Madureira, T. V., Costa, J. L., Malhão, F. et al. 2019. Design of a multi-parametric profile for assessing the acclimation period of juvenile brown trout after an acute transport to new housing environment. Applied Animal Behaviour Science 219, 104835.
Fish batches are often transported from aquacultures to laboratory facilities, and this fact triggers a pre-stressed condition that can cause alterations in both physiological and behavioural status of animals. The acclimation before fish trials is highly recommended to ideally ensure basal levels for the species, but there is still limited information concerning the period of time and parameters to be included for the evaluation. Facing those facts, brown trout (Salmo trutta f. fario) juveniles subjected to an acute transport (around 2 h) were here tested during 42 days post-stress (at 12 h, 7, 14, 28 and 42 days), in order to: 1) define a multi-parameter approach, based on biochemical, physical, morphological, nutritional and behavioural parameters that best characterize the fish acclimation and welfare status; and (2) propose an adequate acclimation period for brown trout juveniles after transportation to new housing conditions. Behavioural changes were noted with an overall stabilization at the 17th day. Fish tended to occupy preferentially the bottom of the tank, a smaller number of tank sections, decreased the swimming activity and the number of abnormal movements. Reaction time to food decreased until it was instantaneous, and the reaction to food gradually changed over time, so that on the 1st day there was no reaction and, from the 30th day, most of the fish moved continuously to reach the food. Feed intake did not occur on the 1st day, and then increased gradually. Despite that, there were no differences in fish condition and hepatosomatic indices over time. In general, glucose was relatively stable along the assay, and cholesterol decreased at the 7th and 14th days, compared to 12 h, possibly as a consequence of the high metabolic demand induced by stress. Cortisol varied from 21,841.9 pg/mL (12 h) to 2162.2 pg/mL (42 day). As for cortisol, the volume-weighted nuclear volume of interrenal cells was not significantly distinct between sampling days, but a minimum of 96.33 μm3 was reached at 28 days. Higher haemoglobin values were obtained at 28th and 42th days, in relation to 12 h and the 14th day. Triglycerides, potassium and haematocrit did not change. The quantitative skin analyses (fragments and histological sections) showed a reduction in the pigmented area, with stabilization at 14th day. Acclimation of brown trout juveniles should be monitored using a multi-parameter evaluation including behavioural, biochemical, nutritional and morphological analyses. Overall, it is recommended an acclimation period of at least 28 days.