The effects of environmental pH during fertilization in carp eggs were studied by measuring the percentage of prehatching embryonic survival. These effects, which may be delayed beyond epiboly, were the same when the treatments lasted 15 and 30 min after insemination, and they were not modified either by the addition of a physiological salt solution to the medium or by exposure of the eggs for 10 s before insemination. Among the six types of buffer used, phosphate buffers were particularly toxic which may indicate the role played by calcium during fertilization. Normal fertilization requires that the osmolarity of the medium be lower than or equal to 200 mosmol/kg. Beyond the limits of favorable pH values (7.2 and 9.6), egg tolerance decreased less rapidly in a weakly buffered medium than in a strongly buffered one. In such a medium, there was no resistance at pH 6.2 or 9.9.
Summary. Physiological tolerance of carp (Cyprinus carpio L.) eggs in response to acid shock during activation or early cleavage.The tolerance of common carp eggs to a short acid shock (10-30 min) was studied by plunging the eggs in a strongly buffered acid solution during their activation or cleavage.Egg tolerance increased during activation ; its cyclic pattern then followed the rhythm of segmentation division. Egg sensitivity depended on shock duration, pH value and buffering strength of the acid solution. Egg tolerance was very high at the end of epiboly. During the first cycle of tolerance variation, an increase in shock strength (low pH) or duration caused asymmetrical widening of the cyclic sensitivity peaks.The tolerance cycle did not appear to fluctuate in all of the trials. The results have been interpreted in relation to some processes involved in egg activation (water inflow through the shell, variation in membrane permeability, calcium wave within the cytoplasm) or to the existence of an acid-sensitive phase in the blastomere cell cycle during synchronous cleavage.Introduction.
Summary. Prehatching embryo survival of 9 freshwater fish eggs after a pH shock during fertilization or early stages of development.The tolerance of freshwater fish eggs to a pH shock was studied by plunging the eggs for 30 min into highly buffered acid or alkaline solutions and by measuring the survival rates at the eyed embryo stage. The study was made on eggs from 9 species : common carp, roach, crucian carp, rainbow trout, brown trout, houting, artic char, pike and perch subjected to acid or alkaline shocks either during fertilization or after activation of the egg.During the life cycle of fresh water fish, the fertilization stage represented a period of high sensitivity to acid shocks for all 9 species : a pH value of 5 was lethal under our experimental conditions. Cyprinids and rainbow trouts seemed to be the most sensitive to an acid pH. During egg activation, a large increase in the tolerance of the egg to the pH shock was observed.Introduction.
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