elasmobranchs

Elasmobranchs are a group of cartilaginous fishes that includes sharks, rays, skates, and sawfishes. They belong to the subclass Chondrichthyes, along with the chimaeras (holocephali), and have a long fossil history that stretches back hundreds of millions of years. They inhabit many marine environments worldwide and, in some cases, brackish or freshwater systems.

A defining feature of elasmobranchs is their skeleton made of cartilage rather than bone. They possess placoid skin, a series of gill slits on the sides of the head, and paired pectoral fins. Most have highly developed senses, including electroreception via the ampullae of Lorenzini and a keen sense of smell. Males reproduce through internal fertilization using claspers, and elasmobranchs display a range of reproductive strategies from oviparity (egg-laying) to viviparity (live birth), with some species retaining embryos internally for extended periods.

Ecology and behavior vary widely within the group. Large filter-feeding sharks such as the whale shark and basking shark feed on plankton, while many sharks are active predators of fish and marine mammals. Rays and skates are typically benthic, feeding on invertebrates and small prey items. Sawfishes use their elongated snouts to probe for prey along coastal waters. Most elasmobranchs are long-lived and grow slowly, with late maturity, factors that influence their population recovery after depletion.

Conservation concerns are significant. Overfishing, bycatch, fins processing, and habitat loss threaten many species, leading to numerous IUCN listings as vulnerable or endangered. Protected areas, improved bycatch mitigation, and international trade controls aim to safeguard elasmobranch diversity for the future.