The researchers studied fish and prawn species in five reservoirs in Sri Lanka. They used nets and hooks to catch fish and prawns throughout 2017. They found that one reservoir had the most species, while another had the least. A type of fish called Oreochromis niloticus was the most common in all reservoirs. Smaller reservoirs had more diverse fish populations compared to larger ones. Factors like fishing methods and weather affected the variety of fish in the reservoirs. Overfishing and harmful fishing practices during low water levels were the main reasons for the loss of fish diversity.