By MICHELE F. MIHALJEVICH
Indiana Correspondent

COLUMBIA CITY, Ind. — A rapid response to fish kill reports is essential in helping applicators determine how the fish died, according to the coordinator of Purdue University’s pesticide programs.

“Solving the mystery is difficult at best, but you need to respond to any fish kill complaint immediately,” said Fred Whitford. “The longer you wait, the more the clues disappear.”

Whitford spoke June 24 during the annual Tri-State Field Day at the Northeast Purdue Agricultural Center. The facility is south of Columbia City in Whitley County.

Fish die for many reasons, including natural mortality, infectious diseases, changing water temperatures and, the most common reason, low oxygen, Whitford said.

“Keep in mind that it’s possible your chemicals did kill the fish, but that it also could have been other things,” he said.

When a fish kill is reported, it’s important to examine physical and biological evidence around the pond or body of water, Whitford said.

“If the dead fish haven’t rotted, take fish and water samples,” he said. “But if they have rotted don’t bother, because it’s too late.”

Vegetation around the water should be examined, and the water temperature noted, he said. Stinky water generally means low oxygen. Dissolved oxygen should be measured at the one foot depth. The applicator should check sites that might drain into the water and prior applications near the area should be noted.
It’s also important to look at biological evidence around the water, Whitford said. The number of dead fish, the size and species should be noted, and the applicator should see if other animals in or near the pond are dead or dying.

“You need to look at all the fish. Don’t just get focused on the big fish,” he said. “You should look for other dead animals. Live animals tell me a lot too, and that is that the kill probably wasn’t caused by chemicals.”

The behavior of the fish may also be a clue as to what caused its death, as oxygen depletion would cause gasping or swimming near the surface, Whitford said. Erratic swimming could be a sign of algal bloom, pesticide toxicity or disease.

Oxygen depletion generally causes larger fish to die first, but algal bloom or pesticide toxicity would cause smaller fish to die first, he said.

The color of the water is also important, as brown, gray or black water generally means oxygen deprivation, and dark green, brown and golden is probably caused by algal bloom.

Applicators should read the labels on all chemicals to be sure they’re staying as far away from ponds as recommended by the manufacturer, he said.

“When you have a pond, it’s special to you,” he said. “And they provide a value for recreation, aesthetics, for wildlife and as retention ponds. If the owners notice dead fish and know you were out there spraying, it’s easy for them to say you killed their fish.
“If you get a fish kill, get out there and deal with it,” he said. “If you wait days, it will be too late because your evidence will be gone. It’s usually a case of low oxygen, but if it turns out to be the chemicals you sprayed, just take care of it and move on.”