Dead Fish in Summer? Low Dissolved Oxygen Is Usually the Culprit

One of the most common calls we get during late summer regarding pond management is about a pond full of dead fish, and the owner wants to know what happened. People are worried the water has been poisoned and is unsafe. The vast majority of time, the fish kill is a result of low dissolved oxygen levels in the pond.

Wetlands provide ecological and economic benefits

Wetlands come in many different forms. They can be tidal zones, marshes, bogs or swamps among many other types. However, they all share characteristics that make them wetlands. They are areas where water is present above or near the surface of the soil for at least a portion of the year, and the soil and vegetation present is determined by the presence of water. Some wetlands need to be dry for part of the year to maintain their hydrologic cycle. Wetlands provide several ecosystem services such as reducing erosion, recharging aquifers and providing habitat for several wildlife species.

Seine Sampling a Pond

Seine sampling a pond is a relatively easy way to learn quite a bit about fish, amphibian and invertebrate populations in a pond. Anyone willing to get wet and learn a few fish species can do it. The best time to seine sample a pond is during the summer months – June through September. At least three locations should be seined in each pond; however, more samples generally provide better results, especially in larger ponds. Try to avoid seining spots with wire, sticks, rocks, excessive vegetation or water deeper than 5 feet. Each seine sample should cover a quadrant shaped area.

Rotenone Can Remove Undesirable Fish From a Pond

Sometimes a pond manager wants to change a fishery in a pond by removing existing fish and restocking other fish. This commonly occurs when a pond with fish will be stocked with small fingerlings or when a pond is dominated by bullheads, common carp or stunted bream. Stocking small fingerlings into an existing fish population often gives poor results because existing fish out compete or eat small fingerlings. When overabundant, bullheads and common carp increase clay turbidity of a pond and reduce sport fish production. When bream are overabundant, they interfere with largemouth bass recruitment by eating too many bass eggs and fry, and their small size makes them inappropriate for human consumption and undesirable for angling. A pond manager basically has three options to remove existing fish: drain the pond, stock plenty of large predatory fish (adult largemouth bass primarily are used for this purpose) or treat the pond with a piscicide (chemical that kills fish). Rotenone is the piscicide most often used to kill fish.

A Secchi Disk is Used to Measure Water Clarity

Appropriate water quality is fundamentally important for fish and aquatic plants, and muddy water limits production of both. Ideal clarity for largemouth bass and bluegill production in ponds without substantial vegetation is 12- to 30-inch visibility, with primarily phytoplankton turbidity. Turbidity is cloudiness caused by suspended or dissolved material. Sport fish also perform well in clearer water when substantial aquatic vegetation is present. Ideal clarity for aquatic plant production is generally greater than 36-inch visibility.