碩士 / 國立臺灣大學 / 動物學研究所 / 90 / Developing fish larvae, whose organs are poorly or under developed, have to maintain ionic homeostasis in their body fluids. However, little is known about how fish larvae regulate their Cl- balance in hypotonic freshwater environments. The purpose of present study was to investigate the mechanism how developing larvae regulate their Cl- balance upon challenges with low-Cl- environments. Moreover, euryhaline tilapia (Oreochromis mossambicus) and ayu (Plecoglossus altivelis), and stenohaline goldfish (Carassius auratus) are different in habitats and life histories. The present paper was also to test whether these species develop different strategies for acclimation to diluted external media. Embryos were incubated in artificial fresh water with normal (0.4 mM) or low (0.04 mM) Cl- from eyed-egg stage to 5 d post-hatching (H5). Whole-body Cl- content and Cl- influx were measured to determine the Cl--balance capacities. Moreover, the Cl- uptake kinetics was measured in 3-d-old (H3) larvae acclimated to normal- and low-Cl- water. In addition, 0-d-old (H0) tilapia larvae were transferred directly to low-Cl- water to determine their sensitivities to low-Cl- environment.
The results showed that whole-body Cl- content of three species increased significantly following development. Cl- content in low-Cl- group was not significantly lower than that in normal-Cl- group until H3 in ayu and H5 in tilapia, respectively. However, Cl- content in low-Cl- goldfish was not significantly different from that in normal-Cl- ones from H0 to H5. In the aspect of Cl- influx, larvae of the 3 species acclimated to low-Cl- water had lower Cl- influx rates than did those acclimated to normal-Cl- water after 7 d acclimation.
H3 larvae of tilapia, ayu, and goldfish acclimated to low-Cl- media showed a decrease in Km and no significant change in Jmax compared to those acclimated to normal-Cl- water. During acute low-Cl- challenges, H0 tilapia reacted to decrease Cl- influx initially, and increased to the level in the control group at 24 h after exposure.
It is concluded that whole-body Cl- content of larvae increased significantly following development. The strategies for low-Cl- acclimated larvae to regulate Cl- influx rates may involve in the modulation of transporters to operate their Cl- active uptake. However, the regulation in Cl- influx was not sufficient for recovering the ion loss, indicating that other mechanisms may also involve in the Cl- balance of larvae. Moreover, the present data showed that Cl- uptake efficiency varies among three species. Goldfish possessed a more effective Cl- regulatory capacity than did tilapia and ayu. The differences in the Cl- uptake strategies upon low-Cl- challenge among species may be associated with their habitats.
| Identifer | oai:union.ndltd.org:TW/090NTU00312020 |
| Date | January 2002 |
| Creators | Li-Jung Lin, 林莉蓉 |
| Contributors | , 嚴震東, 黃鵬鵬 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | en_US |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 43 |
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