Recent scientific evidence forfish sentience has stressed the need for novel sentience-based detection tools offishwelfare impairment in commercial farms. In order to mimic a well-characterised stress situation, rainbow trout(Oncorhynchus mykiss) were exposed to poor water quality (hypoxia combined with high ammonia level) forthree weeks (stressed group, S) and compared to a non-stressed control group (NS). After a return to waterquality standard, emotional responses were assessed infish subjected to two potentially threatening situations:(i) social isolation in a novel environment and (ii) human presence. In addition, we used an appetitive-con-ditioning paradigm to determine whether previous chronic deterioration of water quality disturbs cognitiveabilities infish. Spontaneous behaviour in the tanks was also recorded during the environmental challenge as areference forfish activity. We observed that in Sfish, plasma cortisol levels were increased before and aftersocial isolation in a novel environment compared to the plasma cortisol levels in the NS group, despite theabsence of a behavioural difference between the two groups. Under deteriorated water quality,fish locomotoractivity was globally reduced and this reduction was correlated to increased shoaling behaviour. Farmers can usethesefirst behavioural modifications as a sentinel detector forfish welfare impairment. More importantly, wedemonstrated that reactivity to a human presence in a home-environment and food-anticipatory behaviour wereboth inhibited in the S group. We consider that these two sentience-based tests are highly relevant forfishwelfare assessment at the group level and are easy to use in the aquaculture industry.