Effect of black cumin seed oil on growth, innate immunity and resistance against Pseudomonas fluorescens infection in Nile tilapia Oreochromis niloticus

This study aimed to investigate the effect of black cumin seed oil (BCSO) on the growth metrics, innate immunity and resistance against Pseudomonas fluorescens infection in Nile tilapia Oreochromis niloticus. This was done by conducting a feeding trial experiment on the fish. A total of four diets (protein, 35.99 +/- 0.16%; lipid, 9.86 +/- 0.06%) varying in their BCSO ration (w/w; 0% (control), 1%, 2% or 4%) were formulated. A total of 180 fish (25.6 +/- 2.2 g fish(1)) were allocated to four experimental groups with three replicates (twelve 150-L glass-tanks; fifteen fish tank(1)). Each fish group was fed thrice a day (8:00, 12:00 and 16:00 h) with one of the four diets at 3.5% of their body weight for 28 days. Following day 7, 14 and 28 of the feeding trial, the growth metrics (i.e. weight gain (WG), specific growth rate (SGR) and food conversion ratio (FCR)) were measured based on bulk weight of the fish tank(1), and the immune parameters (i.e. serum-bactericidal activity (SBA), respiratory burst activity (RBA) and phagocytic activity (PA)) were examined by analysing blood collected from a randomly selected representative fish tank(1). Following the feeding trial course, the fish were injected with P. fluorescens at day 29 and the cumulative mortality was recorded until day 30 post-injection. Obtained results did not show any suppressive effect of BCSO on growth, and showed positive effects on examined immune parameters and survival of all the BCSO-fed fish groups, with best results in 2% BCSO-fed group. At the end of the feeding trial (day 28), SBA, PA and RBA in 2% BCSO-fed fish were increased by 3.66-, 1.94- and 2.85-fold, respectively, when compared to the control. In the same group of fish, the maximum significant (P < 0.05) reduction of post-challenge cumulative mortality (43.33%) was recorded when the mortality was 100% in the control group. Accordingly, this study suggests the dietary inclusion of BCSO at 2% towards controlling P. fluorescens infection in O. niloticus.