Nile tilapia (Oreochromis niloticus) is one of the most important farmed fish species in the world, second only to carps. Under intensification, tilapia become more susceptible to elevated stressful conditions and disease infection, leading to high mortality rate and severe annual economic losses. The massive use of antibiotics for disease control in tilapia culture has been under public awareness and criticism. Consequently, several extremophilic bacteria have recently emerged as an ideal and promising growth promoters and disease controllers for farmed Nile tilapia. However, very few studies have considered the potential use of extremophilic bacteria as a feed additive in aquaculture. The present study was carried out to evaluate the use of a novel marine extremophilic bacteria as a dietary supplement on the growth performance, digestive enzymes activity, immune response, and the expression of immune-related genes of Nile tilapia.
Extremophilic bacteria were isolated from marine samples along the Mediterranean Sea. Bacterial isolate showed significant antimicrobial and negative hemolytic activity, with no incidence of disease symptoms, was considered as a safe additive in fish feeds. Pure safe strain was identified, mass produced and incorporated in Nile tilapia diets at four doses; 0 (T0), 2.3 x107(T0.5), 4.6 x107 (T1) and 9.2 x107 (T2) CFU g-1 diet; equivalent to 0, 0.5, 1.0 and 2.0%, respectively. The diets were fed to Nile tilapia fingerlings at a daily rate of 3% of their live body weights, for 60 days. After the termination of the study, growth performance, feed utilization, digestive enzymes activity, immune responses and gene expression were assessed.
The results showed that Nile tilapia fed diets supplemented with extremophilic bacteria at 1% displayed the best growth rates, feed utilization efficiency and digestive enzymes activity. This diet (T1 (1%)) also exhibited a significant increase in cytokines gene expression, hematological, biochemical, hepatic function activities, and immunological parameters, compared to other diets.
Acknowledgement:
This research was supported by the Academy of Scientific Research and Technology (ASRT).