Maryland biologists remain mystified over the cause of lesions in fish caught on the Eastern Shore's Pocomoke River and plan to assemble a team of experts from state and federal agencies and universities to review their findings.

The state began intensive water quality monitoring at 18 sites in the Pocomoke River and Sound in June, and the sampling is expected to continue on at least a monthly basis through the summer.

"We're taking this very seriously," said Robert Magnien, a scientist with the Maryland Department of Natural Resources who is coordinating the investigation. "We want to get to the bottom of it."

In addition, the state is continuing to sample the river for Pfiesteria piscicida, a flesh-eating algae blamed for massive fish kills in North Carolina. Most tests have turned up negative, though one sample collected by a television reporter and sent to a North Carolina researcher was reported to contain the deadly algae.

Officials say that although Pfiesteria may be in the river, it may not be abundant enough to be responsible for the lesions.

"We're pretty accepting of the fact that Pfiesteria is probably present in the Pocomoke," Magnien said. "It is probably present in most Bay areas that have some salinity, and it has probably been here for thousands of years. But the key thing, in terms of whether it is here, in North Carolina, or anywhere else, is how abundant and widespread it is. Certainly there is no overwhelming evidence that it is common and abundant."

Although Pfiesteria is most often associated with fish kills, Magnien said research also indicates that it can result in lesions without killing fish.

But, Magnien said, Pfiesteria is not linked to all lesions. Research in North Carolina has indicated that wastes from passing schools of fish may serve to trigger Pfiesteria, which spends most of its time dormant in cysts on bottom sediment, to enter the water en masse. They release a toxin that stuns the fish, then begin to eat its flesh.

Lesions from Pfiesteria are most apt to appear in the vent area of fish where wastes are excreted. But Even lesions there may have other causes, Magnien said.

Magnien said the lesions on Pocomoke fish could have other explanations, including contaminants, natural environmental stresses-the river had more fresh water and was more acidic than normal from last fall through this spring-and predation.

Such stresses can make the fish vulnerable to fungi or bacteria infections which lead to lesions.

Watermen have reported finding fish with ulcerous lesions since last fall. Some said that in past months, as much as 40 percent of their catch have had lesions.

Recent fish samples collected by state biologists have found fewer fish with lesions. Those found with lesions in the most recent sampling were in the lower Pocomoke near Pocomoke Sound.

Of 453 fish caught June 19 with watermen near Pocomoke Sound, 12 had lesions. Of 2,426 caught June 17-18 throughout the Pocomoke, only 2 had lesions, and both were taken near the Sound, according to DNR figures.

Magnien said the department has been working with outside experts and hopes to convene a workshop later this summer to review the findings and plan future monitoring and research activities.

Meanwhile, a fish kill involving as many as 10,000 fish occurred in a retention pond located within the Pocomoke watershed in June, but officials say the kill appeared to be unrelated to the lesion issue.

The dead fish, mostly minnows, were found in a stormwater retention pond up a ditch that was connected to the river.

Charles Poukish, who investigates fish kills for the Maryland Department of the Environment, said it appeared likely that the fish had entered the pond during high tide, then could not escape.

An algae bloom found in the pond may have depleted the oxygen in the water and killed the fish, Poukish said. The algae was not Pfiesteria.

"It appears to be a typical type of enrichment, depleted-oxygen related problem," Poukish said.

Poukish said the state typically has one or two fish kills a year that involve more than 10,000 fish.

The DNR has established a special toll-free phone number for reporting fish lesions found in Maryland's portion of the Bay. The number is 1-888-448-0012.