FIFTEEN Hong Kong fishermen convicted in Indonesia of destroying a coral reef off remote Irian Jaya while fishing illegally with potassium cyanide are being sought by Interpol. They had already left the country when a court on January 3 sentenced them to 61/2 months' jail, Indonesian press reports said. World Wide Fund for Nature Indonesia representative Dr Russell Betts said a videotape was taken of Hong Kong fishermen in action at the reef. ''They were so confident of the operation that they just ignored divers taking a video of their work,'' he said. ''It shows them tearing apart the coral to get to those fish.'' The names of the boats and crew in the case have been passed on to police. Three Hong Kong vessels - Chui Ah Kuen II, Cheung Fung Mui and Lam Chi Wai - were licensed to operate in Indonesian waters under a charter between the Indonesian fishery firm, PT Gemini Gemilang, and the boats' Hong Kong owner, Handsun Industries Ltd. The chairman of the Cheung Chau Fishermen's Welfare Promotion Association, To Kwong-biu, was not aware of the case, but said potassium cyanide was banned in all waters and local fishermen knew this.