Pond management is a dynamic, ongoing process. Regardless of stocking strategy, fish populations will change over time. Major fish population disruptions and their consequences for ponds are described in this article. Pond owners and managers must periodically evaluate ponds to maintain a balanced fish population that assures high quality fish production and recreation.

Environmental and human factors affecting balanced fish populations include:

• Numbers, size and species of fish originally stocked
• Fishing pressure
• Accidental stockings
• Predator / prey interactions
• Cover
• Climatic conditions
• Watershed changes

Despite its artificial placement, a pond is a natural aquatic ecosystem. Like other ecosystems, it undergoes changes that tend to stabilize the composition of communities of organisms in the pond. As fish enter and grow in a newly constructed pond, they use and compete for food and space. The pounds of fish in the pond will soon reach the carrying capacity or maximum weight of fish the pond can support given the nutrients available, space and growing season. Typical Oklahoma pond fish production ranges from 57 - 931 lb / acre and averages 341 lbs / acre. The total weight of fish in the pond can be divided in many different ways. The average 341 pounds may consist of thousands of small, stunted fish; or in a balanced pond, the same weight of fish may be divided among a range of age and weight classes.

A balanced pond provides the fisherman with catchable sportfish and enough small forage fish to keep all age classes growing and in good condition. The concept of a balanced pond is artificial and has no necessary natural counterpart. A pond can be managed to provide a harvestable catch of a single species such as channel catfish or trophy bass; or managed to produce multiple harvestable species, for example, largemouth bass, blue gill and catfish, trophy-sized fish or panfishing. A balanced pond, regardless of the species management goal, is a pond that is managed to maintain a relatively stable population distribution of fish. Nature and human actions make balanced ponds difficult to sustain over time. A balanced pond begins with fish stocking strategies. The original fish stocking plan often determines the fishing quality in the pond.

Numbers and species of fish originally stocked
Most pond owners want ponds to provide angling recreation and occasional fish for the table. A population of fish to meet these demands can be obtained with proper management. Good management begins with a stocking strategy proven to provide quality fishing. There are several species combinations to choose from depending on personal preference and level of management the pond will receive. Common species combinations in Oklahoma are bluegill / largemouth bass / channel catfish, hybrid blue gill / channel catfish, and channel catfish (only if the pond can be fed regularly).

Fathead minnows are often stocked to provide supplemental food for catfish and largemouth bass in new ponds. Fathead minnows can provide a source of small supplemental forage if stocked just before they spawn, however, they are generally completely eliminated from the pond very quickly unless heavy cover is available. It is usually not advisable to stock fathead minnows into ponds containing established populations of large fish. The minnows are often consumed before they can reproduce resulting in very high cost fish food per pound of gain. For example, largemouth bass require about 8 pounds of forage fish to produce 1 lb of bass. Cost of fathead minnows is $9.00 / lb or about $72.00 / lb of bass growth.

Numbers of any fish species stocked per acre depends on level of management and food available to the fish. As noted earlier, predatory fish requires about 8 lbs. of forage fish (bluegill) to produce 1 lb of flesh. This is the reason why many more bluegill must be stocked per acre than largemouth bass.

Bluegill fingerlings, (1-2 in.) are usually stocked at a rate of 500 / acre in the spring time. Spawning occurs in spring and summer. A successful bluegill spawn assures an adequate supply of forage fish for largemouth bass which can then be stocked into the pond in fall or the following spring. Largemouth bass fingerlings (2-3 in.) are usually stocked at a rate of 50-100 bass / acre. 100-200 channel catfish (3-6 in.) can be stocked at this time also.

In 3-4 years this stocking strategy can result in a balanced population of fish that include large catfish, bass and bluegill. There will be adequate supplies of forage fish to maintain this balance under light to moderate fishing pressure. Stocking largemouth bass at the same time as bluegill can prevent fish populations from achieving a sustainable balance. Young bass will prey heavily on newly spawned bluegill and prevent their numbers from increasing sufficiently to maintain a healthy bass population. Some of the newly stocked bass also may be large enough to feed directly on bluegill breeding stock, reducing or even eliminating forage fish before they can reproduce.

Another cause of poorly balanced fish populations in newly stocked ponds is high fish mortality. Fish may have become stressed during transportation to the pond or they may have been infected with disease or parasites. Either condition can kill many of the fish soon after pond stocking.

A common cause of mortality is temperature shock. Shock can be avoided by "tempering" fish, that is allowing them to slowly adjust to differences in water temperature between the hauling tank and the pond. Allow at least 10 minutes tempering time for each degree difference in water temperature. Acclimatize the fish slowly by adding pond water to the hauling tank until temperature in the tank equals temperature in the pond.

