Comparison of two stunning/slaughtering methods on stress response and quality indicators of European sea bass (Dicentrarchus labrax)

Two stunning/slaughtering methods, ice asphyxia and carbon dioxide narcosis, as common capture procedures in commercial farms, were compared with asphyxia without ice in order to assess their suitability as stunning methods for European sea bass. In this study we have analyzed the stunning effects on the stress response related to fish welfare, and on the meat quality. Sampling was performed 0, 2, 9, 24, 48, 72 and 96 h after death, and for all sampling times, rigor mortis assessment, muscle pH, eye refraction index and sensory evaluation were determined as quality parameters. Moreover, osmolality, glucose, lactate and cortisol were determined as stress indicators. The muscle pH values were significantly lower in CO2 narcosis group from the first 9 h until the end of the study in comparison to the respective zero time. If we compared muscle pH values between each slaughtering method with the asphyxia group through sampling time, we observed statistically higher values in CO2 and ice asphyxia throughout the study. The sensorial evaluation showed a progressive decrease in the three groups analysed versus the respective zero time, although the comparison with the control group showed statistical differences only at zero and nine hours sampling time. Regarding stress indicators, all of them showed significant higher levels after both slaughtering methods compared with the undisturbed group and significant lower levels if compared with the asphyxia group. Our results also show that asphyxia produced a five-fold increase in glucose levels whereas other methods studied only produced a 1.5–1.7-fold increase. Cortisol levels increased 8-fold after asphyxia whereas the other slaughtering methods provoked a 5-fold increase. In summary, the results indicate that both methods are suitable to process fish although the CO2 treatment showed lower lactate and cortisol response compared to asphyxia in ice. In terms of quality, differences between methods are minor.