Spawning Success of Farmed Atlantic Cod (Gadus morhua): Effects of Photoperiod on Gonad Development in Sea Cages in Eastern Canada IES CM 2009

No abstracts are to be cited without prior reference to the author.

The use of extended daylength to suppress sexual maturation of Atlantic salmon (Salmo salar) in sea cages has been successfully adopted by fish farmers. The same methods when applied to Atlantic cod (Gadus morhua) however, have been disappointing as gonadal development of cod in sea cages exposed to extended daylength is seasonally delayed but not arrested. Results of a set of photoperiod trials using 20 h and 24 h light in sea cages indicated that between 87-100% of fish achieved sexual maturation. The use of lights did however delay sexual maturation such that females were gravid for several months through summer. Grower diets currently used in Atlantic Canada have led to enlarged livers and this may also have played a role in disrupting normal gonadal development and affected gamete quality. Hepatosomatic indices were also well above those of wild cod. In Canada, the fate of drifting eggs from sea cages has not been evaluated. We discuss some of the biological and environmental conditions in the Bay of Fundy near cod cage sites and make inferences about the potential survivorship of embryo “escapes’. The extent of Atlantic cod farming in Canada is in a preliminary phase with limited concentration in the Bay of Fundy and coastal Newfoundland with no escaped juvenile or adult cod reported to date.