<p>Aquaculture plays a vital role in securing the world’s food supply by providing a dependable source of animal protein in an era of declining capture fisheries. Despite its rapid expansion, the sector faces significant challenges, including disease outbreaks, environmental stresses, and concerns over antibiotic misuse. Traditional methods, relying on chemotherapeutics and antimicrobials, have sparked controversy due to residue buildup, antimicrobial resistance, and environmental toxicity. In response, there has been increased focus on discovering new health-promoting strategies. Among these alternatives, synbiotic products resulting from the combination of probiotics and prebiotics have gained considerable attention because of their many benefits. Besides improving disease resistance, synbiotics enhance growth, feed efficiency, gut microbiota modulation, immune regulation, and stress tolerance in fish and shellfish. This review summarizes recent findings on the use of synbiotics in aquaculture, highlighting their physiological effects, mechanisms of action, and potential to reduce antibiotic use. However, gaps remain in understanding optimal dosages, formulations, and long-term impacts, which future research must address. Expanding the use of synbiotics offers promising opportunities for increasing productivity, improving animal welfare, and promoting sustainability in aquaculture systems.</p>