ikan

Ikan, the Indonesian word for fish, refers to aquatic, gill-bearing vertebrates that live in water and are typically covered with scales. Fish represent one of the largest and most diverse groups of vertebrates, occupying a wide range of aquatic environments from fast rivers to open oceans and deep seas.

Classification and diversity. Modern classifications separate jawless fish (such as lampreys), cartilaginous fish (sharks and rays), and bony fish. Bony fish (Osteichthyes) constitute the largest group, with thousands of species described and many more yet to be documented. They differ in morphology, feeding, and reproductive strategies.

Anatomy and physiology. Common features include gills for respiration, fins and a tail for propulsion, and scales along the body. Most fish are ectothermic (cold-blooded) and rely on water for oxygen; some species possess adaptations such as a swim bladder or lung-like organs.

Ecology and life cycles. Fish occupy every aquatic niche, from microscopic plankton feeders to apex predators. Reproduction varies, with eggs released into water, live birth in some species, and complex parental care in others. Many species form schools or migrate long distances.

Human use and conservation. Fish are a crucial source of protein for many communities and support global fisheries and aquaculture. They face pressures from overfishing, bycatch, pollution, and habitat degradation. Sustainable management, protected areas, and responsible aquaculture aim to reduce ecological impacts.