Fasting up to 34 °C days in rainbow trout, Oncorhynchus mykiss, has little effect on flesh quality

• We determined how fasting and slaughter time affect meat quality of rainbow trout.
• Meat was stored for 72 h to observe its evolution.
• Fasting up to 3 days (34.1° days) does not compromise meat quality.
• Storage time seems to be the determinant factor affecting meat changes.

Pre-slaughter handling of fish can have important effects on product quality, although few studies have related fasting duration with water temperature and flesh quality in trout. In this study, 90 rainbow trout were fasted for 1, 2 and 3 days (11.5, 22.9 and 34.1 °C days, respectively) and slaughtered at 08H00, 14H00 and 20H00 to observe the effect of fasting duration and hour of slaughter on flesh quality indicators up to 72 h post mortem. The values of the fasted fish were compared with 90 control fish kept under similar conditions but not fasted. Results indicate that the interaction between fasting, hour of slaughter and storage time had a significant effect on pH, rigor and water holding capacity, although differences were small. Flesh colour was more affected by storage time than fasting time, with a tendency for higher lightness (L*) values as storage time increased and lower a* and b*-values. Muscle glycogen and R-values were not affected by fasting or time of slaughter, although the high values of the latter indicate some kind of pre-slaughter stress. Overall, these results suggest that fasting up to 34 °C days has little effect on fillet quality.