Microplastics, defined as plastic particles smaller than 5 mm, have become ubiquitous contaminants in aquatic environments and pose emerging threats to aquaculture sustainability. In aquaculture systems, microplastics enter via multiple pathways, including contaminated aquafeeds, polluted source waters, degradation of plastic-based equipment and infrastructure, and atmospheric deposition. Once introduced, their distribution and accumulation are governed by hydrodynamics, particle properties such as density, size, and shape, and biological interactions, leading to retention in water columns, sediments, and cultured organisms. Ingestion of microplastics by farmed fish and shellfish can cause physical damage, impaired growth, and altered behaviour, while sorbed or inherent chemicals contribute to toxicological impacts such as oxidative stress, endocrine disruption, and reproductive impairment, with implications for seafood safety. Mitigating these risks demands a multifaceted strategy encompassing improved waste and plastic management, the development and adoption of biodegradable or less persistent materials, and the implementation of robust regulatory, monitoring, and awareness measures tailored to aquaculture value chains.