MARCO ISLAND — Florida wildlife researchers are trying to get to the bottom of what killed clusters of catfish in waters around Marco Island last week.
Reports of the catfish kill surfaced before Thanksgiving along with uncharacteristic schools of catfish swimming erratically at the surface of Henderson Creek south of U.S. 41 East.
"That was a big indication that something was strange," Rookery Bay National Estuarine Research Reserve spokeswoman Renee Wilson said.
Instead of being silvery gray, the fish were ghostly white and had reddened lips and fins, a sign that the fish were under some kind of stress, she said.
Reserve workers sent off tissue samples from the dying fish to the Fish and Wildlife Research Institute, the science arm of the Florida Fish and Wildlife Conservation Commission in St. Petersburg, to be tested. Results could take weeks.
Researchers wouldn't speculate about the cause of the Marco Island fish kill, one of about a thousand that get reported to the wildlife agency each year from around Florida. Theories range from red tide poisoning to a disease or virus.
"We don't want to jump to a conclusion," said Theresa Cody, associate research scientist at the institute.
Collier County pollution monitors reported Friday that they have received isolated reports of dead catfish in upper Henderson Creek, in a back bay near Caxambas Pass on Marco Island and at the Port of the Island marina off U.S. 41 East.
Wilson said Collier County took water samples from Henderson Creek, but they didn't show anything out of the ordinary or test positive for red tide, a bloom of microsopic algae that can emit a toxin that kills marine life and causes respiratory irritation in humans.
Water samples collected Thursday from Barefoot Beach, Vanderbilt Beach, Seagate, the Naples Pier and South Marco Beach all tested negative for red tide, pollution monitors reported Friday.
Satellite imagery still shows elevated to high levels of chlorophyll along the shore of southern Collier County, a possible indication of red tide.
Offshore winds through the weekend should minimize effects at the beach, but the county still is warning people with asthma or emphysema to be cautious about going to the beach to avoid worsening their condition.
Catfish are mostly bottom-dwellers, where red tide sometimes settles out. In 1996, an especially deadly red tide coincided with another catfish kill in Collier County. That fish kill was blamed on a virus.
The Department of Health hasn't issued any warnings about eating catfish, and a spokeswoman couldn't be reached Friday for comment on the fish kill.