Scientific Name Chondrichthyes Cartilaginous Fish Scientific Name Chondrichthyes

External Physical and Specialized Traits Placoid scales also called dermal denticles. Multiple gill slits. Nostrils on both sides of the head. Teeth are not fused to the jaw. These fish have dorsal fins, an anal fin, a pair of ventral fins and a single caudal fin.

Gas Exchange Cartilaginous fish exchange gas through their gills which are slits in the side of their bodies. These fish normally have five slits on each side of their body. Compared to the bony fish, cartilaginous fish are less efficient when it comes to gas exchange, because they don’t have a mechanism that pushes water over their gills, so they always have to be moving. Cartilaginous fish also have parallel flowing blood in their gills, meaning their blood flows in the same direction as the water. This means only 50% oxygen concentration is reached in the blood, compared to countercurrent flow (bony fish), where blood flows in the opposite way that the water does, meaning the blood can be more saturated with oxygen.

Cartilaginous Fish Bony Fish

Circulatory System Cartilaginous fish, like humans, have a closed circulatory system. The heart is made up of two chambers, where the blood flows from the heart, through the ventral aorta, to the gills. It is then oxygenated and flows to the rest of the body via the dorsal aorta, before returning to the heart and repeating the cycle.

Digestive system The intestines of cartilaginous fish are much shorter than those of mammals. Their stomachs lead to spiral valves, which are twisted to create a larger surface area which increases nutrient absorption. Because of the spiral valve, sharks cannot digest large items such as bones through their lower intestine, so they remain in the stomach until broken down. Sharks keep food in their intestine long enough to absorb the maximum amount of nutrients, so they don’t feed very often. The food passes through the short colon of the shark, almost digested and then out the cloaca.

Nervous system Cartilaginous fish have a very complex brain. There are three mains sections of their brains : one for smell, one for vision and motor responses, and one that controls movement and balance. Cartilaginous fish experience sense much differently than many other organisms. They have ampullae of lorenzini which are organs that allow them to sense electric fields, pressure changes and vibrations. Beneath the exterior pore is a jelly-filled canal, filled with sensory cells that send electric signals to the nervous system. Ampullae Lorenzini can be used for hunting to detect the weak electric fields of fish in distress, and can also detect change in water temperature.

Ampullae of Lorenzini fd

A Brief Look At the Excretory System Sharks and other cartilaginous fish store large amounts of urea in their blood. Special cells in the rectal gland of these fish excrete whatever excess salt does enter the system. System includes 2 kidneys, 2 ureters, a bladder and a urinary opening. Similar to human excretory system.

Reproduction All cartilaginous fish eggs are produced by the female, and are fertilized internally. Claspers are found on the male, which are used to channel semen into the female’s cloaca. Once the egg is fertilized, the female will either lay those eggs, or give live birth.

Movement Even when they’re sleeping, Cartilaginous fish must continue swimming or they will sink. This is because they don’t have an air-filled swim bladder like most bony fish. The movement of cartilaginous fish varies between species. A shark’s caudal fin propels it forward, the dorsal fin provides balance, and the pectoral fins are used for upward force.

Dorsal fin Back Dorsal Fin Caudal Fin Pectoral Fin Pectoral Fin

Movement Cont’d The movement of a ray fish is different than a shark. A ray’s flat body is made of pectoral fins joined by a head and trunk. They beat the pectoral fins in a wave motion to propel them forward.

Some Fun Facts Found in both fresh and saltwater. Chondrichthyans lack the air-filled swim bladder found in most bony fish, and therefore must swim continuously to stay afloat, buoyancy is assisted by light oils. The physiology of Chondrichthyan is of interest to cancer researchers because the cartilage of chondrichthyans contains substances known to inhibit the growth of tumors. A keen sense of hearing allows sharks to locate prey from as far away as 250 meters (800 feet).

Some More Fun Facts As in many nocturnal mammals, the inside of a shark's eye is covered with a tapetum , a membrane that reflects light back into the eye. Unlike most fish, sharks can reduce and expand their pupils. Sharks can detect electrical signals via the ampullae of Lorenzini, which are specialized organs distributed over a shark's head that detect changes in electrical currents. Sharks use these to sense the electrical fields emitted by the heart and muscles of their prey.