廣鹽性魚類離子平衛與水平衡之研究

Abstract

前人的研究發現黑鯛(Acanthopagrus schlegeli)與吳郭魚(Oreochromis mossambicus)鰓上 Na + , K+-ATPase活性在淡水與海水中趨勢相反。因此我們假設黑鯛與吳郭魚滲透壓調節機制不同。本實驗以淡水的黑鯛與吳郭魚為研究材料，探討黑鯛和吳郭魚淡水適應的滲透壓調節機制的比較。實驗分成離子平衡、水平衡與 MR 細胞的變化情形。在離子平衡的部分，分別探討黑鯛與吳郭魚體內氯、鈣與鈉離子的含量，氯及鈣離子的吸收；水平衡的部分，探討淡水與海水適應的黑鯛和吳郭魚的喝水速率；MR細胞的觀察部分探討淡水適應的黑鯛和吳郭魚 MR 細胞的形態與數目的變化。 離子平衡的部分，淡水的黑鯛，體組織氯離子的含量顯著的低於淡水的吳郭魚。在氯離子的速率方面，淡水的黑鯛其體內氯離子的流出速率大於流入速率而呈現為淨流出的現象，而淡水的吳郭魚體內氯離子的流入速率大於流出速率而呈現為淨流入的現象，顯示黑鯛和吳郭魚適應淡水的滲透壓調節機制可能不同。淡水的黑鯛，體組織鈣、鈉離子的含量與淡水的吳郭魚並沒有顯著的差異。淡水的黑鯛與吳郭魚其體內的鈣離子流入速率與喝水速率皆沒有顯著差異。MR細胞的觀察結果顯示 ，淡水的黑鯛鰓上 MR 細胞主要的形態是突起型 ，根據前人的報告，突起型MR細胞鰓上 Na + , K+-ATPase活性較高，此一現像是適應低氯環境的補償作用。所以正常淡水氯濃度的環境底下對黑鯛來說是一個低氯的環境，黑鯛對環境氯離子濃度的反應比吳郭魚更敏感，可是淡水黑鯛氯離子的吸收並沒有增加，顯示黑鯛氯離子的吸收機制的效率較差或者黑鯛氯氣離子吸收的機制不同。

The previous study showed that black porgy (Acanthopagrus schlegeli) and tilapia (Oreochromis mossambicus) showed reverse patterns in the gill of Na+,K+-ATPase upon salinity challenges. Hence, we hypothesize that black porgy and tilapia exhibit different mechanisms of osmoregulation. To test the hypothesis, the experiment were focused on the comparisons in ion balance, water balance and morphology of MR cells between balck porgy and tilapia acclimated to fresh water (FW). Whole-body chloride content in FW black porgy is significant lower than that in FW tilapia. However, there is no significant difference in calcium or sodium content between FW black porgy and FW tilapia. The chloride influx in FW black porgy is significantly lower than that in FW tilapia, but no significant difference in the chloride efflux was found between the 2 species. As a result, chloride net flux is negative in FW black porgy but is positive in FW tilapia, suggesting differences between the two species in the chloride uptake mechanism in FW. FW black porgy and FW tilapia have no significant difference in water drinking rate or in calcium influx. The apical openings of gill MR cells in FW black porgy are all wavy-convex type, while shallow-basin and deep-hole types occur in gills of FW tilapia. FW black porgy has more numerous MR cells than does FW tilapia. The more MR cells with wavy-convex apical openings (i.e., larger apical surface area) is associated with the higher gill Na+,K+-ATPase activity in FW black porgy. Taking all together into account, FW black porgy seems to be more sensitive to environmental chloride concentrations than FW tilapia. Black porgy may have to develop more MR cells with larger apical surfaces in order to absorb sufficient chloride from normal FW, but a lower chloride influx suggests a different chloride uptake mechanism with lower efficiency in black porgy comparing with that in tilapia.