Intensive systems of aquaculture favors occurrence of diseases. Purified extract of saponins from Quillaja saponaria are characterized by their ability to interact with biological membranes, stimulate the activity of immune cells such as macrophages, and increase the production of cytokines. Therefore, saponis work to modulate the immune response, promoting natural resistance against fish pathogens, including Francisella orientalis. The objective of this study was to evaluate the effects of dietary supplementation with Q. saponaria on resistance of Nile tilapia against francisellosis.
Nile tilapia (172.7 ± 16.6 g) were stocked in tanks (500 L/ 25 ± 1.5 °C). Fish were kept for two weeks for acclimatization to the laboratory condition. Fish (n = 240) were randomly distributed into two groups, with four replications each. The experimental diet was formulated with purified extract from Q. saponaria (0,5 g/Kg) (QS) and a basal diet without supplementation was used as control group (CG). The experimental diets were produced by extrusion. A horizontal mixer was used for blending the dry ingredients, and extrusion was performed using an extruder. The feed was provided four times a day until apparent satiety. Fish were fed the experimental diets for sixty days and after which they were subjected to challenge with F. orientalis (105 CFU/ml).
As results, during the observation of behavior and clinical signs, it was found that QS group recovered faster from the infection than control group. It was confirmed by the reduction in clinical signs and recovery of feed intake. Cumulative mortality of fish fed with QS (31.8%) was lower than CG (55.6%) over the twenty one days after the challenge (p < 0.05). There was a reduction in the re-isolation of F. orientalis in the groups fed with QS. Our results highlight the importance of using saponis to control franciselosis in fish farming. Q. saponaria have been shown to be effective to improve survival of Nile tilapia and destroy the bacteria.