Introduction
Environmental enrichment is now a well-established practice to improve fish housing conditions for a positive state of welfare, both mental and physical (Arechavala-Lopez et al., 2021). Occupational enrichment emerges as a promising strategy for improving the welfare of farmed animals. This form of enrichment aims to stimulate cognitive abilities of animals by providing them with more opportunities to interact with and control their environment. However, occupational enrichment, and its effects on fish welfare indicators, remains a recent and understudied topic in fish production. Predictability of salient daily events, and in particular predictability of feeding, is currently one of the most studied occupational enrichment strategies and can take several forms (Bassett & Buchanan-Smith, 2007). In fish, while temporal predictability (based on the time of day) of feeding has been widely investigated ( Cañon Jones et al., 2012; Chapman et al., 2010; Holley et al., 2014; Sánchez et al., 2009; Ferrari et al., 2016), signalled predictability (based on a signal, such as light or sound) has received little attention (Cerqueira et al., 2017; Galhardo et al., 2011). These studies result in differing effects on fish welfare, depending on the type of predictability used and the ecology of the species. The present study aimed to determine which feeding predictability would be most appropriate for rainbow trout, the main continental farmed fish in Europe, and what the consequences might be for their welfare.
Materials and Methods
We tested four feeding predictability conditions for two weeks: temporal (based on time of day), signalled (based on bubble diffusion), temporal + signalled (based on time and bubble diffusion), and unpredictable (random feeding times). Behavioural and zootechnical outcomes recorded were swimming activity, aggressive and stereotypic behaviours, emotional reactivity, and growth.
Results
Our results revealed that rainbow trout can predict five daily feedings with time as the only predictor as early as two weeks of conditioning. However, this predictor alone also increased aggressive and stereotypic behaviours, suggesting that the use of time as the sole predictor of feedings in husbandry practices may be detrimental to fish welfare. The combination of temporal and signalled predictability elicited the highest conditioned response and the level of pre-feeding aggression and stereotypies tended to be lower than for temporal predictability alone. Rainbow trout were also successfully conditioned to use bubbles as the sole predictor of feeding, and this condition resulted in fewer pre-feeding agonistic and stereotypic behaviours than in the temporal predictability condition. Interestingly, we also found that bubbles were highly attractive regardless of the condition considered.
Conclusions
The use of bubbles as a feeding predictor could be an interesting approach to improve rainbow trout welfare in farms, by acting as both an occupational and physical enrichment.
Acknowledgements
This work was supported by the French funding account CASDAR (Compte d’Affectation Spéciale “Développement Agricole et Rural”) under grant agreement n° 19AIP5919.
References
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