吳郭魚（Oreochromis mossambicus) 仔魚期鈣離子平衡之研究

Abstract

鈣離子在仔魚發育扮演重要的角色，是生長之所需。本論文以吳郭魚仔魚在不同鈣離子濃度下探討，不同處理時間，以及不同的發育階段，鈣離子吸收機制的調節表現。 當仔魚在鈣離子濃度 0.2 mM人工水中處理時，鈣離子吸收速率在孵化後三天上升最高，配合此時期鰓的增生及功能逐漸健全，可見仔魚鰓之發育與鈣離子吸收速率增加有相當密切的關係。另外，將孵化後不同時期之吳郭魚仔魚置於低鈣環境中發現，在孵化後第三天對於低鈣環境最為敏感。推測在孵化後三天是吳郭魚仔魚大量吸收鈣而且對外界刺激最敏感的時期。 將孵化前24小時之吳郭魚受精卵以三種鈣離子濃度(高鈣[Ca2+]=2 mM,，中鈣[Ca2+]=0.2 mM，低鈣[Ca2+]=0.02 mM）處理，並在孵化後於原來處理之濃度測量鈣離子流入速率（calcium influx)，低鈣組在處理初期鈣離子流入速率較高鈣組低，但在處理後期鈣離子流入率明顯上升，至於鈣含量則明顯降低，顯示以低鈣環境處理後，仔魚離子吸收能力增加是為了補償鈣含量之降低。 長期處理低鈣環境之仔魚，在處理初期孵化後24小時就已經具有調節鈣離子的能力，並隨著處理時間越長，調節能力更加上升。 經由不同抗體檢視，孵化後三天及七天之吳郭魚仔魚鰓具有類似鈣離子幫浦及鈣離子結合蛋白 calbindin-D28k之表現，孵化後零天及三天之仔魚卵黃膜也都可見到類似這些蛋白質的表現。 經由上述可知，孵化後仔魚之成長，在發育初期已經具備調節鈣離子吸收機制之能力，且隨孵化後時間增加而此能力也增加。孵化後三天是吳郭魚仔魚對外界最為敏感的時期。鈣離子幫浦及鈣離子結合蛋白 calbindin-D28k 可能參與仔魚鈣離子吸收的機制。

Calcium ion plays an important role for larvae development. The present study, using different calcium concentrations as environmental factors, investigated the calcium balance mechanism in developing tilapia larvae. The abilities to modulate calcium influx in larvae varied with different acclimation periods and developmental stages. In the artificial freshwater with 0.2 mM [Ca2+], tilapia larva showed the highest calcium influx rate 3 d after hatching, and this was associated with the proliferation of gills which occurred at the same time. Among different stages, 3-d-old larvae showed the highest degree of decrease in calcium influx and in calcium content upon transfer to low-calcium medium These results suggest that 3 d after hatching is the most sensitive to environmental changes. Tilapia larva was acclimated at different calcium concentration including, high calcium ([Ca2+]=2 mM), normal calcium ([Ca2+]=0.2 mM), and low calcium ([Ca2+]=0.02 mM). Calcium influx in low-calcium larvae was lower than that in high-calcium larvae during 24-96 h after hatching, but the former turned out to be higher than the latter 120 h after hatching. The calcium content in low-calcium larvae was lower than that in high-calcium larvae throughout whole experiment. These results suggest that increasing calcium influx is a compensation for decreased calcium content in the larvae adapted to low-calcium environment. Moreover, this adaptation is developed as early as 24 h after hatching, and is dose (environmental calcium concentration) related. Using Western blotting both Ca2+-ATPase-like and calbindin-D28k-like were found to express in gills and yolk-sac epithelia of tilapia larvae. 0-7 d after hatching, suggesting these transport proteins are involved in the calcium balance mechanism of developing larvae.