Tomita Taketeru, Nakamura Masaru, Sato Keiichi, Takaoka Hiroko, Toda Minoru, Kawauchi Junro, Nakaya Kazuhiro
Hokkaido University Museum, Hakodate, Hokkaido, Japan.
Okinawa Churashima Research Center, Okinawa Churashima Foundation, Motobu, Okinawa, Japan.
PLoS One. 2014 Oct 20;9(10):e109504. doi: 10.1371/journal.pone.0109504. eCollection 2014.
Respiration in fishes involves buccal pumping, which is characterized by the generation of nearly continuous water flow over the gills because of the rhythmic expansion/compression of the pharyngeal cavity. This mechanism is achieved by the functions of the vascular, skeletal, and muscular systems. However, the process by which the embryo establishes the mechanism remains a mystery. Morphological and kinematical observations on captive cloudy catsharks, Scyliorhinus torazame, have suggested that the embryo starts buccal pumping just before the respiratory slits open on the egg capsule. During the pre-opening period, the embryo acquires oxygen mainly via the external gill filaments. After slit opening, respiration of the embryo involves buccal pumping to pass water over the "internal gills." The onset of buccal pumping accompanies four morphological changes: (1) regression of the external gill filaments, (2) development of blood vessels within the "internal gills," (3) completion of the development of hyoid skeletal and muscular elements, and (4) development of the oral valve. A previous study showed that buccal pumping allows the embryo to actively regulate oxygen intake by changing the pumping frequency. Thus, establishment of buccal pumping in the egg capsule is probably important for embryo survival in the unstable oxygen environment of the egg capsule after slit opening.
鱼类的呼吸涉及口腔泵吸，其特点是由于咽腔有节奏地扩张/压缩，在鳃上产生几乎连续的水流。这种机制是通过血管、骨骼和肌肉系统的功能实现的。然而，胚胎建立这种机制的过程仍然是个谜。对圈养的云纹猫鲨（Scyliorhinus torazame）进行的形态学和运动学观察表明，胚胎在卵囊上的呼吸孔打开之前就开始口腔泵吸。在呼吸孔打开之前的时期，胚胎主要通过外鳃丝获取氧气。呼吸孔打开后，胚胎的呼吸涉及口腔泵吸，以使水流过“内鳃”。口腔泵吸的开始伴随着四种形态变化：（1）外鳃丝退化，（2）“内鳃”内血管发育，（3）舌骨骨骼和肌肉成分发育完成，（4）口瓣膜发育。先前的一项研究表明，口腔泵吸使胚胎能够通过改变泵吸频率来主动调节氧气摄入量。因此，在卵囊中建立口腔泵吸可能对呼吸孔打开后卵囊不稳定氧气环境中的胚胎存活很重要。
