Physiological Changes with Age in Fish 197 



fecundity to length is not a simple one and can be broken 

 down into three parts, possibly a sigmoid curve. Eschmeyer 

 (1950, 1955) has described a sigmoid fecundity /length re- 

 lationship in the walleye {Stizostedion vitreum) and lake trout. 

 The correlation of a decrease in the rate of egg production 

 with age was regarded by Katz and Erickson as a criterion of 

 ageing in the herring. 



A ballot on whether or not the strain of reproduction in the 

 Atlantic and Pacific species of herrings upsets the homeostatic 

 mechanism to the point where the fish dies as a direct or 

 indirect effect of its reproductive efforts yields three votes 

 affirmative, one vote negative. The affirmative votes should 

 be scrutinized carefully, however, because none of them were 

 cast after having taken individual variation into account. 



Salmon. Some interesting information has been accumu- 

 lated which indicates that age influences egg production in two 

 species of salmon. The Atlantic salmon (Salmo solar) spawns 

 in rivers after spending either two or three years in the sea and 

 some may spawn more than once. Belding (1940) studied the 

 fecundity of this species from the Gulf of St. Lawrence and 

 learned that the youngest spawners, those which had lived 

 two years in the sea, produced a greater number of eggs in 

 relation to their weight (834 eggs per lb.) than either three- 

 year sea-life individuals (723 eggs per lb.) or those which had 

 previously spawned (738 eggs per lb.). In actual numbers the 

 two-year salmon produced 8,850 eggs per female and the 

 three-year salmon produced about 14,000. He attributed this 

 decline in relative egg production in part to the fact that large 

 salmon usually have larger eggs than small salmon, but he did 

 not discount age as a factor influencing egg production. 



Rounsefell (1957) has made a more detailed study of fecund- 

 ity of the sockeye salmon {Oncorhynchus nerka) in the Karluk 

 River, Alaska. In this part of the world the young sockeye 

 spend either three or four years in freshwater lakes before 

 migrating to the sea and remain there either two or three 

 years before returning to freshwater streams to spawn. 



