The swim bladder, gas bladder, fish maw, or air bladder is an internal gas-filled organ that contributes to the ability of many bony fish to control their buoyancy, and thus to stay at their current water depth without having to expend energy in swimming. Also, the dorsal position of the swim bladder means that the expansion of the bladder moves the center of mass downwards, allowing it to act as a stabilizing agent in some species. Additionally, the swim bladder functions as a resonating chamber, to produce or receive sound.
The swim bladder of a rudd
Internal positioning of the swim bladder of a bleak S: anterior, S': posterior portion of the air bladder œ: œsophagus; l: air passage of the air bladder
Swim bladder display in a Malacca shopping mall
Fish maw soup
Osteichthyes, also known as osteichthyans or commonly referred to as the bony fish, is a diverse superclass of vertebrate animals that have endoskeletons primarily composed of bone tissue. They can be contrasted with the Chondrichthyes and the extinct placoderms and acanthodians, which have endoskeletons primarily composed of cartilage. The vast majority of extant fish are members of Osteichthyes, being an extremely diverse and abundant group consisting of 45 orders, over 435 families and 28,000 species. It is the largest class of vertebrates in existence today, encompassing most aquatic vertebrates, as well as all semi-aquatic and terrestrial vertebrates.
Osteichthyes
Guiyu oneiros, the earliest known bony fish, lived during the Late Silurian, 425 million years ago. It has a combination of both ray-finned and lobe-finned features.
The ocean sunfish is one of the heaviest bony fish in the world.
Image: Carassius carassius