Pond and Fish Ecology
A basic understanding of the biology of fishes and their interactions with their environment is helpful in understanding how to manage fish. Knowledge is useful in all aspects of pond management from initial pond construction to salvaging a problem pond. The basic needs of fishes are (1) food; (2) good quality water; (3) shelter; and (4) a spawning area. The first two items are generally the most critical, but all are important to varying degrees at some time. Each of these items will be briefly discussed to give the reader a basic understanding of the reasons for management recommendations contained on this site.
The natural foods of fishes are either produced in the pond or are washed or fall into the pond from the surrounding area. Food produced in the pond has its origin in the nutrients that are dissolved in the water and in the pond bottom. A variety of plants utilize these nutrients to grow. These plants may be microscopic algae that give a green color to the water or they may be large rooted plants that grow in shallow water areas. Plant material in turn is food for a variety of small animals such as insects and microscopic zooplankton. These small animals are eaten by fish such as bluegills and young bass. Large fish like the bass will feed mainly on small fish, crayfish, and tadpoles. The chain of events leading to the production of large fish can follow different routes. It can follow a “food chain” from nutrients, to algae, to zooplankton, to small fish, to large fish, or it can go from nutrients, to rooted plants, to insects, to small fish, or large fish. In reality, food chains have more links or steps than mentioned here and there are considerable crossing over between the various chains. What really exists is a “food web.”
All ponds contain nutrients, which ultimately produce food for fish. The amount of nutrients present depends upon the productivity of the watershed. The amount of fish that the pond can support is called the “carrying capacity.” This is comparable to a pasture’s capacity to support only a certain amount of cattle or a garden’s ability to produce only a certain amount of vegetables. In Kansas, mixed species ponds typically support between 100 and 400 pounds of fish per acre if supplemental feeding is not provided. The average pond supports about 250 pounds of fish per acre. Populations can comprise many small individuals or fewer large individuals, but the total weight of fish will depend upon what the pond can support. The amount of fish food a pond will produce is limited by the amount of nutrients and will be shared by the existing fish community. By managing for fewer fish, larger fish can be produced.
Fish require good quality water to survive, grow, and reproduce. Good quality water is free of pollutants such as toxic materials, excessive organic matter, and silt. Water should also have high oxygen content. Oxygen deficiency is a common water quality problem encountered in ponds. Most fish species require at least 5 parts per million (ppm) of dissolved oxygen for good health and vigorous growth. They can tolerate 1 or 2 ppm for short periods, but they will become stressed, will cease feeding, and may become susceptible to diseases.
The amount of oxygen contained in the pond depends upon the water temperature and the depth. During late winter and early spring, the water in a pond will have the same temperature from top to bottom. In late spring, increased atmospheric temperatures begin warming the pond from the surface down. Water in shallow ponds located in open areas exposed to the wind may continue to mix through ice-free periods, but by the summer the surface water in deeper, less windswept ponds is considerably warmer (and much lighter) than the bottom water, so a thermal stratification occurs. This is a fairly stable condition with the warm upper layer (epilimnion) floating on the cool bottom layer (hypolimnion) separated by the transition zone (thermocline). As the wind blows, only the upper layer is mixed and oxygenated. The lower layer does not receive additional oxygen and in fact slowly loses its oxygen by the decay of organic matter on the bottom. By mid-summer oxygen is consumed in the lower layer so fish are confined to the upper layer and thermocline. This is why ponds built deeper than 15 feet waste space during the summer. On the other hand, a pond that is too shallow (less than 10 feet deep) may encounter summer-kill problems. This topic is discussed further in the “ Fish Kills” section.
In late summer and fall, the surface water cools until its density is similar to the bottom water. Strong winds are then able to mix the water from top to bottom. This carries oxygenated water to the bottom and fish are again able to inhabit the entire pond.
After ice forms in the winter, water on the bottom of the pond is slightly warmer than water just under the ice. Fish usually prefer to locate near the bottom for this reason. Since ice prevents a mixing action from occurring, organic wastes again settle to the bottom, much as occurs during the summer. Decomposition of organic wastes uses oxygen, and excessive decomposition can drive fish off the bottom, up the water column, in search of oxygen. Severe cases of decomposition in combination with lack of oxygen production by plants results in an oxygen deficiency throughout the pond and eventually winterkill. Particulars on this subject are discussed in the “ Fish Kills” section.
