Variation in annual egg production in individual captive Atlantic cod (<i>Gadus morhua</i>)

Abstract

Variability in the annual egg production of hatchery-reared Atlantic cod (Gadus morhua) was determined under&#13;\nstable experimental conditions. Egg size increased with fish age as an approximate step function. Comparing first- and&#13;\nsecond-time spawners, the variance in egg dry weight was 32% within individuals (i.e., the seasonal effect, the cod being a&#13;\nmultiple-batch spawner), 55% between years, and 12% between individuals. In several repeat spawners, the curvature of the&#13;\nseasonal egg size curves showed little difference between years. The seasonal decrease in egg size was typically smaller in&#13;\nrecruit spawners than in repeat spawners. There was no empirical evidence to suggest that environmental temperature&#13;\nregulates seasonal variations in egg size. The extent of egg swelling (i.e., the egg dry weight/diameter ratio) indicated a&#13;\nstrong genetic component. Investment in ovarian growth was influenced by previous allocations as exemplified by annual,&#13;\nsinusoidal fecundity oscillations. Larger fish showed significantly longer spawning periods. The combined influence of&#13;\nmaternal factors and the annual temperature variations noticed in the field during early stages suggests that larger larvae at&#13;\nthe onset of feeding are more likely to survive.