LAUSR

Abstract Knowing the best conditions to culture fish it is an important issue for aquaculture. Stocking density and routine handling are two factors with a great influence the outcome. This experiment examined the effects of different rearing conditions, corresponding to medium density (10 kg/m3; MD), high density (20 kg/m3; HD), low density (5 kg/m3; LD), and handling (at 10 kg/m3; H), on the liver and plasma physiological parameters of the total antioxidant capacity (TEAC), lipid peroxidation (MDA), cortisol levels, Adrenocorticotropic hormone (ACTH), glucose and alanine aminotransferase (AAT) in gilthead sea bream, Sparus aurata, as well as its social kinetics and individual responses to behaviour tests. The handling, was simulated by placing a dip net into the tank and allowing it to remain still for 20 s once a day. The capture of fish for behaviour test involved further handling and disturbance that was considered as acute stress. The fish were sampled at 15 and 30 days. The results showed major growth in fish subjected to LD at 15 and 30 days, at 30 days, significant differences appear between HD and LD. The TEAC, MDA, ACTH, cortisol, glucose and AAT levels in the plasma did not differ significantly among the experimental lots and over time (15 and 30 days), but plasma cortisol appeared to be high in MD at 30 days compared to 15 days. The main response to acute stress was a decreased response capacity with a lower increase in ACTH, cortisol and AAT at 30 days. The results of the behaviour tests; open field test (OFT), neophobia (NEO), object presentation repeat (ORP) showed that the most frequent movements were “escape” and “static” among all of the tests and treatments, while “contact ‘ and “avoidance’ were less frequent. However, few differences were found among treatments, but the large variation among individuals in all of the treatments was remarkable. On the other hand, the results showed that fish reared at a low density exhibit less total movement but are more diversified in their responses to individual behaviour tests and social kinetics.