Environmental enrichment in fish aquaculture: A review of fundamental and practical aspects

Abstract

Environmental enrichment (EE) can improve the welfare of captive fish. Its objective is to provide new sensorial and motor stimulation in order to help meet their behavioural, physiological, morphological and psychological needs, whilst reducing stress and frequency of abnormal behaviours. In fish farms, rearing environments are usually designed from a human perspective and based on economic requirements, mainly for practical reasons for the farmer, with little consideration for animal welfare. Throughout aquaculture production cycles, many farming operations can be stressful for fish, and EE may not only help them cope with these stressful events but also improve their overall welfare. In recent years, increasing interest on the effects of EE in captive fish has focussed mainly on structural enrichment. However, there are many other enrichment strategies that merit attention (e.g. sensorial, occupational, social and dietary enrichment) and which may be of interest for fish farming. Here, we review in depth the existing literature on EE and its effects on the welfare of a wide range of farmed fish species, discussing the feasibility and potential applications of different EE strategies to promote fish welfare at a commercial scale. We also present a practical framework to address the design, validation and implementation of EE by the aquaculture industry, taking in consideration the technical challenges of providing enrichment for farmed fish.

Waves and currents decrease the available space in a salmon cage

“…While there were some effects of waves and currents on swimming effort, neither had a major effect, and the low speed at which the salmon switched to standing on current might indicate that they prefer to do so at this site. Literature suggests that forcing salmon to exceed their preferred swimming speed might have a negative influence on salmon [57], but considering that current speeds rarely reached one body length per second (1 BL s -1 ) at this site, this is unlikely to be a problem for these salmon, and might in fact perform the role of environmental enrichment instead [58, 59]. Considering that salmon were also seen less in the “East” camera, there is clear indication that even at low currents, salmon in this cage do not perform a circular swimming pattern using the entire perimeter of the cage as is seen in other farms [23, 60].…”

Waves and currents decrease the available space in a salmon cage

“…While there were some effects of waves and currents on swimming effort, neither had a major effect, and the low speed at which the salmon switched to standing on current might indicate that they prefer to do so at this site. Literature suggests that forcing salmon to exceed their preferred swimming speed might have a negative influence on salmon [57], but considering that current speeds rarely reached one body length per second (1 BL s -1 ) at this site, this is unlikely to be a problem for these salmon, and might in fact perform the role of environmental enrichment instead [58,59]. Considering that salmon were also seen less in the "East" camera, there is clear indication that even at low currents, salmon in this cage do not perform a circular swimming pattern using the entire perimeter of the cage as is seen in other farms [23,60].…”

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

“…Among these challenges, the welfare of captive fish can be severely affected by a wide number of stressors involved in routine husbandry [3]. In this sense, the application of environmental enrichment (EE) can help to improve the welfare of captive fish [4,5]. Among different EE strategies, the addition of physical structures in the rearing environment (i.e., structural enrichment) increases the heterogeneity and complexity of the rearing environment, providing diverse effects on the growth performance, physiology, behaviour, and health of farmed fish [6,7].…”

“…Adding suspended ropes to experimental sea cages of on-growing seabream increased the spatial use of fish in the net-pen [10]. Nevertheless, the existence of null or contradictory effects of structural enrichment on behaviour, physiology, and growth performance on other fish species of aquaculture interest highlights the need for further species-specific studies on the design and particular effects of different enrichment strategies [4,7].…”