Effects of environmental enrichment on the welfare of juvenile sea bass in captivity

Abstract

[eng] Despite aquaculture is crucial for the global animal production system, uniform and homogeneous rearing conditions can impair the welfare and cognitive abilities of fish. The addition of structural complexity through environmental enrichment (EE) is a recommended tool to ensure or enhance animal welfare. This approach aims to provide novel stimulation to help meet the behavioral, physiological, morphological, and psychological needs of the fish, while simultaneously reducing stress and the frequency of abnormal behaviors. This study experimentally demonstrates the positive effects of incorporating structural EE in rearing environments for juvenile seabass (Dicentrarchus labrax). Seabass were reared in experimental sea-cages for 3.5 months under two treatments: cages enriched with vertical ropes (EE) and non-enriched cages (NE). During the experimental period, muscle and telencephalon samples were collected to assess oxidative stress, and two behavioral tests were conducted: the individual stress response test and the emotional reactivity test. Behavioral analysis demonstrated that EE enhances fish welfare, as evidenced by a more positive cognitive adaptation during high-stress tests. Enriched fish exhibited a greater total distance traveled and utilized a larger area in the emotional reactivity test, indicating a more active exploratory behavior. This behavioral pattern effectively activated muscle enzymatic mechanisms that prevent oxidative damage, reflecting greater physiological resilience under adverse conditions. EE rearing conditions can contribute to achieving positive welfare in farmed seabass, improving their welfare status during captivity. The implementation of this type of physical structure could be feasible in fish farms as a passive system and a non-invasive tool to improve seabass welfare, although further research in this area is crucial.