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Changes in otolith morphology of juvenile chinook salmon (Onchorhynchus tshawytscha) in different hatchery rearing conditions

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  • The decline of the Chinook Salmon has been a mystery of recent years due to their decline. It has been speculated that wild origin salmon have more vigor and survivability than hatchery reared fish. This is thought to be due to rearing conditions, possibly affecting sensory organ development. The sensory structure of interest is the otolith, a calcium carbonate structure within the inner ear. All teleost fish contain otoliths, structures that reside in the inner ear that aid in balance, orientation, and linear acceleration. There are three pairs of otoliths in a fish’ semicircular canals, with the Sagittal pair being the largest and most variable in morphology. These structures grow seasonal rings and are not subject to reabsorption, so they provide a permanent life history record of the individual. To assess these conditions, the otoliths of the fish can be examined to reveal age estimates as well as environmental factors in which it was reared. Assessing the final shape of the otolith after extraction can help us understand how environmental factors influence the shape of the otolith. This study branches from a previous study done on the otolith asymmetry between wild adult chinook salmon and hatchery origin, to see if there are any differences in their end shape. In this study, juvenile salmon were used to assess a similar goal, only at a different stage of development. Assessing the otolith shape as juveniles can help us further understand the developmental hindrances. These developmental hindrances would show as variations in otolith shape amongst the experimental group. In these experimental groups, juvenile salmon were subjected to a conventional hatchery setting, while another group was subjected to a naturalized “wild” environment. The goal of this study is to determine if there is a morphological difference between otoliths extracted from fish in a “wild” mimicked environment, versus a conventional hatchery rearing environment.
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