SPAWNING ENERGETICS OF ARCTIC COD (BOREOGADUS-SAIDA) IN RELATION TO SEASONAL DEVELOPMENT OF THE OVARY AND PLASMA SEX STEROID-LEVELS

Gonadal development in Arctic cod starts in August in high Arctic Cana da. Male gonads develop at a faster rate than female gonads initially, and reach maximum size about two months prior to females. Under labor atory conditions (at 1.0 degrees C), female Arctic cod became ripe and started to spawn in mid-February, which concurred with field observat ions. Ripe gonad weight increased with body size; mean gonadosomatic i ndex (GSI) of ripe females was 47.7%, and potential fecundity averaged 26 500 eggs. At the time when ripe females started to spawn, some fem ales were still unripe (GSI = 20.2%). Their eggs were not hydrated, an d these fish had significantly higher levels of sex steroids (estradio l, 11-ketotestosterone, and testosterone) in their blood than ripe fis h. Arctic cod are repeat spawners, at least under laboratory condition s, in spite of the large amount of energy allocated to reproduction (3 06 kJ lost from liver and muscle during gonadal development and 125 kJ as eggs during spawning). A high energy investment into reproduction, for a fish that matures at an early age, may be balanced against high predation rates on this species during the open-water season in the C anadian high Arctic.