The improving role of savory (Satureja hortensis) essential oil for Caspian roach (Rutilus caspicus) fry: Growth, haematological, immunological, and antioxidant parameters and resistance to salinity stress

Abstract

Essential oils (EOs) due to their bioactive compounds can be considered suitable dietary supplements to achieve sustainable aquaculture. The present experiment was conducted to evaluate the effects of supplementation of Caspian roach fry (Rutilus caspicus) diet with different doses of savory essential oil (SEO) (Satureja hortensis) on growth performance, haematological parameters, serum and mucus immunological indices, serum antioxidant indices, and salinity stress resistance. Caspian roach fry (2.29 ± 0.07 g) were fed with four experimental diets including basal diet as control, and basal diet incorporated with 100, 200, or 400 mg/kg diet of SEO (SEO1, SEO2, and SEO3 respectively) for 60 days. At the end of the experiment, the lowest feed conversion ratio (FCR) as well as highest final weight (FW), weight gain (WG), and specific growth rate (SGR) were observed in fish given the SEO2 diet (P < 0.05). The SEO3 group showed the lowest FW, WG, and SGR which was significantly lower than other groups (P < 0.05). Survival rate of the SEO1 and SEO2 treated groups showed a significant increase compared to the SEO3 and control groups (P < 0.05) with the highest rates found in fish received SEO2. All groups receiving SEO showed significantly higher haemoglobin (Hb) and number of white blood cells than control group (P < 0.05). The best serum levels of antioxidant enzymes including superoxide dismutase (SOD), catalase (CAT), and malondialdehyde (MDA) were observed in fish treated with SEO2, which showed a significantly different from the control group (P < 0.05). All SEO treated fish showed significant increase in serum total immunoglobulin (total Ig), lysozyme (LYZ), and alternative complement pathway haemolytic activity (ACH50) compared to the control group (P < 0.05) with SEO2 showing the best results. Also significant improvement of mucus total Ig, LYZ, ACH50, protease and alkaline phosphatase (ALP) activities were found in treatments receiving SEO compared to those of control group (P < 0.05). All SEO treatments showed significantly higher resistance to salinity stress than those in the control group (P < 0.05). Overall, our results revealed that SEO inclusion can improve growth performance, antioxidant enzymes activities, immune responses as well as resistance of R. caspicus and 200 mg/kg diet is recommended.