About Shark Physiology

What are sharks?

Sharks belong to the group chondrichthyes, which are fish with the following characteristics: jaws, paired fins, paired nostrils, and a skeleton made of cartilage. Sharks along with most chondrichthyan fishes, such as stingrays, electric rays, skates, sawfish, and guitarfish, are collectively known as elasmobranchs.

Does the shark have a skeleton?

Yes! A shark's skeleton is made mostly of cartilage that can be strengthened by deposits of minerals in areas subjected to special stress such as the jaws and vertebrae. Cartilage is an ideal tissue for shaks for several reasons. First, cartilage is lighter than bone, important for sharks which have no swim bladder to help with buoyancy. Second, cartilage is a relatively flexible material, giving tensile force to swimming and turning movements. Lastly, cartilage can grown throughout the life of a shark.

How are sharks shaped?

Most sharks are characterized by a fusiform (rounded and tapering at both ends) body. This streamline, cylindrical body shape reduces drag and requires a minimum of energy to swim. Some exceptions to the "typical" shark body shapes are the angelsharks and the carpetsharks.

Do sharks come in different colors?

Yes. Most sharks are generally drably countershaded, meaning the dorsal side (top) is darker than the ventral side (bottom), but sharks come in many colors, from cream to brown to dark grey. The dark top of the countershaded shark blends in with the dark ocean depths when viewed from above. The light bottom blends in with the lighter surface of the sea when viewed from below. As a result, predators or prey do not see a contrast between the countershaded shark and the environment.

How do sharks use their fins?

Sharks have five different kinds of fins. Paired pectoral fins lift the shark as it swims. Paired pelvic fins as well as one or two dorsal fins stabilize the shark. A single anal fin provides stability in some species where it is present. The caudal or tail fin propels the shark. Sharks, as all fish, use their body and tail in a side to side motion.

Do sharks have scales?

Yes. Sharks, like all elasmobranchs, have placoid scales, also called dermal denticles. Placoid scales have the same structure as a tooth, consisting of three layers: an outer enamel layer, dentine, and a central pulp cavity. Placoid scales do not get larger as the shark grows; instea, the fish grows more scales. The placement of th eplacoid scales reduces tehe friction of the water for fast moving sharks by channeling the water flow over the body.

What about sharks' teeth?

Sharks' teeth are in parallel rows. Several rows of replacement teeth develop continuously throughout life behind the outer row of functional teeth. A degree of feeding specialization is evidenced by the shape and size of the teeth. Thin, pointed teeth, are for grabbing and holding prey; serrated, wedge-shaped teeth are good for cutting; and smalle conical teeth are great for crushing the shells of crabs and mollusks for bottom dwelling sharks.

Do sharks have nostrils?

Yes! Sharks have paired external nostrils on the underside of the snout. These nasal chambers are used only for smell, not for obtaining oxygen.

How many gills does a shark have?

Sharks can have five to seven gills slits on each side. As water passes over the gills, oxygen is absorbed by blood in the gills. Some sharks have small openings called spiracles behind the eyes at the top of teh head. Spiracles are rudimentary first gill slits and are reduced or absent in most active, fast-swimming sharks.