Effect of experience on feeding behaviour: Captive-bred cod adapt more slowly to prey encountered in a novel manner than do wild cod

When captive-bred cod were released for sea ranching in Masfjorden of western Norway, it was evident from field samples that these fish had a different diet and higher mortality rate than wild cod at least the first three days after release. Moreover, these captive-bred cod were released into the natural habitat in a number that largely exceeded that of wild cod. Despite of this their abundance reduced dramatically during the spring as one year old and just six months after the releases. In this paper I study experimentally if groups of captive-bred cod have a different feeding behaviour than wild cod and if they adapt differently to prey. Results show that captive-bred cod adapted more slowly than wild to prey that were encountered sequentially, which represents a novel feeding context compared to hatcheries where fish usually obtain many prey simultaneously although both wild and captive-bred had taken these prey earlier when many were given. Wild cod had higher feeding rates that increased rapidly with treatment day. Captive-bred cod refused to take prey the first five treatment days, spent more time on each prey item and obtained the lowest growth rates.  A positive effect of group size on feeding skills was found for captive-bred cod but not for wild, but even so, their growth rate was lower than that of wild. I discuss these results in the light of the different experience the fish had gained prior to the experiments and possible consequences for sea ranching.