Fishes are eaten by a great variety of mammals, birds, reptiles, amphibians, other fishes, and even invertebrates (some insects eat small fish). In order to survive, fishes have evolved various behavior patterns. Pond fishes always try to hide when danger threatens. They can hide by swimming to deeper water or by moving behind a rock, stump, brush, or plant. In a pond, fish communities will exist without physical structure, but fish are sure to concentrate near a structure if it is present. In fishing ponds, structures benefit fishermen more than the fish since anglers know the most productive areas for angling are near areas with habitat structure. This is why the addition of fish attractors is recommended in all but catfish-only ponds.
Some species of fish require specific bottom material to reproduce. Largemouth bass and bluegill are generalists and will spawn on about any type of bottom material, but the channel catfish is more particular. It requires some type of cavity such as a hole in the bank or solid structure in the form of a stump or rock for nest establishment. As stated several times previously, catfish reproduction is not desired in catfish-only ponds, so nesting structures should not be provided.
When species other than bass, bluegill, and catfish are desired in a pond, it is necessary to know their reproductive requirements in order to determine whether they will be able to maintain a population.
Many fish species can be found in Kansas ponds, but only a few lend themselves to effective management for sport fishing purposes. The most common species stocked in ponds are the largemouth bass, bluegill, and channel catfish. Other species that can be used for specific management objectives include fathead minnows, crappie, black bullhead, redear sunfish, and gizzard shad. Green sunfish and carp are also often found in ponds. A brief description of these species’ life histories and some information on additional species follows.
The largemouth bass is a large predatory fish that belongs to the sunfish family. It is one of three kinds of black bass found in Kansas, the others being the smallmouth and spotted or Kentucky bass. The largemouth is greenish colored on the back with a white belly and a dark band along its side. Its mouth is large with the upper jaw extending beyond the eye when the mouth is closed. This feature and coloration set the largemouth apart from the other two basses. This fish will eat anything it can get into its mouth. Common food items include insects, crayfish, frogs, and small fish. In the southern United States, largemouth bass commonly attain weights of over 10 pounds, but anything over 7 pounds is considered a trophy in Kansas. Largemouth will spawn after reaching a size of about 10 inches. This usually corresponds to an age of one or two years. Spawning occurs during spring when water temperatures reach 60-70°F. The male makes a large saucer-shaped nest on the bottom in shallow water by fanning an area free of debris with his tail. The female deposits eggs in the nest, and the male fertilizes them. The male protects the eggs as best he can from predation and maintains good water quality by fanning with his tail. If the male bass is removed, the eggs will die. He guards the eggs until they hatch and the young are large enough to swim and find food. This takes about 1-2 weeks.
The bluegill is a deep-bodied sunfish with a small mouth. With an increase in size, the fish changes from a silver lavender color to greenish brown, with an orange or yellow breast. All sizes of bluegills possess a blue-black gill cover flap. Bluegills feed primarily on insects. Bluegills typically mature at a length of 3-5 inches. They should reach a length of 6-8 inches, but larger fish can be produced if properly managed. Fingerling bluegills stocked in the fall will spawn the next summer. Bluegills spawn from May to the beginning of September with a peak in June. The male makes a saucer-shaped nest on the bottom in shallow water like the bass and guards the eggs and young. The bluegill’s ability to spawn so prolifically makes it a good food fish for bass.
The channel catfish is a native stream fish with a deeply forked tail, gray back, white belly, and 8 barbels around the mouth. Young fish have some black spots, but these are lost with maturity. The channel catfish’s diet consists mainly of invertebrates and small fish. Channels grow rapidly if enough food is available and often exceed 5 pounds. They spawn in early summer when the water temperature reaches 70-75°F. The male makes a nest in a hole in the bank, under a log, or next to any material that will provide protection for the young. The male also guards the eggs and young fish. Male channel catfish develop a bluish color, which often causes them to be misidentified as blue catfish. The anal fin of a blue catfish has 30 or more rays while channel catfish have 24-29 rays.
The fathead minnow is a common baitfish and is also stocked in ponds to accelerate initial bass growth rates. It is a dull silvery color and reaches a length of 2-3 inches. Fatheads feed on small invertebrates and plant material and are hardy and prolific spawners. Spawning occurs all summer. Eggs are deposited on rocks or other objects.
The gizzard shad is a member of the herring family. It is silvery colored and has a sharp, saw-like ridge on its belly. It is the primary food for large predatory fishes in large reservoirs. It feeds on microscopic plants and animals and can produce high numbers of young. Shad spawn from spring to summer by randomly scattering eggs in shallow water.
There are two kinds of crappie, the black and the white. The black crappie prefers clear water and has seven to eight dorsal spines and black spots scattered randomly over its body. The white crappie is slimmer than the black, has five or six dorsal spines, and its spots tend to form vertical bars on it sides. In turbid water, white crappie usually predominate. Both kinds feed on invertebrates and small fish. Their reproduction is similar to that of the bass and bluegill. The minimum length at maturity is 6-7 inches. They tend to overpopulate if there is not enough predation on the young. In combination with larger numbers of bass, they grow rapidly and often reach lengths of 10-12 inches.
