Time course of gametogenesis in Northwest Atlantic cod (Gadus morhua)

Atlantic cod (Gadus morhua) cod are iteroparous (repeat spawners) with diverse patterns of gamete development. Studies of reproduction of wild cod have sometimes been complicated by the presence of spring and fall spawners. By combining data from wild and captive fish from known locations, the present study clarifies the time course of gametogenesis culminating in spawning. There is evidence that females may have an adolescent phase, pausing in stages of oogenesis more advanced than that of immature juveniles. Data also suggest that both male and female adults can omit a spawning; this interruption, still under study, may be a normal facet of cod reproduction in response to low levels of feeding for individual fish. Spermatogenesis seems subject to delays in its initial phases, with fish showing considerable variation in stages attained. Individual males can achieve a higher gonadosomatic index than females, which is unusual. Both male and female cod show large variations in gonadosomatic index for wild reproductive fish, which must mean large variations in fecundity, and may mean that many fish are not reproducing at full potential.