Most salmon farming systems involve practices that expose animals to acute handling stressors, which have negative consequences on behavior, growth, performance and survivability. Sedatives or anesthetics are commonly administered to fish to mitigate these consequences (Aydin & Barbas, 2020) . Nevertheless, these products can cause mortality and damage to fish. The present experiment aimed to study the effect of an antistress functional feed additive (AFFA) mainly based on proprietary blend of essential oil bioactives, on the stress induced by handling and crowding subsequent stages.
500 Atlantic salmon ( Salmo salar ) with an average weight of 196.74 ± 2.88 grams were equally divided into 5 tanks at a stocking density of 30.27 kg/m3 . The fish received a standard pelleted diet and after a 14-day acclimatation period, each tank labeled from A to E was exposed to the following in-water concentration of AFFA; A-0 ppm (negative control), B-20 ppm, C-40 ppm, D-60 ppm and E-20 ppm at time 0 min + 20 ppm at 2 hrs. The fish were transferred to external containers 35 min after the addition of the AFFA and crowded to a density of 85Kg/m3 to reproduce typical conditions of salmon transportation. These containers contained the same concentration of AFFA as the
original tanks. Fish stress responses were measured through: behavioral observations, cortisol levels at 5 different times following the AFFA addition (0 min, 35 min, 2 hrs., 4 hrs. and 48 hrs.) and time to reach a 30% oxygen depletion after transfer. Finally, feed resumption was measured from the transfer on each batch. Data were analyzed using ANOVA (General Linear Model) when appropriate.
Regardless of the essential oil bioactives
concentration, salmon’s body orientation wasn’t affected through the study and was similar to control fish. However, at 4 hours, fish in treatments
C and D were excited while a decrease of swimming activity was observed in treatments B and E, compared to the control one . The oxygen depletion time was significantly the longest for fish in treatment E and the lowest for control fish (17. 4 vs. 11 min; p=0,054). One day after the transfer, treated fish from treatment E
displayed a quicker resumption of feed intake compared to the control fish (2.05 g vs. 0.69 g). The cortisol level observed in each group was increased from 35 min (P <0,001), which indicates a stress response to the experimental transfer model . It became significantly lower (P<0.05) in treated groups 4 hours post-treatment, and once again Group E stood out displaying the lowest cortisol level at this time compared to the control fish (204 vs. 547 nmol/l; P<0,01).
These results suggest the potential of using
an AFFA for fish sedation at 20-ppm concentration repeated every 2 hours.