Modulation of Calcium Uptake in Tilapia Larvae(Oreochromis mossambicus)

• Main Authors: Yang, Chi-Hwa or Chi-Hua, 楊濟華
• Other Authors: Hwang Pung-Pung
• Format: Others
• Language: zh-TW
• Published: 1997
• Online Access: http://ndltd.ncl.edu.tw/handle/96982003192964156810

碩士 === 國立臺灣大學 === 漁業科學研究所 === 85 === The present work is to study the modulation of calcium uptake in tilapia larvae ( Oreochromis mossambicus ). Changes in the total length, body weight, yolk diameter, cadmium content, calcium content and calcium influx of tilapia larvae during cadmium treatment and detoxification were examined.(1) In low-calcium medium larvae treated with 150 ug l-1 cadmium showed over 70% mortality and a significant inhibition in the development and growth at 96 h during the treatment, while those treated with 150 ug l-1 cadmium in high- calcium water for 96 h had less than 2% mortality and developed and grew normally. Similarity, cadmium caused a significant decrease in the calcium content of the larvae in low-calcium medium but no significant effect in those in high-calcium medium. The larvae in high-calcium medium increased, while those in low-calcium medium maintained a constant amount of accumulated cadmium following the increase of environmental cadmium levels. In low-calcium medium, when compared with the control, the larvae treated with 25-50 ug l-1 cadmium enhanced their calcium influx rates to obtain sufficient calcium from the environment. Those treated with 150 ug l-1 cadmium diminshed their calcium uptake capacity due to the serious abnormaly in development, growth and physiological state. On the other hand, high-calcium media may have supplied sufficient calcium for larvae so that 50-150 ug l-1 cadmium did not develop significant change in the calcium uptake capacity of the larvae.(2) In order to examine regulation of calcium influx, newly-hatched tilapia larvae were exposed to cadmium freshwater ( [Ca2+]=0.2 mM ) and then transferred to cadmium-free freshwater. The cadmium-pretreated larvae revealed a dramatic change in the calcium influx, increasing within 24 h after the transfer and then decreasing to the level of control group. The increase of calcium content was more rapid than that in the control right after the transfer, and then slowed down 24 h later while the calcium content reached 56% of that in the control. These results would suggest that: * The increased calcium uptake in the first 24 h is a compensation for calcium loss caused by cadmium exposure. * The higher calcium influx, however, could not be completely explained by the clearance of inhibitor ( cadmium ) from calcium uptake mechanism. * Cadmium-pretreated tilapia larvae seemed to regulate their calcium uptake capacity efficiently depending upon the calcium content in the body.(3) The hypothesis stated above was further testified by the following experiment. Newly-hatched tilapia larvae were exposed to cadmium freshwater ([Ca2+]=2.0 mM)and then transferred to cadmium-free freshwater ( [Ca2+]=2.0 mM ). Compared with the control, the cadmium-pretreated larvae did not enhance significant change in both calcium influx and calcium content. Obviously, cadmium-pretreated larvae needed not do any compensation in calcium influx. The result would confirm that calcium content in the body, but not the ambient cadmium, is the main factor that affect calcium influx. It is concluded that calcium uptake capacity of tilapia larvae were modulated depending upon environmental calcium levels and/or larval calcium content. Moreover, the modulation will be achieved in only a few days, which is faster than adult fish, and this indicates that the tilapia larvae have efficient ability on adaptating to different environments.