Thesis

ECOMORPHOLOGICAL ADAPTATION OF JUVENILE FALL-RUN CHINOOK SALMON (Oncorhynchus tshawytscha) TO PERENNIAL AND EPHEMERAL STREAM TYPES

Body shape of juvenile fall-run Chinook salmon (Oncorhynchus tshawytscha) reared in a perennial stream environment were compared to juveniles reared in an ephemeral stream environment. In the Central Valley of California, habitat characteristics differ substantially between these two stream types and therefore present different challenges with respect to water discharge, water temperature, food availability, and habitat complexity. Using multivariate analyses conducted via geometric morphometrics, this study presents morphological differences observed within and between two stream types. As predicted, juvenile Chinook salmon exhibit rearing habitat-specific body shapes. Differences in juvenile Chinook salmon morphology between stream types were primarily associated with expansion of the mid-body region relative to, differences in body length. Specifically, juvenile Chinook salmon that reared in the ephemeral stream expressed increased body depth dominated by dorsal-ventral elongation of the dorsal fin-body insertion points, increased adipose fin-body dorsa-posterior angle, and increased anal fin-body ventral posterior angle. Additionally, eye position and gill opercula-body insertion points were anteriorly shifted in the juvenile body shape of the ephemeral stream. Differences between ephemeral and perennial stream environments likely influence the body shapes observed in this study, and suggest that juvenile Chinook salmon are morphologically flexible and readily adapt to rearing habitat conditions

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