Brauner C J, Matey V, Wilson J M, Bernier N J, Val A L
Department of Zoology, University of British Columbia, 6270 University Blvd, Vancouver, BC, Canada, V6T 1Z4.
J Exp Biol. 2004 Apr;207(Pt 9):1433-8. doi: 10.1242/jeb.00887.
The transition from aquatic to aerial respiration is associated with dramatic physiological changes in relation to gas exchange, ion regulation, acid-base balance and nitrogenous waste excretion. Arapaima gigas is one of the most obligate extant air-breathing fishes, representing a remarkable model system to investigate (1) how the transition from aquatic to aerial respiration affects gill design and (2) the relocation of physiological processes from the gills to the kidney during the evolution of air-breathing. Arapaima gigas undergoes a transition from water- to air-breathing during development, resulting in striking changes in gill morphology. In small fish (10 g), the gills are qualitatively similar in appearance to another closely related water-breathing fish (Osteoglossum bicirrhosum); however, as fish grow (100-1000 g), the inter-lamellar spaces become filled with cells, including mitochondria-rich (MR) cells, leaving only column-shaped filaments. At this stage, there is a high density of MR cells and strong immunolocalization of Na(+)/K(+)-ATPase along the outer cell layer of the gill filament. Despite the greatly reduced overall gill surface area, which is typical of obligate air-breathing fish, the gills may remain an important site for ionoregulation and acid-base regulation. The kidney is greatly enlarged in A. gigas relative to that in O. bicirrhosum and may comprise a significant pathway for nitrogenous waste excretion. Quantification of the physiological role of the gill and the kidney in A. gigas during development and in adults will yield important insights into developmental physiology and the evolution of air-breathing.
从水生呼吸到空气呼吸的转变与气体交换、离子调节、酸碱平衡和含氮废物排泄等方面的显著生理变化相关。巨骨舌鱼是现存最依赖空气呼吸的鱼类之一，是研究以下两个方面的出色模型系统：（1）从水生呼吸到空气呼吸的转变如何影响鳃的结构；（2）在空气呼吸进化过程中生理过程从鳃向肾脏的转移。巨骨舌鱼在发育过程中经历从水呼吸到空气呼吸的转变，导致鳃形态发生显著变化。在小鱼（10克）中，鳃在外观上与另一种密切相关的水呼吸鱼类（双须骨舌鱼）定性相似；然而，随着鱼的生长（100 - 1000克），鳃小片间隙充满细胞，包括富含线粒体的（MR）细胞，仅留下柱状鳃丝。在此阶段，鳃丝外细胞层有高密度的MR细胞以及强烈的Na(+)/K(+)-ATP酶免疫定位。尽管鳃的总表面积大幅减少，这是专性空气呼吸鱼类的典型特征，但鳃可能仍然是离子调节和酸碱调节的重要部位。相对于双须骨舌鱼，巨骨舌鱼的肾脏大幅增大，可能构成含氮废物排泄的重要途径。量化巨骨舌鱼发育过程中和成年期鳃和肾脏的生理作用，将为发育生理学和空气呼吸的进化提供重要见解。
