Cod egg characteristics and viability in relation to low temperature and maternal nutritional condition

Abstract

In 1995 and 1996, groups of female cod ( Gadus morhua ) of varying nutritional condition and maturing at different temperatures were used to investigate relationships between female condition, egg production, egg characteristics, and viability. Over the two years, egg samples from every batch spawned by 34 females were analyzed for egg diameter, dry mass, and energy content. In addition, 51 egg batches from 24 females (ca. 2 egg batches female ⁻¹ yr ⁻¹ ) were used to monitor development rate and hatching success. The weighted mean egg dry mass was positively correlated (p<0.05) to the females' pre-spawning condition in 1996. In 1995 this positive correlation was not observed for females at ∼2°C during maturation. For both years, the decline in the mean egg dry mass per batch throughout spawning was correlated (p<0.05) with the females' post-spawning energy reserves. However, no trend in the total egg dry mass per batch during the sequence of spawning was observed. Thus, the total energy investment per batch remained stable throughout spawning and was not influenced by the depletion of the females' energy reserves. In 1996, high hatching successes were observed only for egg batches from females in high pre-spawning condition. However, egg size and dry mass showed no correlation with survival rate or hatching success in either year.