Effect of parent type and temperature on vertebrae number in juvenile cod,Gadus morhua(L.), in Northern Norway

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Abstract
Cod juveniles settling in shallow water and recruiting to coastal cod (CC) stocks have lower vertebrae number than juveniles settling in deep water and recruiting to Northeast Arctic cod (NAC) stock. We investigated whether the differences in vertebrae number in CC and NAC were caused by genetic differences or by exposure to different temperatures during the embryonic period when the vertebrae number is determined. Egg groups from NAC and CC parents (parent groups), and egg groups from CC broodstocks (broodstock groups) were maintained at constant temperature during the egg stage and reared to the juvenile stage before their vertebrae were counted. Data on vertebrae number from year classes of CC and NAC were compared with the experimental results. The vertebrae number of the male parents had a greater influence on the vertebrae number of the offspring than the vertebrae number of the female parents, indicating that the parental effect was a genetic sex linked effect. NAC parents produced offspring with higher vertebrae counts than CC parents. There was an inverse relationship between temperature and vertebrae counts in the broodstock groups, but no correlation between average vertebrae number (AV) and expected temperature during the spawning period in Lofoten for the NAC year classes. Our experiments show that the differences in vertebrae number between coastal cod and Northeast Arctic cod are, at least in part, genetically determined.