Tactile stimulation enrichment affects behavioural and physiological responses of a marine commercial fish species, the gilthead seabream Sparus aurata

Abstract

Fish welfare is gaining increasing attention in both public awareness and research, reflecting a growing recognition and appreciation of its ethical importance in aquaculture. As in nature, reared fish exhibit a range of behaviours and physiological responses suggesting their capacity to experience pain and distress when exposed to deleterious stimuli, however there is a pressing need to aim at the positive aspects of sentience. This study investigated physical and tactile contact as a potential enrichment method for reducing stress and improving welfare in the gilthead seabream Sparus aurata (Linnaeus, 1758). To provide tactile contact, an apparatus made of plastic rods and silicone bristles was used as treatment, while a control setup included only the plastic rods, without the silicone bristles. The experiment lasted 21 days, with fish housed in groups of four per tank. Behavioural assessments were conducted through daily 30-min video recordings, quantifying fish crossing through the bristles, and aggressive displays and attacks. Additionally, half of the fish underwent a confinement stress test on the 22nd day, with cortisol levels and brain monoamines measured to evaluate metabolic stress responses and brain signalling. Individuals in the bristle enrichment group were less inclined to display aggression and showed lower cortisol response after acute stress. Regarding brain monoaminergic activity, differences occurred mostly at two main regional sections: midbrain (central brain section) and hindbrain, both involved in seabream response to acute stress and in connection with bristle enrichment. This is the first demonstration that exposure to tactile stimulation during a limited amount of time is enough to produce behavioural change, mitigate stress responses and modify brain monoaminergic signalling in this important commercial species.