How To Assess Your Fish Population
Common Fish Population Problems
Building Your Own Catfish Spawning Boxes
How to Assess Your Fish Population
If you have recently purchased property with a pond and have no idea how it was previously managed or what fish are present, there are two simple ways to find out. Pond owners can sample fish populations by shoreline seining or by keeping track of fish caught, harvested, and released. When a pond is “balanced” there should be 3-5 pounds of bluegill for every one pound of bass. If you are catching only small bass or bluegill, one of the assessment methods below can help diagnose your issues and lead you to the appropriate corrective measure.
Catch/Harvest logs, also known as Angler Diaries, are a great way to assess the quality of fishing and status of the fish population in a pond. It only takes a few minutes to record information from a daily fishing trip that can be used to guide future management of the pond.
The goal of this process is to assess the fishery in your pond as accurately as possible. Accurate and complete data are essential and we recommend completing a record for each angler after each fishing trip. A Catch/Harvest log can be downloaded here
or you can keep similar records on your own.
To assess both the bass and bluegill populations it is necessary to use a variety of types and sizes of lures and baits. Information that needs to be kept includes fish species caught, length of fish caught, whether the fish was harvested or released, and condition of the fish. Other helpful information could include weather, water temperature, and hours fished.
Information on bluegill should only include true bluegills. Hybrid bluegill, green sunfish, warmouth, redear sunfish, longear sunfish, crappie, blue catfish, etc. are to be recorded separately. For help distinguishing different fish species, please reference our Kentucky Fish ID Booklet
Condition of the fish basically refers to the health of the fish. Does the fish appear skinny? If you turn the fish over on its back is the stomach shaped like an ax with a point in the middle or is it rounded and full? Does the head seem disproportionately large compared to the body? This information will tell you if the fish has been getting enough to eat. If not, there is an issue with either food availability or fish health. Records should be kept for several weeks to months depending on how often the pond is fished. A more complete catch/harvest log will make the management process much easier.
Below is an example of what you should look for in your rod-and-reel catch to determine the status of the fish population in your pond.
Balanced Fish Population:
Bluegill of all sizes up to 6 inches and greater and bass of all sizes up to 1-2 pounds (12-15 inches long) and perhaps larger.
No action needed.
Unbalanced: Too many bluegill, too few bass
Many bluegill 3-5 inches long and few bass caught but larger in size (2 pounds or larger)
Solution - remove excess 3-5 inch long bluegill (rod-and-reel, seine, trap), protect all bass by practicing catch and release. Try stocking 50 bass (3-5 in.) per acre for 1 to 2 years.
Unbalanced: Too many bass, too few bluegill
Some bluegill 9 inches or more with few small ones. The bass will be less than 1 pound (12 inches long or less), in poor condition and very numerous. A very small number large bass may be present.
Solution - Remove some bass and harvest all sizes if you desire more quality bass. Do not remove bluegill. If you are managing for a quality bluegill fishery, you can maintain this unbalanced population.
If conditions indicate that smaller bass need to be harvested, the bass size limit may need to be changed to better manage the fishery within the pond. Contact your local Wildlife & Boating officer or your district fishery biologist to check the status of the fish population within the pond. The biologist can then authorize an appropriate size limit or removal of the size limit within the pond until the problem is resolved.
Unbalanced: Small crappie, bullheads, carp or other undesirable fish present
Usually in a stunted population, the fish are small, all about the same size, and may have bulging or very large eyes. Bass and catfish generally have large heads and thin bodies when they are over populated.
Solution - eradicate the existing fish population and restock.
Seining is the use of a net to capture fish and is a quick and easy way to monitor the fish population in a pond. It is most effective in June or July because bass and bluegill have spawned and newly hatched fish have grown large enough to be captured by the seine. A 20 to 30 foot seine that is 4 to 6 feet deep with ¼ inch mesh is most effective. Make three to five hauls in shallow areas (where water depth is less than seine depth). Be sure to keep the weighted line of the seine on the bottom at all times to prevent fish from escaping. Click here
for a video that goes into more detail about seines. Figure 1 illustrates two different seining techniques. After completing each seine haul, record the number and size of fish caught by species. Compare the information you collect to Table 1 to determine the condition of your pond and proceed to the following section for further information.
