Biochemical changes associated with overripening of the eggs of rainbow trout Salmo gairdneri Richardson

Abstract

This study of the biochemical composition of mature unfertilised eggs of rainbow trout was undertaken to investigate normal intraspecific variation in egg composition between parent females, and to describe the biochemical changes which occur after ovulation during overripening in the parental abdominal cavity. The following aspects of egg composition were measured: wet and dry weight, chorion weight, free and bound lipid, protein phosphorus, lipid phosphorus, precipitable protein, calcium, and iron. All these were determined on single eggs, and six eggs were examined from each female. Ripe eggs, defined as those stripped within 3 days of ovulation, were obtained from 7 females. Overripe eggs, defined as those stripped 30 or more days after ovulation were obtained from 8 females. Results were expressed in absolute terms (mg or μg of component per egg) and relative terms (percentage of egg dry weight). In ripe eggs, there was significant variation between females in all these aspects of egg composition when expressed absolutely, and in all except lipid phosphorus when expressed relatively. In overripe eggs, there was significant variation in all these aspects between females when egg composition was expressed either absolutely or relatively. Comparison of ripe and overripe eggs showed that overripening was accompanied by the following significant changes expressed absolutely: increase in water content, free lipid, iron, calcium; decrease in bound lipid, precipitable protein, protein phosphorus, lipid phosphorus, total lipid and chorion weight; when expressed relatively there were increases in water content, free lipid, iron, calcium, total lipid and chorion weight, and decreases in bound lipid, precipitable protein, protein phosphorus and lipid phosphorus.