The effect of intermittent feeding on the pre-slaughter fasting response in rainbow trout

• We determined how intermittent feeding affects flesh quality of rainbow trout.
• Fish were subjected to different final feed and pre-slaughter fasting.
• Trout flesh quality was lower in animals subjected to a nine day fast (102 °C d).
• Trout fed every two days and fasted two days (24.3 °C d) showed better flesh quality.

Pre-slaughter fasting, usually measured in days, helps to empty the digestive system but less is known about its effect on fish welfare or flesh quality. We evaluated the combined effects of fasting (measured in degree-days, °C d), preceded by intermittent feeding in the last month of production, on the flesh quality rainbow trout (Oncorhynchus mykiss). Trout (n = 240) were fed the same total amount of food either daily (D), once every two days (2D) or once every four days (4D) for one month, and then fasted for 24.3 °C d (2 days) or 102 °C d (9 days). There was a significant interaction between the effects of intermittent feeding and pre-slaughter fasting for most of the parameters measured. Slaughter weight was higher in 2D and 4D trout after two days of fasting, probably since they had more feed in their stomachs. Muscle glycogen and the hepato-somatic index were also higher in 2D trout after 2 days of fasting, suggesting higher energy reserves. There was no interaction between the effects of intermittent feeding and fasting on final muscle pH which was higher after 9 days of fasting, indicating poorer flesh quality. Overall, the results suggest that trout that received a skip-a-day feeding schedule one month before slaughter, adapt better to a two day fast than trout fed daily or once every four days.