Nitric oxide euthanasia: a potential procedure for improving animal welfare and fillet color of tilapia (Oreochromis niloticus)

Tilapia (Oreochromis niloticus) were euthanized with saturated nitric oxide (NO) solution prior to slaughter. The behavior, heart rate, plasma cortisol, and color values were used to evaluate the welfare and fillet color of the fish. Tilapia were unconscious after 20 min of NO euthanasia which was much shorter than with carbon monoxide (CO) treatment. Tilapia remained quiet during the euthanasia process. The heart rate reduced from 41 to 7 beats/min after 20 min of NO euthanasia, and the cortisol level in the NO-euthanized fish plasma was significantly lower than that of the percussively stunned fish sample. Moreover, both the red and white muscles of NO-euthanized tilapia fillets had a brighter red color than those of control, and showed a significant increase in redness (a* values) postmortem at 0 °C for 15 days. The results suggested that NO euthanasia prior to slaughter is a good procedure to improve both the animal welfare and tilapia fillet color. In summary, NO treatment resulted in shorter euthanasia time, less stress, enhanced a* values, and stabilization of tilapia fillet red color. This procedure is valuable for aquaculture of tilapia and possibly other fish species.