Fish eating birds
Cormorants, herons and other fish eating birds also can be the cause of significant mortality in newly stocked fish or any fish they can eat at the time. Scare devices may be necessary in areas where these birds are numerous. The heron decoy pictured in this article has proven effective in keeping most herons off ponds. Only one is needed on most ponds as these birds are solitary feeders and prefer to hunt alone. The presence of the decoy is enough of a negative stimulus to prevent most, but not all other herons from landing on the pond.

Cormorants are large, long necked, dark colored birds about the size of a small goose. They are usually seen in flocks that range in size from few birds to more than a thousand birds. Cormorants can eat about 1.5 lb. of fish per day. These birds can greatly reduce fish populations and effectively ruin population balance.

Plan ahead and have birds cleared from the pond before fish arrive. To learn more about methods to avoid bird predation, read our fact sheet titled, "Bird Predation On Fish Farms".

Fishing pressure
Improper fish harvest can result in an unbalanced fish population that is no longer able to provide a quality fishery. Over harvest of largemouth bass is a common problem in many small ponds. Largemouth bass are readily caught by knowledgeable anglers. Sufficient largemouth bass may be removed during one fishing trip to "ruin" the pond. An established pond can support harvest of 25-50 small bass (under 12 in.)per acre and any number of bass over 18 inches in length. All bass 12 - 18 in. should be returned to the pond to maintain a growing and balanced largemouth bass population.

When excessive numbers of predator fish like the largemouth bass or channel catfish are removed from a pond, forage fish populations expand. Forage fish such as bluegill will increase in numbers until limited by food supply. The bluegill population will become stunted with few if any fish reaching catchable size. The numerous bluegill eat largemouth bass eggs and their numbers prevent bass from adequately guarding nests. The result is few if any young largemouth bass. The remaining adult bass may grow large but their numbers are very few. The pond will be considered "fished out" by most anglers. Another problem often occurs when no bass are removed from a pond. The population out grows it’s food supply and results in numerous "stunted" bass. Largemouth bass condition can be determined by examining the body of the fish. A rounded plump belly indicates a fish in good condition. A sunken or convex belly or thin fish with large head indicates a fish in poor condition. Bass condition can be improved by increasing fishing pressure on the bass and harvesting all bass caught. Moderate fishing pressure helps maintain a balanced fish population. A few large fish are regularly removed making room for growth of smaller fish; yet not to the extent that forage fish numbers become unmanageable.

Accidental stockings
The ideal balance described above can be affected in many ways. Undesirable fish often enter ponds during heavy rains. This is particularly common with green sunfish and bullhead catfish. Fish move with water currents flowing over spillways, down drainages and even through pastures in less than an inch of water until they enter another pond downstream or upstream from the original source. Such fish migration is the reason spillway screens are recommended on well managed fish ponds. Unscreened ponds allow fish to leave the pond during runoff rains. Expensive fish losses can occur during runoff rains and pond balance can be completely disrupted by incoming and out going fish.

Commonly, undesirable fish enter the pond through different means. A well meaning pond owner or friend may add additional species such as carp, bullhead catfish, green sunfish, flathead catfish or crappie. These fish often upset the aquatic food chain by increasing turbidity of the water or they may directly compete with the desirable species for food and habitat.

Predator / prey interactions
Balance between numbers of forage species and predators is always in flux. Many natural occurrences affect this balance. Complete year classes of fish may be missing if spawning is unsuccessful due to temperature fluctuations, water level changes or predation. Consistently unsuccessful bass spawning can result in a stunted bluegill pond as described above. Insufficient forage fish caused by unsuccessful spawning can result in an excessive bass population made up of many smaller fish and a few large fish in poor condition.

Introductions of undesirable species such as flathead catfish or crappie can dramatically affect largemouth bass populations by reducing forage fish populations and increasing competition for the remaining available food supplies.

Cover
Lack of protective cover can place excessive pressure on forage fish populations, reducing their numbers and upsetting pond balance. Intense predation by largemouth bass may eliminate bluegill from ponds before they reach maturity and spawn. Brush piles and other forms of cover provide protection from predation and help insure that forage fish populations are maintained at an adequate level to support a healthy bass population. In ponds lacking vegetation because of excess numbers of grass carp or because they are very muddy; cedar brush piles can provide protection for forage fish and spawning sites for minnows. Angling results can indicate the need for cover. A turbid or aquatic plant free bluegill / bass pond, that produces very few bluegill and large numbers of 6-11 inch largemouth bass, can benefit from additional cover and a new management

strategy to improve forage fish survival. Fathead and golden shiner minnows will spawn in the brush piles and provide supplemental forage for largemouth bass. Young bluegill also find refuge from bass predation in the brush. Bluegill reproductive survival is improved and a larger forage base is maintained for the bass.

