The Effects of Passive Integrated Transponder Tagging on Cortisol Release in the Gulf Killifish, Fundulus Grandis

Due to its ease of use, low cost, and essentially limitless number of unique codes, PIT tagging has become the favored technique for tagging individuals in biological studies. However, studies employing PIT tagging generally assume that stress due to the implantation and presence of a PIT tag has no influence on the experimental results. This study investigated the effects of PIT tagging on levels of the stress hormone cortisol in the Gulf Killifish, Fundulus grandis, an estuarine fish of the Gulf of Mexico that is prone to daily or seasonal environmental stressors. Cortisol was measured non-invasively by extracting and assaying cortisol excreted by individual fish into their aquarium water. This technique was optimized by acidifying water cortisol samples and processing them by Oasis HLB 1cc solid phase extraction columns. Measurements of cortisol were taken from water samples prior to, immediately after, and over four weeks after PIT tagging. Overall, there was no significant effect of PIT tagging on cortisol release by fish. There was, however, a significant increase in cortisol release by control non-tagged, as well as PIT tagged fish, immediately after handling, suggesting a stress effect of capture, brief emersion from water, or anesthesia. Cortisol release returned to control levels within one week of the procedure, suggesting that fish be allowed to recover one week after handling prior to other experimental manipulations. Future work will measure cortisol release by uniquely PIT tagged fish exposed to natural and anthropogenic stressors