Gas gland

...There are two types of fish: those in which the airway formed during the development of the swim bladder remains there throughout life, connecting the swim bladder to the digestive tract (salmon, sardines, carp, eels, etc.), and those in which the airway disappears secondarily and there is no connection between the two (sea bass, red sea bream, Pacific cod, etc.). In swim bladders that lack an airway, a red gland (gas gland) consisting of a collection of capillaries develops in part of the wall, and secretes gases (carbon dioxide, oxygen, nitrogen, etc.) from the blood to regulate the amount of gas in the swim bladder. The swim bladder is not only involved in buoyancy regulation, but in some species it can also be involved in hearing and water pressure sensation, and some fish, such as rockfish and croaker, make sounds by vibrating the swim bladder wall. ...

*Some of the terminology that refers to "gas glands" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…うきぶくろの発生時にできた気道が終生存在してうきぶくろと消化管の間に連絡がある型(サケ，マイワシ，コイ，ウナギなど)と，気道が二次的に消失して両者の連絡がなくなる型(スズキ，マダイ，マダラなど)とがある。気道を欠くうきぶくろでは壁の一部に毛細血管の集合した赤腺red gland(ガス腺)が発達し，血液中のガス(二酸化炭素，酸素，窒素など)を分泌してうきぶくろ内のガス量を調節する。うきぶくろは浮力調節に関与するだけでなく，種類によっては聴覚や水圧感覚に関与することもあり，カサゴやニベのように鰾壁（ひようへき）を振動させて発音する魚もある。…

※「ガス腺」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報