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The survivorships and growth rates ofPlanorbarius corneus andPlanorbis planorbis were measured during the whole life spanof the snails at constant temperatures of 5, 10, 15, 20 and25°C. Life expectancy tables were constructed. The maximumlongevities for P. corneus (231 weeks) and P. planorbis (175weeks) occurred at 15°C and 10°C respectively. The extremetemperatures were particularly unfavourable. Snail growth which was expressed logarithmically was most sensitiveto temperature during the exponential stage. However, if weconsider a given species duringjts entire life span, there wereno significant differences between temperature groups whichwere in order of decreasing suitability: P. corneus: 25, 20 and 15°C; 10°C; 5°C; P.planorbis: 20 and 15°C; 25 and 10°C; 5°C. Using the growth constants from the Von Berta-lanffy's modeladjusted to give a gaussian curve, it was calculated that theoptimum temperatures for the growth of P. planorbis and P. corneuswere 19 and 20.5°C respectively. A mathematical model basedon spline functions makes it possible to predict the growthof snails over a wide range of temperatures. (Received 2 June 1993; accepted 18 November 1993) 相似文献
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