Investigation of growth performance and immune responses of European seabass (Dicentrarchus labrax) after treated with dietary celery (Apium graveolens) and resistance against Vibrio anguillarum

Abstract In this study, we evaluated to reveal the effects of aqueous methanolic extract of celery (Apium graveolens) on the growth performance, immune responses and resistance against Vibrio anguillarum in European seabass (Dicentrarchus labrax). For this purpose, twenty fish (initial mean weight of 4.80 ± 0.06 g) were placed into twelve tanks (400 L) in triplicate and fish were fed with control (C) and three different levels (0.01, 0.05 and 0.1 g/kg) of celery extract-containing diets (AG0.01, AG0.05 and AG0.1) for 30 days. Blood and tissue (kidney, spleen and intestine) samples were taken from the fish every ten days of the study to determine the immune responses of the fish. Respiratory burst activity (RBA) was significantly decreased in the AG0.1 group compared to all other groups on the 10th day of the study. No differences in the RBA were observed on the 20th day among groups. Significantly increased RBA was noticed on the 30th day of the experiment in AG0.01 and AG0.05 compared to C group. Lysozyme activity (LYS) was raised on the 10th day of the study in all celery groups compared to C group. Final mean weight (FMW) was not affected in any experimental groups (P > 0.05). However, in the AG0.05 group, specific growth rate (SGR) increased, and feed conversion ratio (FCR) decreased compared to other groups (P < 0.05). IL-1β in the kidney was highly elevated in the AG0.01 group on the 20th day of the study. Similar results were observed on IL-6, IL-8 and TNF-α expression in the kidney. Anti-inflammatory responses (IL-10 and TGF-β) also increased in all experimental groups and tissues compared to C group. COX-2 was up-regulated on the 20th day of the study in all tissues. At the end of the feeding trial, the survival rate of the AG0.1 group in fish infected with Vibrio anguillarum infection was higher than the C group. Celery aqueous methanolic extract did not affect growth performance directly but increased innate immune responses and the high survival rate. These results demonstrate that celery extract could be used as an immunostimulant feed additive for European seabass at a feed dose of 0.05 g/kg and above.