Common Fish Population Problems
Bass Crowded Ponds
In ponds with too many bass, they compete heavily for available resources. This results in slowed growth rates and mostly small (8-12 inch) bass. If catching large bluegill and redear sunfish is your objective, a bass crowded pond is desirable. If, however, you wish to have a balanced fishery or manage for trophy bass, changes need to be made.
To achieve a balanced fishery it is generally safe to begin by removing 25 small bass per surface acre. The statewide minimum size limit for largemouth bass in Kentucky is 12 inches. Therefore, you will need a Fisheries Management Permit issued by KDFWR to keep bass less than 12 inches. You can get one of these permits by contacting your local Fisheries Biologist. If bass crowding is extensive it may be necessary to remove more than 25 fish per acre. A general guideline is to remove small bass until you do not catch a fish on almost every cast. These bass can be cleaned and eaten or left to feed other animals. Small bass should not be transported off of the property from which they came. Transporting fish from one pond to another can transmit parasites and disease
or affect the fish population in the new stocking location.
To manage for trophy bass you need to completely reverse the status of your bass and bluegill populations. You will need to harvest most of the bass in the pond to attain a very low density of bass. You should remove bass until you only catch a few fish per hour of bass fishing. This will release pressure on the bluegill population and allow it to expand. If bluegill density was very low to begin with, it may be necessary to stock remedial bluegill (3-5 inches) at 100 fish per acre.
Sunfish Crowded Ponds
In ponds with too many sunfish, they are also competing heavily for available resources. Usually in ponds where too many sunfish are present, the number of largemouth bass is low. This results in lots of small, skinny sunfish and a few average to large bass. There are, however, circumstances other than too few bass that may result in sunfish crowding. If a substantial amount of shallow water habitat is covered in aquatic vegetation or an abundance of complex habitat (such as cedar/Christmas trees) bass may not be able to forage effectively enough to control the sunfish population or sustain themselves. This situation can mistakenly seem like bass overcrowding. Bass need to be able to see and then maneuver and capture their prey. Complex habitat and aquatic vegetation limit bass predation on prey species. In this situation vegetation control and/or removal of some amount of complex habitat will allow the bass to effectively feed and control the sunfish population.
If you are interested in managing for a balanced fishery the sunfish population will need to be reduced. This can be accomplished through removal of a minimum of 100 sunfish per acre by angling, shoreline rotenone application in early fall, or stocking 25 remedial bass per acre. See the Pond Renovation section below for more information on selective removal with chemicals. After sunfish removal, stock 25 remedial largemouth bass (6-10 inches) per acre to eat small sunfish.
If you prefer to manage for trophy bass, leave bass density low and harvest some smaller bluegill. As bass grow larger they target the largest prey items they can eat. This results in more efficient energy transfer to growth. A bass will expend more energy feeding if it has to eat many small sunfish to get full as opposed to one or two larger sunfish. While sunfish density needs to remain high, it is also important to have a variety of sizes of sunfish with some larger individuals present.
Undesirable Fish Populations
Nuisance species compete with sportfish for food, cover, and spawning sites. If your pond contains large numbers of undesirable fish species, such as shad, gar, bullheads, carp, suckers, green sunfish, or crappie, the best approach is to renovate and restock the pond at recommended rates. For more information on undesirable fish populations, see the Stocking and Harvesting
Often, when nuisance species or an unbalanced fish population is present, the best solution is to eliminate the resident fish and restock with a desirable combination at recommended rates. Consult your District Fisheries Biologist to determine if complete renovation is necessary.
The best method for renovating a pond is to drain and completely dry the pond. This lets you modify pond depth, add/remove structure, lime, or put in a water control structure, among other things. This method is especially enticing for pond owners with access to heavy equipment. While dry, shallow shoreline areas may be deepened and set to the recommended slope (3:1). This will help limit aquatic vegetation growth and reduce the extent of thermal stratification. An important thing to remember is that if all water cannot be removed from the lake basin you will need to poison the remaining pools to ensure all fish are eradicated. Small fish can survive in very little water for a long period of time. If these fish persist until the pond re-fills your renovation may be ruined.
