| The Shark fish Quick Facts | |
|---|---|
| Name: | The Shark fish |
| Scientific Name: | Euselachii |
| Calories | 194 Kcal./cup |
| Major nutrients | Selenium (52.55%) Isoleucine (44.08%) Vitamin B-12 (42.92%) Lysine (41.54%) Tryptophan (40.91%) |
The earliest known sharks date back to 420 million years ago. Sharks have been diversified into more than 500 species. It ranges in size from small dwarf Etmopterus perryi (dwarf lanternshark), a deep-sea species of 6.7 inches (17 centimeters) in length, to the Rhincodon typus (whale shark), the largest fish in the world reaching 40 ft (12 metres) in length. They are found in all seas and common to depths of 6,600 ft (2,000 meters). Generally, they do not live in freshwater though there are few known exceptions such as river sharks and bull sharks that can survive or could be found in both freshwater and seawater. It has dermal denticles which protect skin from damage or parasites including the improvement in fluid dynamics. It has various sets of replaceable teeth. The teeth are embedded in gums than affixed to the jaw and are replaced constantly throughout life. The replacement of a tooth varies from every 8 to 10 days to several months. The shape of tooth depends on the diet: those feeding on crustaceans and mollusks have flattened and dense teeth used to crush and those feeding on fish have needle-like teeth to grip and those who fed on larger prey such as mammals have pointed lower teeth required for gripping and triangular upper teeth having serrated edges for cutting. Basking sharks which is plankton feeders have small and non-functional teeth. The species well known are tiger shark, great white shark, thresher shark, mako shark, blue shark, and hammerhead shark are apex predators at top of the underwater food chain.
Body
Sharks have a torpedo-shaped body with stiff two-side fins and a curved tail that helps the shark swim. The shark’s body is covered by small scales that make the skin very rough. Most sharks have a mouth at the bottom of the head. It has sharp, pointed many rows of teeth. The older ones are replaced by new teeth as often as every week. Sharks have 5 to 7 gills behind eyes on each side of the head that is used to breathe underwater. They have sharp senses and could find their prey by the sound it makes.
Skeleton
Its skeletons differ from bony fish or terrestrial vertebrates. Sharks have skeletons that are made of connective tissue and cartilage. Cartilage is durable and flexible however half the normal density of bone is. It reduces the skeleton’s weight and saves energy. As the sharks do not have rib cages, they could be crushed easily under their own weight on land.
Jaw
Rays and skates (jaws) of sharks are not attached to the cranium. The surface of the jaw requires extra support because of its heavy exposure to physical stress and its requirement for strength. It has a layer of tesserae, crystal blocks of calcium salts which is arranged as a mosaic. It provides the same strength to these areas like bony tissue found in other animals. Generally, they have one layer of tesserae but bull shark, the great white shark, and tiger shark have 2 to 3 layers depending on the size of the body. The jaw of a large great white shark has five layers. The snout has spongy and flexible cartilage to absorb the power of impacts.
Fins
The skeleton of fins is elongated and is supported with soft or unsegmented rays called ceratotrichia, filaments of elastic protein that resembles horny keratin in hair or feathers. Mostly, sharks have eight fins. They could drift away from objects in front of them as their fins do not allow them to move in a tail-first direction. They have a complex dermal corset which is made of flexible collagenous fibers or arranged as a helical network surrounding its body. It acts as an outer skeleton that provides attachment for its swimming muscles and saves energy. Its dermal teeth provide hydrodynamic advantages that lower turbulence when swimming.
Tails
Tails support thrust, make speed or accelerates dependent on tail shape. The shape caudal fin considerably varies between shark species due to its evolution in separate environments. It possesses a heterocercal caudal fin in which the dorsal portion is usually larger than the ventral portion. It is as the shark’s vertebral column extends to a dorsal portion that provides greater surface area for attachment of muscles. It allows effective locomotion among negatively buoyant cartilaginous fish. Most bony fish acquire homocercal caudal fin.
Tiger sharks have a large upper lobe allowing for slow cruising and outbreak of speed. It must be able to twist & turn easily in water when hunting in order to support a varied diet. The Porbeagle shark has a large lower lobe that hunts schooling fish such as herring and mackerel to assist keep pace having its fast-swimming prey. The tail adaptations assist sharks to catch prey more directly such as the usage of thresher sharks for their powerful and elongated upper lobe amaze fish and squid.
Reproduction
They are K-selected reproducers i.e. they produce a small number of well-developed young aversed to a large number of poorly developing young. Its fecundity ranges from 2 to more than 100 young per reproductive cycle. In comparison to other fish, sharks mature slowly.
Feeding
Sharks are carnivorous. Basking sharks, megamouth sharks, and whale sharks have evolved independently different strategies for filter-feeding plankton. Basking sharks form ram feeding, whale sharks use suction to take in small fishes, and plankton and megamouth sharks make suction feeding with the use of luminescent tissue inside their mouths for attracting prey in the deep ocean. This type of feeding needs gill rakers—long, slender filaments which form efficient strainer—analogous to the baleen plates of great whales. Shark catches plankton in these filaments & swallows from time to time in enormous mouthfuls. These species have small teeth because they are not required for feeding. The great white shark is not an apex predator like many other sharks.
Seabed dwelling species are effective ambush predators. Wobbegongs and angel sharks use camouflage lie in wait and inhale prey into their mouths. Benthic sharks feed solely on crustaceans which are crushed with their flat molariform teeth. Sharks feed on fish or squid which are swallowed whole. Viper dogfish could be point outwards to strike and capture prey which is then swallowed intact. Thresher sharks use their long tails to shock shoaling fishes and either stirs prey from the seabed and slash at swimming prey with its tooth studded rostra. Sharks such as whitetip reef sharks are cooperative feeders and hunt in packs to herd or capture elusive prey. It is often migratory and travels huge distances around ocean basins in large schools.
Behavior
More than half of the sharks are not harmful to people and occasionally attacks them. The white shark is the most dangerous fish with sharp teeth which could rip off chunks of flesh from animals. It hunts tuna, sea lions, and other sharks. Even they have attacked human beings notably when they are worried and hungry. Noises, movement, and blood in the water provoke sharks and make them attack.
Range and habitat
They are found in all seas. Generally, they do not live in freshwater exceptionally bull sharks and river sharks that could swim both in freshwater and seawater. Commonly, they are found in depths of 2000 meters and some live even deeper but are absent below 3000 meters. The report confirmed that Portuguese dogfish are found at deep 3700 meters (12100 ft).
