<論文>低水温下におけるアサリの低塩分耐性に関する実験的検討

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A mass mortality of the short-necked clam Ruditapes philippinarum (Adams & Reeve) occurred in Lake Saroma, northeastern Hokkaido, in March 1997 when sea-ice melting began and fresh water discharged. The clams are reported to inhabit the shore of this lake in water of water temperature ranging -1.5〜-0.2℃, and salinity of 7.1〜31.4 psu in winter. To find out the possible cause of mass mortality, we conducted experiments on the effects of salinity at low temperatures with assumption that the low saline water derived from melted ice weakens the clams. The salinity tolerance experiment was carried out in laboratory on the short-necked clams (31.6〜38.0mm SL), which were collected from Lake Saroma in October 1997. Oxygen consumption rate was measured as an indicator for the tolerance. Five individuals of the clams were placed in a closed bottle of 32psu saline water without sand on the bottom for three temperatures, 0,5 and 10℃. The dissolved oxygen was monitored for every 30 minutes over 3 hours, by using a DO meter. Salinity tolerance of the clams was tested on 18 different combinations of temperature and salinity. The tested temperatures were 0,2 and 5℃ and salinity were 0,4,8,16,24 and 32psu, respectively. Control bottle condition was maintained as 20℃ and 32psu containing sand as substratum. After submerged in each experimental bottle from 1 to 20 days, the clams were then placed in the control bottle, and the survived number of individuals was counted after 24 hours. The relation between the oxygen consumption rate (y : mg O_2/hr/g of molluscous part) and water temperature (x : ℃) was expressed by an empirical equation : y=0.0209x+0.014,(0℃≦x≦10℃) , indicating the oxygen consumption rate is low at lowered temperature. The 50 % lethal time of the clam to the combined effects of low salinity (0〜8 psu) and temperature (0〜5℃) was observed after 17〜20 days without particular tendency, whereas the lethal rate remained low even after 20 days when salinity was high in the range of 24〜32psu at all the temperatures tested. We conclude that the short-necked clams will encounter the harmful condition when low salinity condition lasts longer with low temperatures.
北海道東海大学の論文
2002-03-25

<論文>低水温下におけるアサリの低塩分耐性に関する実験的検討

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