Assessment of female gamete quality in the Pacific oyster Crassostrea gigas

The possible relationship between certain oocyte and embryo characteristics and larvae viability was investigated with reference to the following aspe cts: (1) morphological - oocyte diameter and shape; (2) cytological - overa ll ultrastructure and membrane integrity; (3) biochemical - content of lipi ds, proteins and carbohydrates; and (4) physiological - respiration. The ra te of survival and incidence of abnormality were estimated 24h after fertil ization, The first results showed that 80-90% of oocytes were cytologically viable before fertilization, Eighty to 90% of oocytes are apparently viabl e before fertilization on the basis of staining with Trypan blue, but this parameter shows little correlation with larval viability. However, Trypan b lue staining is of value in allowing the recognition of oocytes with damage d membranes, Respiration was measured for unfertilized oocytes 5 min after stripping, after 6 h, and for 3-h embryos. Positive correlations were found between the O-2-consumption of embryos and both the rate of fertilization and the hatching rate of 24-h larvae, In contrast, no correlation was found between hatching parameters and the O-2-consumption of unfertilized oocyte s. These results suggest that embryos possess quality indicators, relating to metabolic characteristics, which can be quantified more easily than thos e of oocytes.