Olson K R, Ghosh T K, Roy P K, Munshi J S
Indiana University School of Medicine, University of Notre Dame 46635, USA.
Anat Rec. 1995 Jul;242(3):383-99. doi: 10.1002/ar.1092420311.
An ability to extract oxygen directly from the atmosphere enables air-breathing fish to survive otherwise debilitating hypoxic environments. Addition of accessory respiratory organs (ARO) necessitates changes in both the general circulatory system and the microcirculation of the respiratory epithelia. Understanding these modifications provides information on the efficiency of gas exchange organs as well as an indication of the evolutionary processes associated with adaptation to terrestrial habitats.
Vascular organization and structure of gills and ARO of the facultative air-breathing walking catfish Clarias batrachus were examined by scanning electron microscopy of vascular replicas and fixed tissue.
Well-developed filaments are present on all four pairs of gill arches and they possess three vascular pathways: respiratory (arterioarterial), nutrient (arteriovenous), and interlamellar (arteriovenous), typical of teleosts. ARO, consisting of gill fans, dendritic organs on the second and fourth gill arch, and the suprabranchial epithelium are derived from gill tissue and retain structural features and arterioarterial vessels similar to gill filaments. Gill and ARO vessels are in parallel with each other, and together they are in series with the systemic circulation. Nutrients and interlamellar vessels are reduced in ARO.
Other than the presence of multiple ventral aortas, and an additional vessel connecting the suprabranchial epithelium to the dorsal aorta, there are no vascular shunts or anatomical modifications that indicate spatial separation of flow through the heart or between gills and ARO. However, a mechanism is proposed that would prevent unsaturation of dorsal aortic blood by local myogenic vasoconstriction of gill vessels when the fish is in hypoxic water. Despite considerable differences in the gross features of ARO in Clarias and Heteropneustes fossilis (Olson et al. 1990 J. Morphol., 203:165), there are striking similarities in vascular organization and respiratory islet structure that suggest these ARO evolved in a common silurid ancestor and were later modified into an everted arborescent organ or inverted air sac, respectively.
直接从大气中提取氧气的能力使空气呼吸鱼类能够在原本会使其衰弱的低氧环境中生存。附属呼吸器官（ARO）的添加需要全身循环系统和呼吸上皮微循环的改变。了解这些变化可以提供有关气体交换器官效率的信息，以及与适应陆地栖息地相关的进化过程的线索。
通过对血管铸型和固定组织进行扫描电子显微镜检查，研究了兼性空气呼吸的胡子鲶（Clarias batrachus）鳃和ARO的血管组织和结构。
所有四对鳃弓上都有发育良好的鳃丝，它们具有三种血管途径：呼吸（动脉 - 动脉）、营养（动脉 - 静脉）和鳃小片间（动脉 - 静脉），这是硬骨鱼的典型特征。ARO由鳃扇、第二和第四鳃弓上的树状器官以及鳃上上皮组成，它们源自鳃组织，并保留了与鳃丝相似的结构特征和动脉 - 动脉血管。鳃和ARO血管相互平行，并且它们与体循环串联。ARO中的营养血管和鳃小片间血管减少。
除了存在多个腹主动脉以及一条将鳃上上皮连接到背主动脉的额外血管外，没有血管分流或解剖学改变表明流经心脏或鳃与ARO之间的血流存在空间分离。然而，提出了一种机制，当鱼处于缺氧水中时，通过鳃血管的局部肌源性血管收缩来防止背主动脉血液不饱和。尽管胡子鲶和印度囊鳃鲶（Olson等人，1990年，《形态学杂志》，203:165）的ARO总体特征存在相当大的差异，但在血管组织和呼吸胰岛结构方面存在惊人的相似之处，这表明这些ARO在一个共同的鲇形目祖先中进化，后来分别演变成外翻的树状器官或倒置的气囊。
