MATERNAL AND SEASONAL DIFFERENCES IN EGG SIZES AND SPAWNING CHARACTERISTICS OF CAPTIVE ATLANTIC COD, GADUS-MORHUA

We analyzed the maternal and seasonal contributions to variation in eg g sizes and spawning characteristics among captive Atlantic cod, Gadus morhua, from the Bay of Fundy, Canada. Spawning occurred from late De cember to mid-June. No seasonal change in egg sizes was apparent among the eggs pooled from all females. At the female level, those that beg an spawning later in the year spawned for a shorter duration and had f ewer batches, but these batches were larger and released at higher fre quencies. Effects due to female (n(f) = 10) and batches-within-female (n(b.f) = 73) accounted for 35 and 26% of the total variance in egg di ameters, respectively. Sizes of eggs from batches early in the spawnin g season were predictive of sizes in later batches from the same femal e. Female size was not related to egg size, but females of higher cond ition had larger eggs. The batch effect was largely due to seasonal de clines in egg sizes of the separate females and was related to female condition. Despite the use of constant temperatures in this study, ava ilable information implicates temperature as a dominant factor contrib uting to seasonal changes in egg sizes in nature.