What are Sharks & Rays?
Sharks & Rays are FISH, but they are very special fish, they are cartilaginous fish! This means their skeletons are made of cartilage (you’ll be able to read more about this below). Sharks & Rays are in one of two sub-classes of cartilaginous fish, they are in the sub-class Elasmobranchii which currently contains around 1,000 extant species which can be further classified into around 400 species of sharks and 600 species of rays.
Sharks first appeared in the fossil record over 400 million years ago, nearly 300 million years before the dinosaurs! They occupy almost every marine ecosystem on earth and some can survive in freshwater, although no species lives there exclusively.
Common features of members of the elasmobranchii sub-class are:
- they have no swim bladders
- they have five to seven pairs of gill slits (see gill info below)
- they have rigid dorsal fins (see fins info below)
- they have small placoid scales (see skin info below)
- their teeth are in several series (see teeth info below)
- their eyes have a tapetum lucidum
- the inner margin of each pelvic fin in the male fish is grooved to constitute a clasper for the transmission of sperm
- these fish are widely distributed in tropical & temperate waters
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So Sharks & Rays are closely related. Rays can be distinguished by their flattened bodies, enlarged pectoral fins that are fused to the head, and gill slits that are placed on their ventral surfaces. Therefore much of the information below relates equally to Rays as it does to Sharks. The following information has been kindly provided by The Shark Trust. The Shark Trust is the UK charity for shark conservation. The trust works to advance the worldwide conservation of sharks through science, education, influence and action. Find out more by visiting www.sharktrust.org. Learn about Shark ID from the Shark Trust.
The main characteristics that define a shark are:
Bony fish such as tuna and mackerel have a skeleton that is made out of bone just like a human skeleton. A shark skeleton is made entirely of cartilage (gristle). The same material as human noses and ears are made of. It is lighter than bone, helping the shark stay afloat. It is also more bendy than bone and grows as the shark does.
Most bony fish have flat scales covering their body, which grow with the fish. The skin of sharks is much rougher than that of other fish as it is covered with millions of tiny teeth called dermal denticles. These denticles point backwards and help the shark to swim faster by reducing the water turbulence. As a shark grows the denticles are shed and replaced with slightly larger ones. Some denticles are so big that the shark uses them as defensive spines or shields.
Shark fact: The hydrodynamic efficiency of shark skin has been copied by swimming costume manufacturers, such costumes are said to reduce swimmers times.
Visit Support out Sharks for some fantastic, fun & very informative infographics about sharks
A shark’s teeth are larger versions of the denticles covering a shark’s body. Teeth are arranged in rows, which slowly move forward from the back of the jaw (a bit like a conveyor belt). As the front rows of teeth wear down or fall out new rows move from behind to replace them. These replacements happen about every two weeks.
Different sharks have different shaped teeth depending on what food they eat. Sharks that eat shellfish and crabs have flat crushing teeth. Sharks that eat fish have pointed teeth and those that sometimes eat seals and sea lions have razor sharp teeth. Filter feeding sharks (Whale (Rhincodon typus), Basking (Cetorhinus maximus) and Megamouth (Megachasma pelagios) have greatly reduced teeth. They use gill rakers to strain plankton from the water.
The Save our Seas Foundation Shark Centre – A great place to visit and learn more about Sharks
The SOSF Shark Centre was established in Cape Town, South Africa, in 2008 to encourage the conservation and awareness of sharks and marine life in the False Bay area. The Shark Centre is committed to conducting valuable research while at the same time offering public educational programmes to change myths and people’s misperceptions of these important creatures.
Why this is important: Sharks are vital to the health of our oceans. They play an important role in the ocean by regulating the quantity and health of other species of fish and invertebrates, keeping the ecosystem in balance.
Bony fish and sharks have fins that help them swim properly. Bony fish have fins that fold down when they are not being used. Sharks have five pairs of rigid fins, which can’t fold down. The big triangular dorsal fin of the shark is the first part you see if the shark is at the surface. This fin helps the shark to balance itself. A shark’s tail is called the caudal fin and this fin varies in shape between different sharks. Sharks move their caudal fin from side to side to push themselves forward. They steer with their pectoral (side) fins.
- Shortfin Mako Sharks (Isurus oxyrinchus) are the fastest sharks and they can move at speeds of up to 69kph .
- Sharks can’t swim backwards like some fish can.
Looking for a career or experience working in shark conservation? Check out our Wise Work job pages!
Sharks and rays have 5 to 7 gill slits. As a shark swims forward, water passes over its gills. Oxygen in the water is absorbed into tiny blood vessels near the gill. The blood carries the oxygen around the body.
Some sharks can pump water across their gills. The shark opens its mouth to drawn water in then shuts its mouth. Water is squeezed over the gills as more water is sucked into the mouth. Valves stop water going down the throat, small gill flaps stop water coming in through the gill slits. To aid the water flow sharks swim forward all the time, if they are trapped for any reason they cannot breathe properly.
Sharks that live in the open ocean depend on swimming forward for their buoyancy as well as to breathe, if they cannot swim they sink and suffocate. Wobbegong and other bottom living sharks do not have to keep swimming, they breathe in through their spiracle holes and out through their gills slits just like skates and rays.
Sink or swim
A shark’s body tissues are denser and heavier than water so it is natural for a shark to slowly sink to the seabed. Sharks have various buoyancy aids to stop this happening. Sharks reduce sinking by having a big oily liver and light, cartilage skeleton. Some sharks can stop swimming as they continue to actively move water over their gills. Sharks like the Whitetip Reef Shark have been seen resting on the seabed near reefs. Unlike bony fish sharks do not have a swim bladder, however, some sharks gulp air into the gut as a very primitive swim bladder.
Fertilization is internal. Development is usually live birth (ovoviviparous species) but can be through eggs (oviparous). Some rare species are viviparous. There is no parental care after birth; however, some Chondrichthyes do guard their eggs.
Sharks have two kinds of skeletal muscle (muscle that moves the skeleton). The first is a thin layer of red muscle, which lies just under their skin. This red muscle has a good blood supply and helps the shark to swim slowly for a long time. Red muscle works by breaking down the fat in the shark’s body. The second type is white muscle, found under the red muscle. White muscle has a poor blood supply and works by using the energy from the breakdown of glycogen (sugars). Sharks use their white muscle to make short fast sprints when catching prey or moving away from danger.
Most fish are cold blooded; their body temperature is the same as the surrounding water. Mako (Isurus oxyrinchus), White (Carcharodon carcharias), Porbeagle (Lamna nasus) and thresher sharks (Alopias vulpinus) are all warm blooded and can control their own body temperature, like birds and mammals. Their body temperature can sometimes be about 10°C above the surrounding water temperature.
Sharks use these amazing adaptations to dominate the world’s oceans. They are now threatened by human activities such as shark finning, overfishing and accidental by-catch.
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Visit Support out Sharks for some more fantastic, fun & very informative infographics about sharks
Click on the infographic below for a clearer image
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