Fish in the wild or culture are susceptible to parasitic infection which may cause mass mortality or significant economic loss. In some circumstances, parasites provide a route for secondary infection by various microorganisms. There are a diverse group of parasites in the aquatic environment and each and every type of parasites cause different damage to the hosts. However, their population diversity and distribution are altering over the time as a result of global climate change and anthropogenic interventions. The aim of my study is to characterise selected parasites from commercially important fish in the south-eastern region of Australia. Proper identification/characterisation will be central in studies focused on population structure, important life-cycle, diversity, distribution, and host-parasitic interactions. The outcome of this study will also crucial for the sustainable management of the marine ecosystem.