Effects of Phytobiotic Curcuma longa, Allium sativum and Zingiber officinale-Supplemented Diets on Growth, Utilisation of Feed and Nile Tilapia (Oreochromis niloticus) Resistance Against Streptococcus agalactiae

The study investigated how phytobiotic-supplemented diets impact the growth performance, feed utilisation and resistance of Nile tilapia (Oreochromis niloticus) to Streptococcus agalactiae. Fish with a total mean initial mass (37.6 g) of 180 and a random stocking of 15 fingerlings per 150 L tank in triplicate were divided into four groups and fed isonitrogenous (299 g kg⁻¹ crude protein) and isoenergetic (15.7 kJ g⁻¹ gross energy) control diets supplemented with 1% turmeric (Curcuma longa; TUD), garlic (Allium sativum; GAD) and ginger (Zingiber officinale; GID) powder for 56 days. After the trial period, growth performance, feed utilisation and blood health were measured. Ten fish from each replicate were infected with S. agalactiae and mortality was observed for 14 days. The results showed a significantly higher weight gain (g), specific growth rate (SGR; %/day) and average daily growth (ADG; g) in GAD (80.3 ± 1.0, 2.04 ± 0.05 and 1.434 ± 0.02, respectively) and GID (77.03 ± 0.8, 2.0 ± 0.04 and 1.376 ± 0.01, respectively) compared to the control group (60.4 ± 2.5, 1.71 ± 0.02 and 1.079 ± 0.04, respectively). However, these metrics were not significantly higher in TUD (63.8 ± 2.2, 1.8 ± 0.05 and 1.139 ± 0.04, respectively) when compared to the control group. TUD, GAD and GID feed conversion ratio (FCR) and efficiency, as well as protein efficiency ratio (PER), were improved as compared to the control. The haemoglobin (HGB), haematocrit (HCT), platelets (PLTs), white blood cells (WBCs), serum biochemistry and respiratory burst activity (RBA) of TUD, GAD and GID were significantly better than the control. Lysozyme and bactericidal activities were also significantly improved in TUD, GAD and GID as compared to the control. Following the S. agalactiae infection, the fish survival rates of GAD (67.7%), GID (53.3%) and TUD (46.7%) were better than those of the control (26.3%). Dietary supplementation with the above-mentioned phytobiotics in Nile tilapia culture can help to increase production in view of the current challenges posed by the increased incidence of disease in fish farms. They are recommended to enhance growth, immunity and resistance to disease.