Environmental Enrichment for Rainbow Trout Fingerlings: A Case Study Using Shelters in an Organic Trout Farm

SIMPLE SUMMARY: Enriching the places were captive fish live, i.e., tanks, ponds or cages, has demonstrated potential to improve the wellbeing of the fish, which is a matter of increasing concern in the aquaculture sector. Enriching strategies are diverse but studies on the feasibility of their implementation in real farming scenarios are scarce. Here, the feasibility of using structural enrichment in the form of plastic shelters to improve the welfare of rainbow trout was studied in an organic fish farm. It was demonstrated that the use of simple plastic shelters is technically feasible, since the shelters induced little extra work in the farm routines and had no negative effects on fish performance, health or mortality. However, different to laboratory-based studies, the fish did not develop a clear shelter-seeking behavioral response when disturbed. This could be related to the short duration of the study, and therefore, it is recommended that enrichment in real scenarios should be tested covering a relevant part of the life cycle of the fish. ABSTRACT: Physical enrichment can improve the welfare of captive fish. Previous research has shown that fish often show preference for enriched environments, which can also result in improvements in growth performance. However, effects of enrichment are not always positive and the design and extent of the enrichment needs to be carefully considered. In this regard, information in real aquaculture scenarios is limited. The aim of this study was to serve as a proof of concept to test the feasibility of using simple PVC immersed shelters as a tool for better welfare in an organic rainbow trout farm. Our shelters induced little extra work in farm routines and had no negative effects on fish performance, health or mortality. The behavioral assessment pointed to a preference for sheltered areas in undisturbed conditions. However, no benefits were observed in terms of stress responses during standardized stress tests, and fish showed no obvious shelter-seeking behavior after disturbance. The results in terms of shelter-seeking behavior were probably limited by the short duration of the experiment, which was due to the farm’s routines and needs. It is recommended that strategies for enrichment in real scenarios should be tested covering a relevant part of the life cycle of the fish in captivity, to fully account for their potential to improve welfare in aquaculture.