Aquaculture is a promising sector of fish industry in the world with about 80 million tones being produced annually. The development of aquaculture faced several constraints; among these are diseases constituting the most limiting factors. Bacterial infections, pose one of the most significant threat to successful fish production throughout the world. In Egypt, bacterial diseases induce heavy mortality in farm fish.The current work was designed to investigate the role of selected immunostimulants (garlic and Echinacea) and probiotics (Organic GreenTM and Vet-YeastTM ) on improving the response of overwintered tilapia fry to vaccination with A. hydrophila vaccine.