Abstract
Both the conventional and organic aquaculture sectors have grown rapidly over the past few years. Moreover, welfare has attracted increased attention on the part of both consumers and governments. However, fish welfare assessment is complex and thus needs to adapt measurements that are easily applicable to aquaculture conditions. In this study, in addition to classical welfare indicator measurements (physiological stress indicators and growth performance), we recorded the swimming activity data using acoustic transmitters to evaluate the welfare of European sea bass (Dicentrarchus labrax) fed a conventional vs. an organic diet. Prior feeding trial, the swimming activity recorded by tag has been calibrated with water speed during critical swimming speed (Ucrit) tests. This calibration allowed us to increase the power of the recorded data, providing information on swimming activity with respect to the Ucrit value and on the metabolic cost of swimming. After a four-month experimental period, physiological stress indicators and growth performance did not differ significantly between the two diet groups. However, we observed a subtle difference in swimming activity: the fish in the organic diet group were more active during the feeding period in the morning. All indicators considered, our results suggest that an organic diet does not incur higher metabolic costs and does not affect the welfare of the European sea bass. Moreover, this study shows that the use of acoustic transmitters previously calibrated with physiological indicators, such as Ucrit, is a promising tool for welfare monitoring in aquaculture conditions.
Highlights
Due to an increasing demand for fish products and a decrease in natural resources, the aquaculture sector has grown rapidly over the past decades, representing more than 50 % of total fish production (FAO, 2018)
We evaluated some physiological indicators of health and welfare, swimming activity and growth performance of European sea bass under two different feed regimes
Swimming activity was measured using acoustic transmitters previously calibrated with the swimming performances during using a critical swimming speed (Ucrit) trial, allowing better qualification of swimming activity during the experimental period according to the diet
Summary
Due to an increasing demand for fish products and a decrease in natural resources, the aquaculture sector has grown rapidly over the past decades, representing more than 50 % of total fish production (FAO, 2018). Many innovative approaches using fish spontaneous swimming activity and/or behaviour as a reliable proxy of fish welfare have been developed (Martins et al, 2012) This can be achieved using classical video recordings (Alfonso et al, 2020b; Sadoul et al, 2017, 2014; Stien et al, 2007) and acoustic transmitters that record several variables, such as positioning, speed or acceleration. Having previously been widely used for monitoring natural fish pop ulations for conservation purposes (McKenzie et al, 2016), these transmitters are being increasingly used in aquaculture contexts for fish welfare monitoring (Carbonara et al, 2020a, 2020b, 2019a; Gesto et al, 2020; Munoz et al, 2020) Their use appears promising for monitoring welfare, as they allow evaluations of the behaviour of free-swimming fish over long periods (Halachmi et al, 2019) without affecting welfare and biological performance (Alfonso et al, 2020c; Jepsen et al, 2011). The signals recorded by the transmitter can be prior calibrated with other physiological variables, such as muscle activity and swimming performance, thereby increasing the power of the phys iological data obtained (Clark et al, 2010; Martos-Sitcha et al, 2019; Wilson et al, 2013; Zupa et al, 2015)
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