KIHSLINGER, Rebecca L*; NEVITT, Gabrielle A; Univ. of California, Davis: Sending fish to preschool: Early enrichment affects brain and behavioral phenotype in salmon.

It is well established that rearing environment plays a critical role in the development of phenotype. This role may be more pronounced in organisms that experience a dramatic change in environmental conditions, either from anthropogenic alteration of habitat or artificial rearing. Understanding the basic mechanisms driving phenotypic plasticity is thus critical when developing conservation strategies for imperiled species. This may be especially important when animals are reared in captive rearing situations where the rearing environment is dramatically different from the wild environment. Our study examined how structural enrichment influences the phenotypic development of genetically similar strains of steelhead salmon (Onchorhynchus mykiss). Results suggest that early exposure (i.e., before yolk absorption) to structural enrichment influences both the neural and behavioral development of young fish. Fish reared with structure during early rearing are larger, emerge (become free swimming fry) later and are less likely to receive aggressive attacks as juvenile fish. Further, one brain subdivision, the cerebellum, was significantly larger in fish reared with structural enrichment than in those reared in conventional hatchery environments. This developmental variation may contribute to the differences we observe among hatchery and wild strains of salmonids. The impacts that captive rearing practices have on fish once they are released into the wild are frequently overlooked since management must often focus on the protection of specific genetic stocks than on fine-tuning ways to maintain phenotypic variation in captivity. This study is among the first to provide an integrative framework for investigating how enrichment contributes to variation in phenotypes, and suggests a need to look beyond genetics in preserving wild strains of fish in captivity.