Batches of eggs (1 batch/female) from 17 rainbow trout in their 1st spawning season were stripped and reared separately, and the percentage which hatched and the percentage which reached the stage of 1st feeding were determined. The fertilized egg batches were analyzed for egg wet weight, egg dry weight, chorion weight and levels in the eggs of free, bound and total lipid, precipitable protein, protein P, lipid P, Ca and Fe. All determinations were made on single eggs, and 6 eggs from each batch were analyzed for each variable. Results were expressed in absolute terms (as weight of component per egg) and as percentage of egg dry weight. Highly significant variations in all these aspects of egg composition occurred between parent females. There was no significant correlation between the percentage of the original number of eggs which hatched and any 1 aspect of egg composition, except for a weak positive correlation (P < 0.05) with the percentage of protein P in the eggs. There was no significant correlation between the percentage of the original number of eggs which reached 1st feeding and any 1 aspect of egg composition except for weak positive correlations (P < 0.05) with egg wet weight and with the absolute level and the percentage of protein P in the egg. There was significant positive correlation (P < 0.05) between the percentage of hatched eggs (alevins) surviving to 1st feeding and each of the following: egg wet weight, egg dry weight and absolute levels in the egg of bound lipid, precipitable protein and protein P. Egg batches with higher hatching percentage (> 50%) differed significantly from those with zero hatching percentage in having (in absolute terms) higher egg weight, chorion weight, protein P (all P < 0.001), egg dry weight, bound lipid and precipitable protein (all P < 0.01) and (percentages) higher chorion weight (P < 0.05) and protein P (P < 0.001) and lower free and total lipid (P < 0.01) and Fe (P < 0.05). In a separate experiment to investigate the effects of allowing the eggs to be retained by the female within the abdominal cavity for increasing periods of time after ovulation, eggs were obtained from 3 females on 3 or 4 successive occasions 2-11 days apart. Althouth the above aspects of egg composition remained almost constant when the eggs were held in the female for up to 18 days after ovulation, the hatching percentage declined sharply within this period, in 2 females falling from > 90% to near zero. The time of stripping of the eggs in relation to the date of ovulation was a more significant determinant of egg quality than any chemical or physical aspect of egg composition investigated.
