Variations cycliques de la tolérance à un choc thermique froid appliqué au cours de la segmentation de l'embryon de la carpe commune (Cyprinus carpio L.)

Common carp (Cyprinus carpio L.) eggs incubated at 16 °C were plunged into melting ice (0.3 °C) during the first cleavage stages with the aim of determining their sensitivity to cold shock. The effects of the shocks were estimated by the survival rates of embryos on days 2 and 6 of prehatching. After a brief cold shock (10 min), embryos showed a regular succession of sensitive and tolerant phases. Survival rates indicated that there were 9 sensitive phases at the caudal bug stage and 12 at the prehatching stage. This rhythm corresponded to the periodicity of cell division in the rapid cleavage stage. The embryos became progressively more tolerant to cold shock. With an increase in the duration of the cold shock (50 min), an assymetrical widening of the mortality peaks was observed. The progressive acquisition of tolerance to cold shock in carp embryos might be related to a desynchronisation and a slowing down of the cell cycles during the early cleavage stages.