Selection for growth increases feed intake and affects feeding behavior of brown trout

Growth performance and feeding activities of brown trout selected for growth (S) and control lines (C) maintained without a selection pressure were compared. Groups of 500 fish of each line with the same initial weight (4 g) were constituted and fed for 115 days ad libitum using self-feeders or automatic feeders (2 lines x 2 feeding methods x 3 replicates). After 3 5 days of food deprivation, all groups were re-fed by self-feeders for 46 days. The feeding demands of groups fed by self-feeders were recorded continuously. Growth, feed intake and uneaten feed were measured at regular intervals. In both lines, growth rates were higher in self-fed than in automatically fed fish (P < 0.002), because of higher feed intake (P < 0.03) and better feed efficiency (P < 0.0001). At the end of the feeding period, the mean body weight (BW) was 75% and 64% higher for S than for C in self-fed and 6 automatically fed fish, respectively. Because feed efficiency was not significantly different between the two lines (P > 0.36), the better growth of S was caused by higher feed intake. Self-fed brown trout ate 16-20% of their daily intake at dawn and on average 5% per h thereafter. This feeding activity profile was more discernible for S, which ate more than C at dawn (P < 0.01). M the end of the starving period the loss of weight was slightly higher for S than for C (P < 0.06). It was compensated during the re-feeding period for both lines by hyperphagia and higher feed efficiency. The mean final BW was approximately 90% higher for S than for C. Both lines restored rapidly their own feeding profiles. How this selection process may determine the features of the correlated responses is discussed. (C) 2003 Elsevier B.V. All rights reserved.