Abstract
Tilapia cultured in fresh water were acclimated in sea water with daily increase of $5%_{\circ}$ of salinity and it was completely terminated at the 7th day (0 week). Each three tilapia acclimated were examined weekly based from 0 week to elucidate changes of chloride cells in gill, mineral contents and physical properties in muscle and biochemical characteristics in myofibrils. Chloride cells existed in gills were gradually developed in number and size by acclimation to sea water and became to almost constant state at the third week. Shearing value, compressing strength and content of minerals such as Mg, Na and K in muscle were showed remarkable increase by acclimation to sea water in comparison to those of muscle from tilapia reared in fresh water. Myofibrillar $Mg^{2+}-,\;Ca^{2+}-$ and $K^+(EDTA)-ATPase$ activities of tilapia acclimated in sea water also increased showing significant statistic difference (p<0.01) from those of tilapia reared in fresh water However. thermostability of myofibrils was dropped by acclimation to sea water. The increase of shearing value and compressing strength in the muscle of tilapia by acclimation to sea water would be attributed to the increase of myofibrillar ATPase activities which act to accelerate the decomposition rate of ATP. Therefore, it is suggested that this phenomenon associated with muscle contraction could be brought an improvement of texture of tilapia acclimated in sea water.
담수산 틸라피아를 하루 $5%_{\circ}$씩 해수농도를 높여 1주일에 걸쳐 $32%_{\circ}$ 해수에 순화시켜, 이때를 기준(0주)으로하여 1주일 간격으로 염세포의 발달, 근육의 물성 및 미량원소의 변화와 더불어 근원심유의 ATPase 활성 및 열안정성에 대한 변화를 알아보았다. 아가미의 염세포는 해수순화와 더불어 점진적으로 갯수가 늘어나고 크기가 커져 순화 3주째에 발달이 완료되었다. 근육의 절단 및 압착강도도 해수순화에 따라 현저히 증가하여 근육의 물성변화를 보였으며, 일부 미량원소 (Mg, Na, K)도 뚜렷한 측적을 나타내었다. 근원섬유 ATPase 활성은 해수순화와 더불어 담수산의 것에 비해 유의차를 보이며 증가하였다. 근육중의 미량원소의 증가와도 관련이 있을 것으로 보이는 근원섬유 ATPase 활성증가는 결국 근육중의 ATP 분해를 촉진하여 근수축을 신속히 유도, 근육의 탄력을 증대시킴으로써 식감이 개선되는 것으로 추측되었다. 한편, 근원섬유의 열안정성은 해수순화에 의해 현저히 저하되었다.
(National Fisheries Research and Development Agency)
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