Oocyte Recruitment in First-Time Spawning Atlantic Cod (Gadus morhua) in Relation to Feeding Regime

Adolescent (10-mo-old, ≈165 g) Atlantic cod (Gadus morhua) hatched and reared in the laboratory were transferred to three different feeding regimes (groups) for a full year, high–high (HH), low–high (LH), or high–low (HL), switching the ration size after 5 mo in July (i.e., before vitellogenesis). Subsequent analysis of fecundity before the first spawning season revealed that adolescent body weight was most important for fecundity followed by growth rate in the autumn, while growth rate in the spring contributed insignificantly. There existed a significant positive correlation between individual, starting (adolescent), and final body weight. All groups were characterized by high individual variability in both fecundity and oocyte development, suggesting strong genetic influences. The groups showed different final mean body weights (HH: 1265 g, LH: 1199 g, and HL: 886 g) but, unexpectedly, the same mean relative fecundities (number of oocytes per gram of ovary-free fish) (≈1200). The study on oocyte sizes provided evidence that HH fish will commence spawning earliest in the year followed by LH fish and then HL fish.