The green sunfish is often incorrectly called a perch. It is a member of the sunfish family along with the black basses, bluegill, and crappie. It is greenish in color and has a mediumsized mouth. It feeds on a variety of small animals and seldom grows over 6-7 inches in length. Green sunfish are common in small streams and often get into ponds by swimming over spillways. They can be a nuisance in a pond if bass are not abundant. Green sunfish reproduction is similar to that of bass and bluegill.
The redear or “shellcracker” sunfish is a native of the southern United States. It has been stocked in place of or in combination with bluegills because it grows larger than the bluegill and does not have a high reproductive potential. Redear do not typically overpopulate like other sunfish and, in fact, do not provide enough prey for largemouth bass. Use of redear as only a sport fish in combination with largemouth bass works well as long as bluegills are also present to serve as the primary prey. A mixed stocking of two-thirds bluegills and one-third redear can add variety to a pond. Redear feed primarily on bottom organisms, particularly snails, and require clear, deep water with abundant aquatic vegetation. Their commercial availability in Kansas is limited.
The three sunfishes previously described, along with some others, have all been hybridized with each other in an effort to produce offspring that do not overpopulate, grow larger than either species, and are easy to catch. Hybrid sunfish fill these requirements, but parental species (consisting of only males of one species and only females of the other) need to be stocked about every 4-5 years to maintain hybrid population numbers. Hybrid sunfish also provide too little prey to support desirable largemouth bass populations.
This bullhead is a common catfish of small sluggish streams. Its back is gray or black, and its belly is yellow or white. The tail is not forked but slightly indented. It feeds on a variety of small animals and seldom gets over 15 inches long. Bullheads often gain access to a pond by swimming over the spillway. This species quickly becomes overpopulated if the pond is muddy or low on bass numbers. Reproduction is similar to that of the channel catfish. After hatching, young bullheads will travel in a compact school accompanied by one or more adults.
The carp is a large member of the minnow family. It feeds on bottom organisms and tends to stir up the mud and is thus undesirable in ponds if sight-feeding fish are desired. Carp usually get into ponds when they are seined from creeks for bait and released or lost in the impoundment. A well-established bass population will control this species, but overpopulation problems can result if the pond is already muddy or few bass are present.
Northern pike, walleye, flathead catfish, and trout are desired by some pond owners. While they do not cause problems in ponds, they are not particularly well suited to the pond environment. They do not reproduce adequately in ponds to maintain their own numbers; they are costly to stock, difficult to obtain, and a pond cannot support many of them. Northern pike and walleye may be part of the stocking combination in large watershed structures as long as the owner realizes that he will probably need to supplementally stock them every few years to maintain them in his impoundment. Walleye should not be stocked where bluegills are the only prey fish. Gizzard shad should be present if walleye are desired. The flathead catfish is often stocked into ponds as a trophy or predator fish. While the flathead eats primarily fish, it will not control bluegills as well as a properly managed largemouth bass population. Flatheads should therefore not be stocked in place of bass. Few Kansas ponds are capable of supporting trout yearround. Trout require water temperatures below 70°F along with a high oxygen content. These conditions do not occur simultaneously in most Kansas ponds during summer months.
Organisms released into habitats where they are not native often out-compete natives through a lack of predators, parasites, and competitors that kept the non-natives in check where they originated. In favorable environments their numbers can explode, and, once established, are seldom eradicated. Some aquatic nuisance species in Kansas are the asian carp, zebra mussels, and white perch
Anglers can help prevent the spread of ANS species by monitoring their boats (including pond bass boats, canoes, float tubes), trailers, anchors, and anything else that comes in contact with the water. Remove any plants or animals from boating equipment and drain the livewell before leaving the water body. Empty bait buckets on land — not into the water — before leaving the waterbody. Wash boating equipment with hot (at least 104°F) water and dry for at least 5 days before transporting to another waterbody. Learn to recognize exotics that may be in or near your area. Consult the Department of Wildlife, Parks & Tourism for more information.
In southern United States reservoirs this genetic strain of largemouth bass has produced record-sized fish. Pond results have not been as productive. Florida-strain largemouth bass are less temperature tolerant than our native, northern-strain largemouth. Since temperature effects in ponds can occur quicker and last longer, the effect of winter temperatures can wipe out a pond owner’s attemp to produce trophy Floridastrain largemouth bass. It is much more productive to stock northern-strain largemouth bass and manage your pond for big bass as specified later in this booklet.