Experts expressed their concern as a 20-kg large catfish was caught on Thursday from the sewerage line in Panthapath in the city. The sewerage system has become a shelter for the catfish, witnesses said.

"As Bangladesh is a flood-prone country, the government should have taken a clear-cut policy before introducing such carnivorous species. If the catfish spread out in our rivers and other wetland areas, it'll eat out all other fish species," said Ainun Nishat, country representative of the IUCN -- the World Conservation Union.

This particular catfish has been living in the sewerage line for years and some others may still remain there, he said.

Experts said people could cultivate catfish in tubs or artificial ponds. But they should not have cultivated it in open water bodies.

Shakhawat Hossain, a resident of Kathalbagan, told this correspondent that he saw two people landing a couple of catfish from the sewerage line of Asadgate last year.

Fisheries Secretary Iqbal Uddin Ahmed told the BBC radio service yesterday that they have stopped encouraging cultivation of such harmful species. However, the government does not have any plan to prohibit the African catfish cultivation, he added.

As many as 14 alien fish varieties are being cultivated in the country, the first of which was introduced in 1953.