| Summary: | 碩士 === 東海大學 === 生命科學系 === 93 === Non-air-breathing and air-breathing are two respiratory modes in fishes. The air-breathing fish can be further divided into the amphibious and the aquatic air-breathing fish. The aquatic air-breathing fish has specialized accessory air-breathing organ. Fish gill is a multifunctional organ and is responsible for at least gas exchange and ionic regulation. By modifying their gill morphologies and functions, fishes are adaptive to various environmental stresses. For the aquatic air-breathing fish, most studies focused on the morphology of the gill vascular system. There was no evidence whether the morphological plasticity directly relates to their functional differentiation. Nevertheless, most studies on the enzyme activity for the ionic regulation focused only on a particular pair of gills. No study was conducted to examine the four pairs of gills simultaneously. The experiment hypothesis is that aquatic air-breathing fish with labyrinthine organ has both morphological plasticity and functional differentiation in the gills. The first and the second gills have the morphological and functional plasticity and were responsible for ionic regulation stress; the third and the fourth gills become specialized for the transport of oxygenated blood, and are less plastic to environmental stress. The experimental species was the aquatic air-breathing fish, Trichogaster leeri. I investigated several morphmetric parameters and the histological examination to test the morphological plasticity of the gills, and used the Na+, K+-ATPase ESA to test the functional differentiation of the gills. The morphological plasticity were found in various aspects, including the gross anatomy of gills, the filament density, the length of the gill arch, the length of the filaments and the length of the lamellae of the each gill arch in fish. There were swelling chambers, presumably blood vessels, in the fourth gill arch and this implied that the morphology of the fourth gill could be specialized for the transport of oxygenated blood. Further, the number of mitochondria-rich cells in the first and the second gills increased upon an ionic stress, whereas no difference was found in the third and the forth gills. This phenomenon suggested that there were functional difference between the anterior and the posterior gills. The variation in the Na+, K+-ATPase ESA demonstrated that the anterior and the posterior gills differ in their abilities to ionic stress. The Na+, K+-ATPase ESA was higher in the first and the second gills upon transferred to 5 g/L and deionized water, respectively, for 4 days. These imply that the gills of the aquatic air-breathng fish have the functional differentiation. These results support the hypothesis that both morphological plasticity and functional differentiation can be found in the gills of the aquatic air-breathing fish, Trichogaster leeri. And, the plasticity of each gill was different in ionic stress.
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