Résumé
Pikeperch Sander lucioperca is a species mainly reared in recirculating aquaculture systems (RASs), but it remains very sensitive to stress and handling. Plant phenolic compounds such as quercetin or rutin are frequently investigated as feed additives to improve the growth and well‐being of fish reared in RAS, but their impact on pikeperch and RAS microbial communities has never been studied. Our objectives were to (i) test the effect of quercetin or rutin addition to feed (2.2 g kg −1 diet) on the growth, stress, and innate immunity of pikeperch reared in RAS and (ii) assess the consequence of those additives on the RAS water microbial communities. Pikeperch of 307 (±45) g starting weight were reared in nine experimental RAS ( n = 3) and fed for 84 days on a diet enriched or not (control treatment) with quercetin or rutin (feeding rate: 1.5%). Considering the start (T0) and the end (T84) of the experiment, we compare the fish growth, feed conversion ratio (FCR), morphoanatomical and physiological status, and the water microbial diversity and composition through a metabarcoding approach performed on the 16S rRNA gene. Whereas no effect on fish was recorded with quercetin (624.0 ± 21.9 g final weight), rutin (558.0 ± 10.7 g final weight) reduced pikeperch growth (0.54 vs. 0.69%–0.64% day −1 ), and increased FCR (1.70 vs. 1.2–1.4) compared to control (622.0 ± 16.8 g final weight) and quercetin treatments, respectively. No effect was observed on all fish physiological parameters analyzed separately, but a multifactorial analysis reveals that fish fed with rutin have a different overall physiological state. Quercetin induced a shift in the microbial community structure and composition, whereas there was no effect of treatments on microbial richness or evenness. A dietary supplementation with quercetin or rutin has no or a negative impact on pikeperch growth and physiology and modifies the microbial diversity in RAS. Effects of additives being species‐dependent, precautions must be taken when formulating feed supplements, which must be based on precise studies.