Growth, production and fin damage in cage-held 0+ Atlantic salmon pre-smolts (Salmo salar L.) fed either a) on-demand, or b) to a fixed satiation–restriction regime: Data from a commercial farm

This experiment investigated the impact of feeding regime upon the growth performance, production efficiency and fin damage of cage-held 0+ Atlantic salmon pre-smolts. Six groups of pre-smolts (n = 61847 ± 2620 fish group− 1) were held in six 12 × 12 × 4 m production cages for 64 days (23rd August until 26th October) at initial and final densities of 4.6 ± 0.2 kg m− 3 and 9.5 ± 0.5 kg m− 3, respectively (mean ± SEM). Fish were subjected to ambient photoperiod (11.67–16.05 h min–max) until 16th October, before being held under 24 h light. Fish were fed throughout the light phase and comparisons were made between three groups fed to an imposed regime (scheduled fixed ration feeding every 10 min) and three groups fed on-demand using commercial interactive feedback systems. The study was divided into primary and secondary phases: during the primary phase (part I) each regime was fed to satiation, whereas during the secondary phase (part II) fish under the imposed regime received a restricted ration that was ca. 20% less than those fed on-demand. During part I there were no differences in ration (g fish− 1), fish condition and Specific Growth Rate (Gw) between regimes (Gw: 1.45 ± 0.06 vs. 1.44 ± 0.04 for imposed vs. on-demand fed fish, respectively). During part II underfeeding in the imposed regime had a significant and deleterious impact upon fish condition, FCR and growth (Gw: 0.45 ± 0.04 vs. 0.84 ± 0.09 for imposed vs. on-demand fed fish, respectively). Fish under the imposed regime also had significantly more dorsal fin splitting than those fed on-demand for the duration of the study, and significantly more dorsal fin erosion at the end of Parts I and II. In addition, the smallest fish within each cage suffered the greatest amount of fin splitting and erosion at the end of Parts I and II, irrespective of feeding regime. Daily ration amongst the on-demand cages decreased as winter approached; stepwise multiple regression analyses demonstrated that this was significantly related to a seasonal decrease in temperature.