Photoperiod manipulation and growth of Atlantic cod (Gadhus morhua)

Atlantic cod (Gadus morhua) placed under 24 hour illumination (LL) from 15 months post hatch (MPH), did not spawn at 2 years and only 7.2% were found to be spawning at 3 years. Ultrasound scanning however showed some gonad development from 22-28 MPH in the LL treated group. This data shows that cod reared in enclosed tanks receiving LL from 15 MPH do not spawn at two years, however, they do go through some gonadal development. Cod placed under LL between 6-18 MPH. showed that in order to prevent spawning at 24 MPH, LL must be applied at or before 15 MPH. and after such time not be returned to a SNP. © 2004 Kluwer Academic Publishers.