Enhancing salmon conservation releases through improved brain development and behaviour

Abstract

Captive breeding programmes are based on the practice of taking part of an endangered population to captive environment and releasing the captive-born offspring back to the wild. Despite the vast ecological and economical investment in restoration of endangered animal populations through captive breeding programmes - annually more than 5 billion to salmonid fishes alone - they have been unfortunately unsuccessful. The low success of captive breeding programmes is mainly due to lowered fitness of the released animals and their offspring in the wild. Degradation of many behavioural and other fitness related traits are due to (i) very fast genetic domestication and (ii) habituation to the unnatural rearing environment during ontogeny. This study is the first to examine the relative importance of the effects of genetic domestication and unnatural environment on adaptive behaviour after release to the wild and its underlying neuroanatomic mechanisms. We found that adaptive post-release behaviour in the wild is selected against in captivity and further dumbed by unnatural rearing environment. These negative effects on adaptive behaviour were directly related to decreased brain development. This is the first study showing that using wild parents and a novel naturalized rearing method promoted brain growth. Even more importantly, both in laboratory experiments and in releases to the wild, larger-brained salmon showed better foraging performance. Our findings and methods are directly applicable to increase success of salmon captive breeding programmes, as we used real production scale rearing facility and fish densities.