Polyvalent vaccinations are a combination of ingredients designed to protect fish against infectious illnesses. They provide comparable or greater protection compared to monovalent vaccines. However, challenges include the need for accessory antigens against viral pathogens, high doses of antigens for protective immunity, and the development of affordable, easily prepared vaccines, particularly for small aquatic animals. These challenges are particularly relevant in aquatic vaccination. The effectiveness of a polyvalent vaccination, ME-VAC Aqua Strept, against streptococcal bacterial infections in Nile tilapia fish, Oreochromis niloticus, was investigated by injection and immersion techniques. In tilapia fish, this inactivated polyvalent vaccination demonstrated a combination defense against many bacterial diseases, including lactococcosis, enterococcosis, and streptococcosis. Modern multivalent fish vaccines that include antigens from multiple pathogens are preferred over high-value fish species such as salmonids. While a high dose of antigens can help to induce protective immunity against viral infections, developing such effective antiviral vaccines can later become a significant challenge. Fish are often more affordable to produce than other aquatic creatures, therefore inexpensive vaccinations are the better choice. The development of aquatic vaccines is also hampered by a lack of technical substance, onerous approval processes, and inadequate promotion activities. Despite these obstacles, a great deal of progress has been made in the creation and production of safe, affordable, and effective vaccines for aquatic animals. It is anticipated that a large number of commercial vaccines will be made available in the coming years, which will significantly support the growth of the aquaculture sector
