A team of scientists from the Fisheries Research Institute (FRI) yesterday gathered samples of dead fish from the haors of Sunamganj to identify the real cause of death. FRI chief scientific officer Masud Hossain Khan told The Independent that they need to conduct further studies on the deaths of different species of fish in the haor waters, presumably due to the shortage of oxygen content in the water. The water has become toxic for the fish due to presence of ammonia gas from the rotting boro paddy crops that were deluged by incessant rains since March 29, along with an onrush of water down the Lusai hills across the border. The dissolved oxygen (DO), which is supposed to be 4 to 5 points, was measured at 3.5 points. The DO is critical for aquatic life to survive. The FRI team also collected water samples for tests. Earlier, teams from Mymensingh Agricultural University and the Fisheries Department gathered samples for tests on the water and fish to find out what has caused the death of aquatic fauna, including tiny fish, frogs, leeches and even insects, on such a massive scale. Meanwhile, heavy rains on Thursday and scattered showers yesterday have raised hopes among fisheries officials that the rains would help wash away the toxicity in haor waters and increase their DO levels, enabling the remaining fish to survive. Though rains were scattered today, meteorologists forecast heavy showers ahead.