Summertime Pond Management
Pond habitat can be simply defined as the environments that aquatic organisms live in and around. However, this definition encompasses a broad list of chemical, biological, and physical categories such as water depth, temperature, and oxygen content which can be impacted by pond bottom conditions and other natural and artificial structures with the environment.
Learning the habitat requirements and preferences of common fishes will help pond owners to not only manage the needs of various life stages of those fishes, but also provide habitat that improves angler success. During the summer months, dissolved oxygen levels become an issue for pond owners, but this can be remedied through water aeration and placement of artificial structures. For example, in most southern ponds, warm season water temperatures are too high and oxygen too low for several of our popular varieties of stocked fish. During summer months, our ponds become uncomfortably warm for fish nearer the surface, but the cooler bottom layer can become depleted of oxygen especially if winds do not regularly agitate the water’s surface. This will lead to large fish kill events in your ponds.
Aeration can help to prevent low dissolved oxygen levels from negatively impacting pond fish populations. In addition, certain types of aeration equipment can effectively mix the water in a pond to prevent water-layer stratification, which can occur in deeper ponds during warm months. Low dissolved oxygen levels can stress or even kill fish, whereas water stratification can limit fish use of cooler, deeper pond areas because of poorly oxygenated water. Anoxic (i.e., lacking oxygen) water does not permit bacteria to adequately process waste products, which then build-up on top of the pond’s bottom sediments. Dissolved oxygen in ponds is naturally affected by photosynthesis, temperature, salinity, wind, supplemental feeding of fish, fish density, and pond depth. The natural sources of dissolved oxygen are photosynthesis by aquatic plants and diffusion from the air. Photosynthesis is the process by which plants (especially algae) use sun light to manufacture food. One of the byproducts of this process is oxygen. In a pond, dissolved oxygen is also consumed through respiration by the living organisms within your pond. The most common dissolved oxygen problem occurs when the consumption of oxygen through respiration exceeds production through photosynthesis and diffusion.
During summer, calm and/or cloudy days may reduce oxygen production by plants while fish continue to respire, and at higher rates as water becomes warmer. On occasion, algae or submerged plants in the pond die suddenly and no longer produce oxygen. As the algae or plants decay, bacteria grow and consume even larger amounts of oxygen. In deeper ponds, fall destratification can cause the dissolved oxygen level to crash as deep, anoxic water mixes with surface water. Although pond fish can survive short periods of low dissolved oxygen concentrations, prolonged exposure can cause stress or even death.
Dissolved oxygen levels can be measured using a chemical kit or an electronic oxygen meter. The preferred times to monitor dissolved oxygen levels are at daybreak and nightfall. The general rule of thumb in determining the need for an aeration system is whether the pond contains greater than 1,000 pounds of fish biomass per surface acre. In most bass/sunfish ponds this carrying capacity is rarely exceeded. However, in fed catfish ponds, this threshold is occasionally exceeded by unknowing pond owners who do not harvest fish appropriately. Often, pond owners derive such pleasure from watching their “pets” grow and feed that they fail to harvest sufficiently to keep biomass within the 1,000-pounds-per-acre limit. For example, a pond owner who stocks 250, 6-inch channel catfish in a 1-acre pond, and feeds regularly, is safe within the limit. But in a couple years when those same 250 fish average 4 pounds each (total biomass = 1,000 pounds), a cloudy, summer morning could spell disaster. Aeration can serve as a pond owner’s insurance against such occurrences. A variety of aeration and destratification systems exist to assist the pond owner. Pump sprayer aerators, surface spray aerators, paddlewheel aerators, diffused air systems, and propeller aspirator pump aerators each bring advantages and disadvantages to each specific pond environment. A thorough review of the sources found in the References section will greatly assist the pond owner in deciding which system best fits any particular pond or budget.
Article by Jessica Rymel, Texas A&M AgriLife Extension, Cass County
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