| Summary: | 碩士 === 東海大學 === 生物學系 === 88 === Respiration and ion regulation are the two principal functions of teleostean gills. Mitochondria-rich cells (MR cells; previously known as chloride cells) mainly distribute in the gill filaments of fish. The MR cells proliferate to increase the ionoregulatory capacity of the gill in response to osmotic challenges. Gill lamellae mainly consist of pavement cells, which are the major site of gas exchange. Some species also have MR cells in the gill lamellae. This will greatly increase the thickness of the blood-to-water diffusion barrier and thereby impede gas diffusion. There is definitely a trade-off between ionoregulation and gas diffusion. According to their habitats and life histories, freshwater fishes are further classified into primary, secondary and peripheral freshwater fishes. From previous literature, MR cells can be found in the lamellae of primary freshwater fish and some peripheral freshwater fish. On the contrary, secondary freshwater fish and other peripheral freshwater fish have no MR cells in the lamella. Fishes of Perciformes were chosen for this study because all three classes of freshwater fishes can be found in it. This study included two parts. The first part was to examine the distribution and morphology of MR cells in fishes. After examining 21 species from 9 families of Perciformes, found that the distribution pattern of lamellar MR cells was consistent to the previous observation. Several previous studies suggested that filament MR cells are considered to be the site for salt secretion in seawater, and lamellar MR cells are presumably responsible for ion uptake in fresh water. My study did not support this hypothesis. And, according to respiratory mechanism, fish are also classified into air-breathing fish and non-air-breathing fish. Most of primary freshwater fishes are also air-breathing fishes, while secondary freshwater fishes aren’t. Therefore, the correlation between air-breathing and MR cell distribution was evaluated. In the second part of study, fishes were acclimated in the 5 g/l artificial seawater and tap water, respectively, for one week, and the number of MR cells in filaments and lamellae examined. The study indicated that a strong association between the existence of air-breathing capacity and the functional difference of gill filaments and lamellae.
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