The relationship between individual differences in feed efficiency and stress response in African catfish Clarias gariepinus

Despite the importance of feed efficiency and stress response in fish production, the number of studies focusing on the relationship of their individual differences has never been investigated. This study tests whether individual differences in glucose and cortisol responsiveness after an acute stressor can explain differences in feed efficiency of African catfish Clarias gariepinus.Experimental fish were juveniles of African catfish, housed individually. Fish were fed until apparent satiation with a commercial diet once per day. Individual feed consumptions were registered and the residual feed intake used as a measure of feed efficiency. Blood samples for plasma cortisol, glucose and lactate were taken at the start of the experiment (control, indicative of basal levels) and after a stress test (netting) at the end of the experiment. There was a pronounced individual variation in both basal and post-stressor levels. Basal levels of glucose, lactate and cortisol did not contribute significantly to explain differences in feed efficiency. However, glucose levels obtained after the stress test could explain differences in feed efficiency by 12% in experiment 1 and 32% in experiment 2. In experiment 2, the cortisol levels obtained after the stress test also contributed to explain differences in feed efficiency by 17%. These results suggest that high glucose- and cortisol-responders are less efficient fish, suggesting that individual differences mainly in glucose responsiveness explain part of the differences in feed efficiency by explaining variance in maintenance levels.