Spawning-related mortality in captive Atlantic cod (Gadus morhua L.)

Abstract

Two year-classes of Atlantic cod were reared in indoor tanks from November 2002 to November 2004. The average annual mortality was 21% and 36% for males and females respectively. The highest monthly mortality rates in females were observed around and during the spawning periods from March to July, maximally 7% and 20% for year-class 2001 and 18% and 34% for year-class 2000. The mortality in males was less dependent on season, reaching a maximum of 7% and 5% month−1 for year-class 2001 and 2000 respectively. The maximum mortality during spawning increased with age from: 7%, 19% and 34% per month for 2-, 3- and 4-year-old females respectively. The average gonadosomatic indices in 3- and 4-year-old mature females that died during the spawning periods were 22% and 26% respectively and most of them were spawning when they died. The results suggest that egg-retention may have been the main cause of death in females during spawning.