The cause of the illness which wiped out hundreds of fish swept up on Bermuda's shores is still a mystery, experts said yesterday.

Director of Fisheries John Barnes said examination of dead fish samples, both on the Island and by overseas experts, was still underway.

But he said there appeared to be no connection between the dead fish and major fish kills in Maryland and Delaware, which have been attributed to a killer microrganism which thrives in water with a high nutrient content, for example around sewage outflow pipes.

Mr. Barnes said: "Certainly no dead or dying fish have been observed with lesions on their bodies, a departure from the American scenario and we are not faced with large-scale, on-going nutrient input into our waters.'' But he added: "Heavy rainfall in August may have temporarily increased nutrient levels through run-offs into our coastal waters, causing unusual conditions.'' He added water samples taken from Harrington Sound had revealed a bloom of a microbe, but it had not been determined if this was the cause of death for the fish, mostly pinfish.

Bermudian experts earlier pointed the finger at an outbreak of a microbe known as "red tide'' as the most likely cause of the kill.

And he said autopsies of the fish had shown gill infections, which cause fish to suffocate -- but that these were not the primary cause of illness.

Mr. Barnes said: "At this stage, we are undertaking methodical, but time-consuming, examinations of the fish and water and seeking advice from overseas experts in the hope that we will be able to identify the problem.'' He added that the fish kills on the East Coast of the US had been attributed to an organism called Pfiesteria Piscicida (PP).

But he stressed that not all experts agreed on that and many argue that the most likely culprit is a change in the salt or acid levels in rivers, which causes stress and the formation of lesions in the fish.

Mr. Barnes added: "Part of the problem lies in the fact that secondary infections develop very quickly in fish which are stressed and it becomes difficult to isolate the primary infective factor.''