spines.
  
  One of the distinguishing characteristics of sharks is that their skeleton is soft, flexible cartilage instead of bone. Their fins are more fleshy and solid than those of bony fish and do not have bony rays. Their fins are used mostly for movement, either generating forward movement or stabilizing movement. Dogfish have poisonous spines in front of their dorsal and adipose fins, the first and second back fins, respectively.
Fin Shape
- Though not dogfish, this nurse shark has a very similar curved, heteroceral caudal fin.
  
  All of a fish's fins are adapted to that particular fish's way of life. The tail fin of the dogfish is no different. The shape of a dogfish's tail is called a heterocercal caudal fin. In this fin shape, the top lobe is larger than the bottom, and both lobes are pointed. On some dogfish, the top lobe is sloped gradually, almost in line with the rest of the body.
Movement
- Like the dogfish, this black-tipped reef shark uses a heterocercal tail to cruise in the ocean.
  
  Sharks with this type of tail move their tail side to side in acute angles in what scientists consider classical motion. This generates forward motion well and also adds torque and lift that the shark has to counteract using their other fins. This is why the stabilizing effects of the pectoral and dorsal fins are so important.
Distinguishing Similar Dogfish
- Biologists use the caudal fin of dogfish to distinguish similar-looking subspecies. The smooth dogfish (Mustelus canis) and the narrow smooth hound (M. norrisi) are two closely related dogfish found in the southwest coasts of North and South America. They can be told apart by their caudal fins. M. canis has a sharply pointed lower lobe to the fin while M. norrisi has a rounded lower lobe. Even subspecies of M. canis can be told apart by their tail fins as the deeper-dwelling subspecies M. canis insularis has a longer caudal fin.

Animals & Science