Trout succumb to copepod pararsite

Trout in Jackson lake succumb to copepod parasite

Tuesday, December 16, 2008By Rudi KellerSoutheast Missourian

A parasite that is killing trout recently stocked into Jackson City Park's Rotary Lake is not harmful to humans, a Missouri Department of Conservation fisheries management agent said Monday.

Over the past month, about 500 of the 1,300 trout released into the lake Oct. 30 have been found dead along the shore of the lake, said Salvador Mondragon of the Cape Girardeau Regional Office of the conservation agency. The trout appear to have been killed by a small crustacean called a copepod that attaches itself to the gills and inside the mouth of the fish, Mondragon said.
"Usually when you open the mouth, they will be on the tongue or underneath the gill cover," Mondragon said. "It looks like small maggots attached to the gills. It is really easy to notice."
The copepods contributing to the death of the fish do not attach themselves to other species in the lake such as bass, crappie, bluegill or channel catfish. Trout that are properly cleaned and cooked to 140 degrees are safe to eat even if infected with most parasites, the conservation agency said in a news release.

But no one is supposed to be eating the trout at this time of year. Rotary Lake is stocked with trout each year, generally in early November, when water temperatures drop low enough to keep the cold-water loving fish alive. Over the late fall and early winter months, Rotary Lake is limited to catch-and-release fishing for trout.

A season for catching and keeping trout from the lake opens Feb. 1. As water temperatures rise above 65 degrees during the spring, the surviving trout die off. The copepod species infecting the fish also will die off in warm water, Mondragon said.

The fish die-off is being studied to determine if it is worth the cost and effort to restock the lake before anglers are allowed to keep the fish, Mondragon said.

The source of the parasitic copepods is an open question, Mondragon said. They could have infected the fish at the hatchery, he said. But other lakes stocked around the same time have been checked and no significant fish kills have been reported, he said.

That means other factors at Rotary Lake may be contributing to the kills, perhaps too much fertilizer runoff or a lack of food, he said.

There have not been a lot of complaints from anglers using the lake, said Shane Anderson, director of parks and recreation for Jackson. On the Monday before Thanksgiving, he said he noticed 20 to 25 dead fish floating in the water. Typically a few fish die soon after stocking due to the stress of being moved, he said.

The next day, Anderson said he walked around the lake and saw about "200 fish gasping for their life, and they were all trout. We took an oxygen level of the lake, because it looked like they were all having trouble breathing."

The copepods make it difficult for fish to breathe when they attach themselves to the gills.
Anderson said he has been removing the fish from the water as they die, keeping a count for the conservation agency and waiting for lab results to confirm whether the copepods contributed to the deaths or whether some other condition in the lake is to blame.
Cold weather and poor fishing conditions have keep the number of anglers, and complaints, down, Anderson said.

"The common individual thinks there is something wrong with the lake but it is just pertaining to the trout themselves," Anderson said.

rkeller@semissourian.com