Introduction
Pre-harvest stress in aquaculture refers to the physiological and behavioural changes that occur in fish due to various stressors before they are harvested for human consumption. These stressors typically include handling, crowding, and air exposure and can affect the meat quality and the visual appearance of the fish, ultimately lowering its commercial value and acceptance by the end consumer. Consequences include bleeding, melanosis, texture loss and reduced fillet consistency. Nowadays, more welfare-friendly harvesting methods are being explored (e.g. stunning), but few fish farms have already adopted new equipment and procedures. To address this topic with a solution of comprehensive use in any fish farm, the present work aims at evaluating a novel nutritional approach consisting of a natural anxiolytic to be fed under a short-term protocol before harvesting. The main objectives are to assess the optimal dosage and feeding protocol in European seabass and to measure the impact on stress indicators and postmortem meat quality.
Material and methods
A commercial formulation with no anxiolytic additive was used as a control diet (CTRL). Three additional experimental diets were formulated to include 0.5, 1.0 and 2.5 g/kg of the anxiolytic additive (D0.5, D1.0 and D2.5 diets, respectively). The experiment was held in a marine RAS composed of 15 tanks of 400L capacity. Twenty European seabass of ca. 30 g initial body weight were stocked per tank. The trial had 3 periods: acclimation, phase 1 and phase 2. During acclimation (two weeks) all the fish were fed the CTRL diet. Fish were fed manually to apparent satiation twice per day. In phase 1, CTRL diet was tested in triplicate tanks, whereas the experimental diets were tested in four replicate tanks, and in two replicate tanks in phase 2. During phase 1, fish were fed for 10 days, and after a 48h-starvation, three fish per tank were sampled (sampling 1). During phase 2, the four replicate tanks of the experimental diets were divided in two feeding strategies (approaches A and B), fed for another 10 days, and after a 48h-starvation, six fish per tank were sampled (sampling 2). In the approach A, the two replicate tanks kept being fed with the respective experimental diet, whereas in the approach B the other two replicate tanks switched to the CTRL diet. Before each sampling, a pre-harvest stress event was simulated, consisting of crowding for 15 min, and air exposure for 30 seconds. In each sampling moment, fish were sampled to measure the cortisol level in the plasma, rigor mortis, QIM evaluation at 24, 72 and 168h postmortem, and overall fish quality through, sensory evaluation, texturometer analysis, water activity and total volatile nitrogen.
Results and discussion
Fish stocking occurred with no mortality incidents. The trial is ongoing with the first sampling completed and the samples currently undergoing analysis. The trial is expected to be concluded by mid-April. Upon thorough analysis, all results will be presented at AQUA 2024 as scheduled.