This study demonstrates that vegetable shortening and cocoa butter are two effective vehicles for intraperitoneal cortisol implants in juvenile teleosts, specifically brown trout Salmo trutta, residing in north temperate freshwater environments. Each vehicle showed a different pattern of cortisol elevation. Vegetable shortening was found to be a more suitable vehicle for long-term cortisol elevation [elevated at 3, 6 and 9days post treatment (dpt)], while cocoa butter may be better suited for short-term cortisol elevation (only elevated at 3 dpt). Additionally, plasma cortisol levels were higher with cortisol-vegetable shortening than with cortisol-cocoa butter implants. Plasma glucose levels were elevated 6 and 9 dpt for fishes injected with cortisol-vegetable shortening, but did not change relative to controls and shams in cortisol-cocoa butter fishes. In conclusion, vegetable shortening and cocoa butter are both viable techniques for cortisol manipulation in fishes in temperate climates, providing researchers with different options depending on study objectives.

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Keywords Cocoa butter, Cortisol implants, Salmo trutta, Teleost, Vegetable shortening
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Journal Journal of Fish Biology
Birnie-Gauvin, K. (K.), Peiman, K.S. (K. S.), Larsen, M.H. (M. H.), Aarestrup, K. (K.), Gilmour, K.M. (K. M.), & Cooke, S.J. (2017). Comparison of vegetable shortening and cocoa butter as vehicles for cortisol manipulation in Salmo trutta. Journal of Fish Biology. doi:10.1111/jfb.13513