shark

Sharks are a group of cartilaginous fish belonging to the class Chondrichthyes and the subclass Elasmobranchii. They have skeletons made of cartilage, five to seven gill slits on the head, and a streamlined body adapted for efficient swimming. There are about 500 shark species, inhabiting oceans worldwide and, in some cases, freshwater rivers and estuaries. They range from small species such as the dwarf lanternshark to the whale shark, the largest fish.

Anatomy and senses: Sharks have replaceable teeth in multiple rows, and their skeletons are cartilage rather than bone. They typically have two dorsal fins and a heterocercal tail. They rely on vision, the sense of smell, electroreception via the ampullae of Lorenzini, and the lateral line system to locate prey.

Ecology and life history: Diets vary; some sharks are apex predators feeding on marine mammals and large fish, while others are filter feeders like the whale shark and basking shark. Reproduction is via internal fertilization, with offspring produced through oviparity, ovoviviparity, or viviparity, and parental care is generally low.

Evolution and conservation: Sharks have existed for hundreds of millions of years, with fossil records dominated by teeth. Today, many populations face threats from overfishing, bycatch, and habitat loss, leading to species-specific protections and international management measures.