Noninvasive assessment of nitrate‐induced stress in koi Cyprinus carpio L. by faecal cortisol measurement |
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| Authors: | Samuel J Lupica John W Turner Jr |
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| Institution: | Department of Physiology and Pharmacology, College of Medicine, University of Toledo, Toledo, OH, USA |
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| Abstract: | This study determined effects of nitrate (NO3?)‐induced stress on faecal cortisol levels in koi (Cyprinus carpio). NO3? was presented in two formats: (1) bulk increase followed by dilution to assess cortisol response and recovery and (2) bulk increase followed by incremental increases to assess cortisol response limit. Fish were maintained group‐wise in treatment and control aquaria (n=6 per group), and 0.5 g L?1 NO3? (as NaNO3) was added to the water. Faecal samples were collected daily and blood samples were taken pretreatment and 72‐h posttreatment and were assayed for cortisol via ELISA. NO3? increased plasma and faecal cortisol 4.4‐fold and 3.9‐fold respectively. Plasma cortisol was not measured further. After a 74% NO3? decrease by dilution, faecal cortisol decreased to baseline within 24 h, and restimulation by NO3? (1.0 g L?1) elevated faecal cortisol to maximal study levels. In a separate experiment, exposure to 0.4 g L?1 NO3? increased faecal cortisol 6.9‐fold. However, three additional 0.4 g L?1 NO3? increments across 9 days did not further increase cortisol. This study demonstrates that faecal cortisol measurement in fish via an ELISA can be useful as an indicator of NO3?‐induced stress in the aquatic environment. |
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| Keywords: | cortisol fish nitrate stress |
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