Abstract Background: Telemetry applied to aquatic organisms has recently developed greatly. Physiological sensors have been increasingly used as tools for fish welfare monitoring. However, for the technology to be used as a reliable non-invasive welfare indicator, it is important that the tagging procedure does not disrupt fish physiology, behaviour and performance. In this communication, we share our medium-term data on stress physiological profile and growth performance after tag implantation in two important marine fish species for European aquaculture, the sea bream ( Sparus aurata ) and the European sea bass ( Dicentrarchus labrax ). Results: Blood samples after tag implantation (46 days for the sea bream and 95 days for the sea bass) revealed no differences between tagged and untagged fish in cortisol, glucose and lactate levels, suggesting that the tag implantation does not induce prolonged stress in these species. Moreover, the specific growth rates were similar in the tagged and untagged fish of both species. Conclusion: Tag implantation does not have medium-term consequences for the stress physiology and growth performance of these two marine fish species in a controlled environment. These observations support the use of accelerometer tags as valuable tools for welfare monitoring in aquaculture conditions, as they do not affect the fish’s welfare and health. This study also shows that tagged fish can be sampled during experiments and considered a representative portion of the population, as they display growth and physiological parameters comparable to those of untagged fish.