Effect of feeding delay after self-feeder activation on growth performance and feeding behaviour of red porgy (Pagrus pagrus L. 1758): application to submergible cages with surface hopper

Red porgies (Pagrus pagrus) of 20.6 +/- 1.5 g mean weight were reared in tanks under four delayed self-feeding conditions (0 = control, 7, 30 and 90 s) after rod activation. The time intervals were chosen to simulate the time taken for a commercial pelleted feed to transit the tube linking a surface-mounted feed hopper and the depth at which a cage might be submerged. Daily feeding rate, growth, food conversion index and condition factor were quite similar but fish behaviour differed among conditions. Fish remained close to the feeding point in the first two treatments (0 and 7 s delay) but foraged more widely in the remaining treatments (30 and 90 s delay), only reconsolidating around the feeding point a few seconds before feed was released. Results are discussed in relation to learning capacity and adaptation of fish to feeding behaviour flexibility, in order to develop reliable self-feeding systems suitable for submerged cages.