elasmobranch

Elasmobranchs are a subgroup of cartilaginous fishes in the class Chondrichthyes, including sharks, rays, skates, and sawfishes. They are characterized by a skeleton made of cartilage rather than bone, paired fins, five to seven exposed gill slits on the head, and placoid dermal denticles that give their skin a rough texture. Most have replaceable teeth and a highly developed array of senses, notably electroreception through the ampullae of Lorenzini and a lateral line system that detects movement and vibration.

Anatomical diversity ranges from streamlined, fast-swimming sharks to flattened rays and skates, and to elongated sawfishes with rostrums. Reproduction is internal, with fertilization occurring in the female. Modes of reproduction vary: some species are oviparous (egg-laying), others ovoviviparous or viviparous (live-bearing). In many species, embryos feed on yolk, while others receive additional maternal nutrition through yolk-sac placentas or related structures.

Elasmobranchs are found in oceans worldwide, from shallow coastal waters to the deep sea, and some species tolerate brackish or even freshwater environments. They occupy a range of ecological roles, from apex and mesopredators to filter-feeding rays that strain plankton from the water. Their life histories tend to be slow, with relatively long lifespans, late maturity, and low reproductive output compared with many other fishes.

Many elasmobranch species face population declines due to overfishing, bycatch, and demand for shark fins and other products. Conservation measures include fisheries management, gear modifications to reduce bycatch, protected areas, and international trade controls under agreements such as CITES.