Purdue Ag News Roundup

Most farm-pond fish kills happen naturally, expert says

WEST LAFAYETTE, Ind. -- Every summer, fish die in farm ponds.

According to Purdue University aquaculture expert LaDon Swann, most of these fish kills happen because the pond water lacks oxygen -- not because of chemical contamination.

"Most are due to either an algae die-off or a physical process called thermal destratification or pond turnover," said Swann, an aquaculture specialist with Purdue's Cooperative Extension Service. "Both problems result in decreases in dissolved oxygen levels."

Swann said that when oxygen levels are too low, fish are asphyxiated or die from diseases brought on by the lack of oxygen.

Microscopic green algae plants are essential oxygen-producers in farm ponds. Healthy ponds normally have a faint green color, with water clear enough to see about 2.5 to 3 feet deep. "If nutrients are over-abundant in the water, algae blooms grow, giving the water a green, pea-soup color," Swann said. "Water clarity decreases, limiting visibility to only about six inches."

This is the first warning sign that a fish kill may happen. It's also a critical time in the pond's life cycle, because if the oxygen-providing blooms don't get adequate sunlight, they may die.

Swann said temperature also is a key life-supporting component of farm ponds. It determines the levels of dissolved gases such as oxygen, carbon dioxide and nitrogen in the water. The warmer the water, the less soluble the gas.

While there is no way to completely prevent fish kills, Swann said there are a few precautions farm pond owners can take to reduce the risk:

• Follow recommended fish-stocking densities. Farm ponds generally can support about 300 pounds of fish per acre.
  
• Eliminate unnecessary nutrients by reducing fish feed. This will lower the risk of excessive algae populations, which can lead to fish kills. Various fish feeds contain nutrients that promote algae growth. "Even though it's enjoyable to watch fish eat," Swann said, "feeding does increase the risk of excessive algae buildup."
  
• Control aquatic plants.

To learn more about this and other aquaculture subjects, such as fish farming, visit this site on the World Wide Web: http://www.ansc.purdue.edu/aquanic.
CONTACT: Swann, (765) 494-6264, e-mail: lswann@ansc.purdue.edu

Shotgun fungi stain house siding

This fungus, which can live in wood mulch that surrounds houses, has an unusual method of dispersing its spores. (Spores are the fungi's equivalent of seeds in flowering plants.) These fungi belong to a group known as bird's nest fungi, because they have small "fruits" that resemble a bird's nest with tiny eggs (the spores) in it. "Eventually, the 'nest' opens and the spores are violently shot into the air with enough force to propel them as high as a two-story building", Sellers said.

The fungi are also sometimes known as artillery fungi, which is appropriate, because the organisms can also aim their spores to a certain extent. "The fungus will shoot the spores toward a light source, which will include reflected light that is coming off glass or light-colored buildings or vehicles," Sellers said.

The contents of the exploding cells are sticky, which enables the spores to adhere to plants or passing animals. "The sticky substance is designed to withstand the rigors of animal digestive systems, because some fungi species complete their life cycle by returning to dung," Sellers said. "Attempting to remove the spots from surfaces is generally futile."

To attempt to remove these spots from buildings, Sellers recommends a few methods. Soaking the area with soap and water, followed by gentle scraping, may loosen the spores. However, this method can damage the surface or the paint, so this must be done with care. Diluted bleach may help to remove these spots, but this can also damage the surface or paint, and it can also damage nearby plants if the solution falls on them. Before using bleach water, do a small test in an inconspicuous area first.

To prevent the fungus from splattering your siding or automobile again, Sellers recommends using gravel mulch, stone, pea gravel, black plastic, or some other non-organic mulch next to buildings instead of wood chips. "This will reduce the problem, although this solution may not fit in with the overall garden design," Sellers said. Another alternative would be to add fresh wood chips each year so that the old mulch is completely covered, Sellers said.
CONTACT: Peggy Sellers, (765) 494-7071

Compiled by Chris Sigurdson, (765) 494-8415; E-mail, sig@ecn.purdue.edu
Purdue News Service: (765) 494-2096; e-mail, purduenews@purdue.edu

To the Purdue News and Photos Page