Moderate stocking density does not influence the behavioural and physiological responses of rainbow trout ( Oncorhynchus mykiss ) in organic aquaculture

Abstract

Welfare in farmed fish got particular attention during the last decades from both governmental and public sides. In aquaculture context, welfare concerns are mainly related to handling procedures, water quality and stoking densities. In Europe, authorities had to clarify the threshold limits of stocking densities to maintain fish good welfare, including for organics aquaculture through the EC regulation 710/2009. However, effects of stocking density on fish welfare are complex and sometimes contradictory. Moreover, there is a lack of knowledge about the impact of density on fish welfare in organic aquaculture. Thus, the aim of the study is to asses welfare state of rainbow trout (Oncorhynchus mykiss) at two initial stocking densities (low density, LD: 12 kg/m 3 and high density, HD: 17 kg/m 3 ) fed using organic feed by combining the monitoring of growth performances, behaviour (swimming activity) and physiological indicators (i.e. cortisol, glucose, lactate, hematocrit, red blood cellule count and lysozyme). At the end of experiment, the stocking density reached 21 kg/m 3 and 30 kg/m 3 for the LD and HD respectively. Overall, growth performances, swimming activity and level of physiological indicators of stress and welfare were similar between HD and LD over the experiment duration. To conclude, we observed no alteration of fish welfare between the two stocking densities monitored.This study suggests that a final stocking density of 30 kg/m 3 can be considered for organic aquaculture of rainbow trout respecting welfare. K E Y W O R D Saquaculture, behaviour, fish, organic, trout, welfare

Calibrating Accelerometer Tags with Oxygen Consumption Rate of Rainbow Trout (Oncorhynchus mykiss) and Their Use in Aquaculture Facility: A Case Study

“…Finally, we used the transmitter to follow the day/night oxygen consumption pattern of the fish. Over half of the trout showed a clear higher MO 2 during the daytime compared to nighttime, corroborating previous findings based on the direct measurement of oxygen uptake for this species [ 59 , 70 ], or based on swimming activity recorded by sensors [ 22 , 23 , 71 ]. These previous studies overall observed a diurnal pattern (with two peaks corresponding to feeding), however, in some cases, the trout displayed a nocturnal pattern of activity or lacked a clear pattern.…”

“…For some fish (n = 4/11), the estimated MO 2 decreased over time, while for one fish, the MO 2 increased and we observed no change for the other over half of the fish (n = 6/11). The increase in the MO 2 over time could be indicative of the presence of stressors in the facility, implementing a load on the energetic budget of the fish [ 15 , 23 ]. While at the opposite, a decrease could well represent the acclimatization of the fish to the rearing conditions, which seems to be the case here.…”

“…In addition, the EMG data have also been commonly used in the literature to study swimming behavior and behavioral patterns [ 13 , 19 , 20 , 21 ]. In this sense, the physiological tags are increasingly often being used in aquaculture conditions to monitor fish response to a stressor and/or rearing practices [ 16 , 22 , 23 ], showing great potential in welfare monitoring applications. Indeed, the welfare of farmed fish has recently received considerable attention (e.g., [ 24 , 25 , 26 ]).…”

Surgical implantation of electronic tags does not induce medium-term effect: insights from growth and stress physiological profile in two marine fish species

“…Although these physiological sensors have mainly been used in the wild in the context of conservation and ecology, they have progressively been employed in aquaculture, serving as welfare indicators of common stressors (e.g. slaughtering practices, water quality and stocking density) [4,[7][8][9].…”

Are tagged fish like others? Insights from growth and stress physiological profile in two marine fish species

“…These physiological sensors were mainly used for monitoring in the wild in the context of conservation and ecology, but they were progressively transferred toward aquaculture, serving as welfare indicators in response to common stressors (e.g. slaughtering practices, water quality or stocking density) [4,[7][8][9].…”