Daxboeck C, Barnard D K, Randall D J
Respir Physiol. 1981 Mar;43(3):349-64. doi: 10.1016/0034-5687(81)90115-8.
The bowfin, Amia calva is a facultative air breathing fish restricted to North America and is reported to estivate. The relative and functional gill surface areas of A. calva are not reduced, as in many amphibious fish, but have areas comparable to many completely aquatic species. The secondary lamellae are fused to form a lattice-work of rectangular pores, a gill arrangement unique among fresh-water fishes. This highly modified gill structure imparts considerable rigidity such that these do not collapse upon air exposure. In vivo blood gas measurements from air exposed Amia reveal that these gills must be free of water, since there is both O2 uptake and CO2 excretion across them. The observed ventilatory motions therefore pass air over the secondary lamellae for diffusive gas exchange during air exposure. In the artificial conditions of our experiments, however, air exposure was associated with a marked acidosis and the fish died within 2 hours of being returned to normoxic water.
弓鳍鱼（Amia calva）是一种仅限于北美的兼性空气呼吸鱼类，据报道会夏眠。与许多两栖鱼类不同，弓鳍鱼的相对鳃表面积和功能鳃表面积并未减少，而是与许多完全水生的物种相当。次生鳃小片融合形成矩形孔的格子状结构，这种鳃的排列在淡水鱼中是独一无二的。这种高度改良的鳃结构赋予了相当大的刚性，使其在暴露于空气时不会塌陷。对暴露于空气中的弓鳍鱼进行的体内血气测量表明，这些鳃必须无水，因为在鳃上既有氧气摄取又有二氧化碳排出。因此，观察到的通气运动在空气暴露期间使空气流过次生鳃小片以进行扩散性气体交换。然而，在我们实验的人工条件下，空气暴露与明显的酸中毒有关，并且鱼在回到常氧水中2小时内死亡。
