Environmental enrichment induces changes in brain monoamine levels in gilthead seabream Sparus aurata

Abstract

It is generally accepted that environmental enrichment enhances the performance and improves welfare of animals kept in captivity. Similar results have been obtained for fish. It has been previously reported that the presence of Blue or Red-Brown Substrate (BS and RBS respectively) on tank bottom resulted in growth enhancement and suppression of aggressive behavior of gilthead seabream Sparus aurata compared to Green Substrate (GS) and tanks without modifications (Control-C). In an attempt to identify the underlying mechanisms, in the present study the effects of this environmental enrichment on brain monoamine neurotransmitters and fatty acids of gilthead seabream were evaluated. BS and RBS fish had lower serotonergic activity (5-HIAA/5-HT), resulting mainly from lower 5-hydroxyindoleacetic acid (5-HIAA) levels. BS fish also had lower serotonin levels compared to all other treatments. Brain noradrenaline (NA) levels did not show significant differences between substrate treatments and control. Brain dopamine (DA) levels were lowest in BS and RBS fish, higher in GS fish and highest in C fish. No differences were observed for dopamine metabolites or dopaminergic activity. Moreover, brain NA was negatively correlated with body weight in BS fish and positively correlated in RBS and C fish. A positive correlation was also observed for brain DA with body weight in RBS fish. No differences were observed for brain fatty acids. Present results support the hypothesis that the beneficial effects of the presence of BS and RBS are related to altered social interactions and indicate the establishment of a less stressful social organization in enriched-reared fish groups.