KIHSLINGER, R./L.; NEVITT, G./A.; Univ. of California, Davis: The early rearing environment produces variation in the size of brain subdivisions in steelhead trout (Oncorhynchus mykiss).

The early rearing environment plays a critical role in the development and expression of phenotype. Environmental effects on development may be exaggerated in captive rearing or hatchery situations where the rearing environment is dramatically different from the wild environment. Hatcheries consistently produce fish that are behaviorally and physiologically different from their wild counterparts. In addition, the relative brain size of wild salmon is larger than that of fish reared in a hatchery. The specific components of the environment that may influence this neuroanatomical difference, however, are not known. This study examined the role of the structural environment during the alevin life-stage (recently hatched juvenile) on the neural development of steelhead trout (Onchorhynchus mykiss). The alevin life-stage is a stage during development when fish are likely to be influenced by their environment. The structural components of this environment are known to alter growth rates and other physiological characteristics during this life stage. To assess the affects of the structural environment on neural development, fish were reared in three control and three structurally enriched tanks (Mexican Beach Pebble, 10 cm in diameter). Fish reared in environments that contained structure were significantly heavier (H(1, N = 180) = 30.65, p < 0.001) and longer (H(1, N = 180) = 15.57694, p < 0.001) at emergence than fish reared without structure. Total brain volumes were not different between treatments suggesting that the brain grew at the same rate in both rearing environments. However, preliminary evidence suggests that subdivisions within the brain grew at different rates in fish reared in structurally enriched compared to control environments.