Seaweed extracts can be used as natural preservatives in improving the shelf life of different food products. Use of different seaweeds as a preservative is attributed with its total phenolic content, and is known to possess good antioxidant and antimicrobial activity. The seaweeds were extracted in water and their properties as a preservative were evaluated in the present investigation. Padina tetrastomatica was the chosen species for the study due to its high DPPH activity in aqueous media. Three different methods of extraction were carried out at different time intervals. Optimisation was done based on the maximum activity exhibited among the three different treatments. Pangasius fillets were used for the study due to its high fat content and to evaluate the effect of the aqueous seaweed extract as natural preservatives. Chilled storage study was done by dipping the fillets in different concentration of the seaweed extracts as 0.5,1,1.5 and 2% respectively and all the treatments were compared with a control. In the initial optimisation process using the different concentration of the seaweed extracts, a 20 days storage study was carried out. Biochemical parameters, color, texture, myoglobin content and xanthophyll content were analysed to assess the flesh quality. From the results, it was observed that all the treated fillets had better flesh quality and higher shelf life when compared with the control fillets. The control sample got rejected on the 16th day of storage based on the sensory scores and fat oxidation parameters. Nevertheless, the fillets treated with 2% concentration resulted in extending the shelf life by 4 days. It can be therefore concluded from the present investigation that 2% concentration of seaweed extract can be used to extend the shelf life of fillets based on the sensory, biochemical and physical parameters.