Effect of low water temperature exposure in the winter in suppressing the onset of the reddening adductor disease in the Japanese pearl oyster Pinctada fucata martensii
2008
Iwanaga, S.(Nagasaki-ken. Inst. of Fisheries (Japan)) | Suzuki, M. | Mori, Y. | Tsukahara, J. | Hosokawa, H.
In order to find out a effect of low water temperature treatment in reducing the reddening adductor disease caused mortality of the Japanese pearl oyster Pinctada fucata martensii in Nagasaki Prefecture, mortality and physiological traits were compared each month for one year between the different groups of oysters kept in various pearl farms where temperatures were below 13degC during winter, whereas control shells were kept in a warmer area. As an indicator of low temperature burden, the low-water-temperature index [LTIsub(13)=Sigma(13-Tn), Tn13] was calculated from the water temperature measured each day at 10 o'clock (am) for each group of oyster. As compared to control, the 100 degree-day group showed lower mortality, lower a-value (value obtained from the spectrophotometer and used as a color indicator for the reddening adductor), slower gonad maturation, higher glycogen content in the adductor muscle and higher phyto-pigment content in the digestive diverticula after wintering particularly from spring to autumn when the reddening adductor disease progressed. The high survival rate in the 100 degree-day group at the end of experiment may be attributed to the delayed onset of the reddening adductor disease which was a result of higher glycogen content, delayed maturation and increased food intake of the oysters.
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