Résistance de l'œuf de carpe commune (Cyprinus carpio L. Cyprinidae) à des chocs thermiques chauds ou froids

The resistance of common carp (Cyprinus carpio L.) eggs to hot and cold shock has been studied by measuring the survival rate during the course of an incubation at a constant temperature of 20 °C. When incubation was pursued in oxygen-saturated conditions, a 1-h-long thermal shock which occurred during the synchronous segmentation stage had no effect within the temperature range of 8–28 °C. At gastrula stage, this interval reached 0.3 °C and at the end of epiboly it reached 36 °C. With hypoxic incubation conditions, a 1-h postepibolic shock had no effect within the range of 1–36 °C. On the contrary, a 12 °C (or less) preblastulean cold shock or a 30 °C (or more) pregastrulean hot shock induced a significant loss of further resistance to hypoxy. An overoxygenation during the shock did not increase the embryonic resistance. During the synchronous segmentation, the sensitivity to cold shock varied occasionally, possibly in relation with the mitotic cycle. Sensitivity to thermal shock also depended on the gametes' fertility. The resistance to thermic shock was compared with the thermic profiles that are described to be optimum in laboratory conditions at constant temperature, or in natural conditions of development. Hypoxy or hyperoxy cannot be the determining factor in thermic-shock effects on carp eggs: several hypotheses were reviewed to explain the acquisition of an increasing resistance to the variation of the environmental temperature.