Effect of Ashwagandha (Withania somnifera) Root Powder on Thermal Induced Stress Responses in Nile Tilapia (Oreochromis niloticus)

Abstract

High growth rate with efficient tolerance against environmental stress agents are the two most important character acknowledged in modern aquaculture. O. niloticus is the most cultured species after carps worldwide, which is known for its lower tolerance to cold shock. Certain studies have been conducted to address this issue by incorporating various feed additive and plant extracts in the fish feed. The present study was conducted to evaluate the possible role of Ashwagandha (Withania somnifera) root powder in enhancing stress tolerance of O. niloticus to cold shock. A 80 days trial was conducted, and a total of 90 fish (Initial body mass=90g) were randomly distributed in 6 fiberglass tanks capacity,100L stocking density (1.5g/L). The tanks were divided at random into two groups and experiment was conducted in triplicates. One group was fed with basal diet without Ashwagandha root powder (D1), while second group was fed with Feed having 15% Ashwagandha root power inclusion (D2). After 80 days growth performance was noted and then both groups were subjected to cold shock (15°C.) for a period of 2 h. The fish were the anesthetized with MS-222, taking blood from the caudal vein for hematological analysis while dissection was done in the cold chamber for taking samples for the assessment of antioxidant enzymes activity. The water quality parameter including water temperature (27-29°C), pH (6.5), ammonia, was maintained throughout the experimental trial by changing 20% water having same temperature after every 3 days. Results indicated significant improvement in growth performance; FBW (Final Body Weight), TWG (total weight gain), and SGR (specific growth rate) along with improved FCR in D2 compared to D1. A Post cold shock hematological indices have shown a decrease in in RBC hemoglobin (Hb), hematocrit (Hct), mean corpuscular hemoglobin (MCH) and (%), mean corpuscular volume (MCV) count in D1 fish compare to D2. Furthermore, activity of metabolic enzymes ALT, AST and LDH increased in D1 compared to D2. Owing to antioxidant activity in liver and kidney univariate analysis has revealed a significant Organ× diet interaction. Significantly high SOD and CAT activities were observed in the liver and kidney of D2 group followed by D1 while POD was enhanced in liver and kidney of D1 followed by D2. However, LPO activity was higher in D1 (both liver and kidney) compared to D2 group. Similarly, cortisol releasing hormone (CRH) expression in the brain tissue as well as blood plasma cortisol level was significantly higher in D2 compared to D1. These results suggest phenomenal impact of Ashwagandha root powder in reducing stress in O. niloticus which is evident from the decreased vi plasma cortisol level in blood after cold shock in D2 compared to D1. However, further study regarding the optimum inclusion rate and molecular study related to stress genes, is recommended. Key words: Cold shock, Thermal tolerance, Withania somnifera, Oreochromis niloticus, antioxidant activity.