Under intensive culture conditions, fish are subjected to increased stress that has negative impacts on the fish overall performance. Though good management practices contributes to reduce stressor effects, the possible role of the diet quality in modulating acute stress response has been poorly investigated in fish. The objective of this study was to evaluate the modulation of acute stress response by different diets in marbled trout, Salmo marmoratus. Twelve groups of trout fingerlings (150 mg ABW) each consisting of 1000 specimens were randomly allotted in triplicate to four commercial trout diets (S, B, D, V) differing in ingredient and nutrient composition (12-20% lipid and 51-59% protein). Fish groups, kept under controlled rearing conditions (water temperature 8.5-10°C) in a flow-through rearing tank system, were fed over 148 days at 3% body weight/d-1 in two daily meals. At the end of the trial one group of fish per diet was subjected to a standardized protocol of disturbance simulating an acute transportation stress (1 hour at 4.5 fish/L) and sampled 1 h after exposure. The fish remaining in the tanks were used as controls. Modulatory effects of dietary treatments were evaluated by means of cortisol level measured by RIA in plasma, fins and skin mucus and associated to the growth performance and mortality observed in the feeding trial. Diet B resulted in the poorest survival (59.2 vs 70.0%, P<0.05) and in the lowest weight gain relative to all the other diets which gave rise to similar responses (703 vs 1100% IBW, P<0.05). Moreover, fish fed diet B showed the highest cortisol burst after transportation in all matrices (4- 12 folds higher than controls), such an increment being an adverse response against the stressor. Cortisol significantly increased in all matrices after the transportation stress (P<0.01), but only in plasma a significant effect of the past diet (P<0.05) has be detected. The results showed that a poor diet, beyond reducing growth and survival, can also affect fish acute stress response and that cortisol levels measured in non-invasive matrices such fins or skin mucus proved reliable to study acute stress response in marbled trout.
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- fish remaining