| Summary: | The development of cod eggs from various parent fishes was studied. Fertilization success, and proportion of normally developing embryos and larvae varied according to the quality of the eggs. Eggs from poor quality cultures had a significant increase in yolk osmolarity during the first 24 h after fertilization, and maintained higher osmotic values throughout the development than eggs of good quality. Fertilization in different salinities affected yolk osmolarity for all egg cultures, whereas a transfer to different salinities 24 h after fertilization did not. The chorion of eggs from good quality cultures was stronger than that from poor cultures. Heavy infection weakened the chorion. Cod eggs collected from the plankton were compared with eggs incubated in the laboratory. Chorion strength was similar to that of good quality eggs, and varied greatly in both groups. The percentage of morphologically abnormal cod eggs from the plankton samples were as high as 20 % when early developmental stages were predominant, but decreased to about 5 % when embryos at a more advanced stage were more common. Chromosome studies of early embryos from good egg cultures revealed few abnormal mitoses. High percentages of abnormal mitoses were often found in bad laboratory cultures, even though the early embryos appeared normal. A surprisingly large number of abnormal mitoses was also found in normal looking embryos from the plankton samples.
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