A highly-poisonous toxin may be behind the abnormal mass fish deaths along the central coast of Vietnam over the last three weeks.

This was announced by Agriculture and Rural Development Deputy Minister Vu Van Tam yesterday.

A report, led by Tam, which was made public yesterday, revealed its findings on the cause of some 45 tonnes of dead fish. The fish showed no signs of disease and basic environment parameters were within limitations when the deaths occurred, according to the report.

The Research Institute for Aquaculture No. 1 and the Department of Animal Health – authors of the report – said the only possible trigger for deaths on such a massive scale was a highly-poisonous toxin, which could be biological, chemical or of another kind.

The mass fish deaths have been in the spotlight since early this month when several provinces witnessed the unprecedented sight of dead fished washed up on their shores. The disaster began in Ha Tinh Province and quickly spread to the neighbouring provinces of Quang Binh, Quang Tri and Thua Thien - Hue. Ha Tinh has, so far, reported some 15 tonnes of dead fish, while Quang Tri has reported over 30 tonnes. The other two provinces are yet to arrive at a final figure.

Another report by the Vietnam Academy of Science and Technology (VAST), a state unit probing the mass deaths, also concluded that earthquakes and oil spills were not the cause.

Satellite photos show there have been no big oil spills in the region this month, while seismic stations located in the central provinces, such as Nghe An, Quang Binh and Thua Thien - Hue, did not report any earthquakes over magnitude five on the Richter scale out in the sea in the coastal central region.

The VAST report also denied any effect on Vietnam from the two major earthquakes in Japan on April 14 and 16.

VNS