The marine fisheries department conducted a survey in the sea yesterday as marine scientists, environmentalists and port officials are concerned over the epidemic.

During the preliminary survey a huge number of dead fishes, mainly hilsha and other small marine fishes, were found floating on seawater. The officials collected samples for laboratory test to ascertain the cause of the fish mortality.

"We believe the fishes died of pollution from the port city's domestic wastes dumped into the sea and oil spilled out of the vessels calling at Chittagong Port," said Ali Azam, principal scientific officer of Marine Fisheries Survey Department.

"We will probe the matter after further surveys in the affected areas," he said after the initial survey conducted by a team headed by Munir Chowdhury, a magistrate of Chittagong Port.

Deputy Director of the department Sabbir Ahmed also suspected oil spillage for the epidemic. "But we need thorough investigation and laboratory test of the samples."

The epidemic broke out two days after the incident of oil spillage from an oil tanker of state owned Bangladesh Shipping Corporation (BSC) in the port channel.

Immediately after the spillage that spread over 15 km area in the sea, Chittagong Port Authority (CPA) sued the oil tanker MT Banglar Sourav.

A probe body of CPA found that 180 metric tons of crude oil was not offloaded at the time of discharge of imported crude, port officials said. But the BSC officials brushed aside any incident of pilferage of crude from the lightering vessels.

The BSC officials claimed that a portion of the crude oil might have remained as residue inside the tanker after it carried about 15,000 MT of crude from mother vessels.