Brush piles also can be used to concentrate fish and improve angling success. Place the piles in 4-10 feet of water to attract forage fish and large sportfish to the pile.

Use concrete blocks or other heavy objects to anchor brush piles to the pond bottom. Mark the location of the brush pile and place it within easy casting distance for convenient fishing.

Climatic conditions
Climatic conditions affect fish populations in several ways. Sudden changes in water temperature caused by cold fronts during spawning periods can disrupt spawning activity or kill fish eggs. Occasional spawning losses due to climatic variation may not disrupt the balance of pond fish populations, however, severe disruptions that regularly occur may limit success of one or more species stocked. Severe disruptions caused by temperature fluctuation are most likely in shallow, wind swept ponds.

Periods of hot, cloudy weather combined with heavy algal blooms can cause reduced dissolved oxygen levels in ponds. Oxygen may drop below levels that sustain many species of fish resulting in large dieoffs; particularly in small ponds or ponds that have received supplemental feeding. Large fish often succumb more readily than small ones during periods of oxygen depletion. Also fish species vary in their tolerance to low dissolved oxygen levels. Pond population balance can be completely altered by these events. Large bass can be entirely eliminated from ponds during periods of low dissolved oxygen. Small bullhead catfish may be the only surviving species in ponds that chronically experience low dissolved oxygen levels due to their ability to tolerate extremely poor water quality conditions.

Watershed changes
Pond water quality is largely determined by what enters the pond from the watershed. As water runs over the soil on its way down the watershed, minerals, nutrients and soil particles are dissolved into the runoff or carried in the flow entering the pond. Carbonates dissolved from limestone determine the alkalinity of the water. In areas lacking carbonate mineral sources, it may be necessary to lime ponds to improve overall health and productivity in the aquatic food chain. Nitrogen (in the form of nitrate) and phosphorous, both important nutrients, also enter the pond through the watershed. Changes in abundance of any of these substances can affect fish populations and this often occurs when changes take place in the watershed.

Plowing or grading the watershed causes erosion. Eroded particles of clay and other soil constituents enter ponds during rains and cause turbidity or "muddy" water. In certain soil types, due to electrical charges on soil particles, the particles remain suspended in the water column causing a permanent increase in water turbidity.

Increases in turbidity affect the entire food chain. Turbidity reduces light penetration. Phytoplankton (microscopic plants), are the basis of the food chain and they require light for the photosynthetic reactions necessary for growth and life. Zooplankton, (microscopic animals), feed on the phytoplankton and provide nourishment for forage fish, larval fish and other aquatic life. The entire food chain becomes disrupted and less productive due to lack of light penetration into the water caused by turbidity increases. Overall productivity in the pond is reduced. The pond is able to support fewer pounds of fish than it could previously.

Increases in turbidity prevent sight feeding fish such as largemouth bass from easily finding their prey. The bass are less successful feeders, they may even lose weight. Soil particles that cause turbidity may settle out and coat fish eggs causing suffocation and death of eggs. All the changes brought about by increased turbidity can alter pond balance and reduce angling potential.

Fish kill resulting from low dissolved oxygen levels
Nutrient increases from the watershed can have dramatic effects on pond balance. Nutrients most often come from, septic systems, livestock, feed lots, poultry houses or fertilizer applications. In urban areas most nutrient pollution results from lawn fertilization. Nitrogen and phosphorous in manures fertilize ponds and cause excessive algal blooms and aquatic plant growth. Spawning areas may become choked with aquatic vegetation. Dissolved oxygen levels are more likely to drop to critical levels for many fish species during periods of hot, cloudy weather due to algal respiration. Heavy plant growth can provide excessive cover for forage fish and reduce bass predation. Forage fish numbers may increase and reduce growth rate of bass. Pond balance shifts in favor of small forage fish and fewer large bass in healthy condition. Nutrient related low dissolved oxygen die-offs can completely alter fish population balance, leaving only low numbers of small fish to repopulate the pond.

A pond balanced to provide fish populations that support a consistently high quality fishery is the desired goal of many pond owners. Pond management goals can be reached and maintained by periodically evaluating the pond, fish populations and watershed changes. Goals are best achieved by avoiding preventable situations and correcting problems before they reduce the quality of the fishery.