Nitrate Toxicity to Common Carp Measured Noninvasively by Novel Enzyme-linked Immunosorbent Assay for Cortisol
Abstract (Summary)Measurement of cortisol in fish fecal casts, in both aquaculture and natural settings, is a potentially valuable tool as it is both noninvasive and highly correlated to more commonly invasive methods, such as plasma monitoring. Performance of the cortisol ELISA developed in this study was validated by comparison to high performance liquid chromatography (HPLC), which has been used for measuring free glucocorticoids and glucocorticoid metabolites in feces of numerous mammalian species and has recently been incorporated into studies of fish physiology and behavior. Tests for parallelism and extraction efficiency showed that the ELISA and HPLC resulted in almost identical values. This is the first report of use of an ELISA for measurement of cortisol in fish feces, as RIA and HPLC are the most commonly used methods. The study has also shown that fish cortisol can be measured in fecal material by ELISA and this assay exhibits equal reliability and much greater efficiency and sensitivity than HPLC. From both per-sample assay time and personnel cost perspectives, the ELISA is more practical and less expensive than HPLC analysis, showing that this cortisol ELISA has high potential as a sensitive, reliable and cost-effective tool for noninvasive stress assessment in fishes. In the second part of the study, elevated NO3- was shown to be a significant stressor for koi as evidenced by increased fecal cortisol, loss of appetite, color change, hyperventilation and lethargy. The dramatic cortisol response to incremental NO3- and the return to near-basal cortisol levels after NO3- dilution demonstrated that the homeostatic regulation of cortisol remained functional after NO3- exposure. It also indicates that even partial reduction in aquatic NO3- levels can facilitate return to normal feedback regulation of cortisol. The absolute levels of cortisol increased with each NO3- addition, but these increases were not significant. This study also suggests that NO3- intoxication of aquatic wildlife warrants more complete examination. While fecal cortisol measurement has been previously reported for marine fish, the present study is the first assessment of fecal cortisol in freshwater fish and demonstrates that this methodology can be useful as a noninvasive indicator of NO3 – induced stress.
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:fish cortisol stress elisa
Date of Publication:01/01/2008