Suspended Structures Reduce Variability of Group Risk-Taking Responses of Dicentrarchus labrax Juvenile Reared in Tanks

Abstract

Structural enrichment is considered a useful tool to improve the welfare conditions of captive fish by deliberately increasing the physical heterogeneity and complexity of captivity environments. However, the potential effects of structural enrichment on the stress response at the group level and on social interactions have not been well studied yet. In this study, we demonstrate that suspended vertical structures (U-shaped ropes) can reduce behavioural variability among fish groups (tank level) of European seabass (Dicentrarchus labrax) juveniles. Differences in behavioural responses during group risk-taking tests (e.g., number of passes per fish) between treatments were detected, and these responses in seabass in enriched captive conditions were more homogeneous among tanks compared to fish from non-enriched tanks. These results suggest a positive effect of the structural enrichment on social stabilisation and response to stressful events at the tank level in seabass. However, further research is still needed to improve the knowledge of the potential effects of structural enrichment on fish welfare and aquaculture management, considering different enrichment designs, intensities, and strategies according to farming conditions, biological needs, and preferences of the fish species and life-stage reared in captivity.

Effects of Water Temperature and Structural Habitat Complexity on the Routine Swimming Speed and Escape Response of Post-Settlement Stage White Seabream

“…There are a few recent studies in the literature that examined the effects of structural complexity on fish (e.g., [33,34,36,[46][47][48]), but their scope is frequently related to welfare under captivity, and is, therefore, more focused on aquaculture/model species and stressrelated endpoints (growth performance, anxiety-like behaviours, brain function). Other studies have made a great contribution to this field by looking at the effects of habitat degradation in the wild, but are focused on tropical reef fish species (e.g., [49][50][51]).…”

Review of the Effects of Enclosure Complexity and Design on the Behaviour and Physiology of Zoo Animals

“…In a captive environment, the primary role of plants is to create an environment that allows animals to express the same type of movements (i.e., act as a locomotor substrate) and as many natural behaviours as in the wild (for species living in a three-dimensional environment). Moreover, the presence of plants and other structures that make the environment more complex, such as perches and ropes, is important to reduce the boredom caused by barren, low-stimulating enclosures, and by the management routine [ 38 , 39 , 40 ]. In addition, these structures help animals to cope with the presence of visitors, as they can provide physical barriers against noise produced by the public [ 41 , 42 ], or provide hiding places in case individuals do not want to be visible to visitors [ 43 , 44 ].…”