Sharks: The Basics

In short: Sharks are cartilaginous fish that have lived in the oceans for more than 400 million years. There are hundreds of species, from small bottom dwellers to the whale shark, the largest fish in the world.

In more detail: Their skeleton is made of cartilage instead of bone, and their skin is covered with tiny tooth-like scales. As predators at the top of many food chains, they are important for the balance of the marine ecosystem.

In detail

• Cartilage skeleton: Sharks share their light, flexible skeleton of cartilage with their close relatives, the rays (fische-und-meerestiere).
• Skin denticles: The skin is covered with small placoid scales that are built like miniature teeth and help water flow smoothly along the body while swimming.
• Conveyor-belt teeth: New rows of teeth keep growing behind the front teeth, so lost teeth are replaced continuously.
• Electrical sense: With fine, gel-filled pores on the head, the ampullae of Lorenzini, sharks sense the weak electrical fields produced by the muscles of their prey.
• Other senses: A keen sense of smell and the lateral line, which detects pressure waves in the water, help with orientation and hunting.
• Buoyancy without a swim bladder: Sharks have no swim bladder; a large, oil-rich liver provides part of their buoyancy.
• Breathing: Some species have to keep swimming so that water flows over their gills, while others can actively pump water through their gills even when resting.
• Reproduction: Fertilisation takes place inside the body; depending on the species, sharks lay eggs in tough capsules or give birth to live young, usually only a few at a time.
• Threats: Because many sharks mature late and have few offspring, overfishing and bycatch hit them hard, while attacks on humans are very rare (nahrungskette-und-oekosystem).