If the water cannot be completely removed or if a small amount remains in the lake basin, the next step is to apply an approved fish toxicant to eradicate the remaining fish. Rotenone is a restricted use chemical and may only be purchased and used by someone with a current Kentucky Pesticide Applicator’s License. Rotenone kills fish by disrupting the fish’s ability to use dissolved oxygen. In response to the rotenone, fish move to the water’s surface and gasp for oxygen as if the water was oxygen-depleted. However, rotenone does not reduce the amount of dissolved oxygen in the pond water. Rotenone may not be applied to, or allowed to enter public waters. A land owner may be held liable if fish are killed in adjacent, non-target waters.
Except for swine, which are sensitive to rotenone, livestock can drink water from a treated pond. As a precaution, it is best to wait a few days before giving livestock and pets access to the treated water. Human swimming and wading may resume three days after treatment. Crops should not be irrigated with treated water until the recommended detoxification time period has elapsed.
Selected Use and Application Rate
Rotenone has two main uses in small lakes and ponds. The first is to remove all fish species before restocking desired species. The second use of rotenone is to “selectively” remove unwanted fish from the pond’s fish community. This method generally involves the removal of rotenone sensitive species such as grass carp and shad but may also be used to remove excess sunfish from shoreline habitats. To do this the rotenone treatment must be adjusted to a lower concentration that will affect only sensitive species. It should be noted, however, that this method has a higher associated risk, with the potential to eliminate some non-target species. This method is generally not recommended for first time applicators.
Rotenone will remove fish only if the correct concentration in applied. The first step in calculating the proper amount of chemical to apply is to determine the pond surface acreage and average depth. These figures must be as accurate as possible to maximize results. Please reference this page
for assistance with these measurements.
The application rate for liquid rotenone is 0.1 to 5.0 mg/L for the 5% active ingredient formulation. Concentrations of 1 to 3 mg/L are used to remove most fish populations. Higher concentrations are needed when treating a pond with less sensitive fish species such as bullhead catfish and common carp. Refer to Table 2 for a Guide to Application Rates. Liquid rotenone should be diluted in water at a ratio of 10:1 before application. For normal pond use (1 mg/L) 1 gallon of 5% liquid rotenone will treat 3 acre-feet of water.
Rotenone toxicity increases with increasing water temperature. However, in warm water the chemical breaks down rapidly and may not kill all fish present before it dissipates. It is most effective when water is cool (45 to 75°F), free of aquatic plants and dense algal blooms, and has low dissolved oxygen, low turbidity, and low alkalinity. Because rotenone is more toxic to fish than fish eggs, the most effective time to apply the chemical is in early fall after all pond fish have completed spawning. Fish can detect rotenone in the water and try to escape exposure. Be sure to spray the chemical first around the shallow waters of the shoreline to eliminate habitat for fish to take refuge. Any chemical tank and pressure sprayer will work well in shallow water. Use a weighted line from a boat or drip/pour directly into the prop wash of the motor to apply the chemical to deeper water. Care should be taken to apply evenly throughout the pond. Be sure to avoid direct contact with the chemical and wear proper safety equipment listed on the product label when handing and applying this chemical.
Rotenone will detoxify in 1-4 weeks depending on rate of application and water temperature. Refer to Table 3 for more information on the detoxification time period. The water can be tested for toxicity by placing fathead minnows in a minnow bucket suspended at the pond surface. If the minnows survive for 48 hours the pond is ready for restocking.
Animals, including fish, need a healthy environment, or habitat in order to survive, grow, and reproduce. Fish populations can be directly affected by the quality and quantity of fish habitat in their living space or water body. Structure in a pond serves as habitat for fish in two regards. Fish are drawn to the structure for feeding and protection. The structure helps support the basic elements of the aquatic food chain. Structures provide substrate for algae and small aquatic insects. These small plants and animals will be a potential food source for small fish, such as bluegill and fingerling size bass, which will be a potential food source for larger predator fish, such as bass and catfish. Therefore the structure also acts as a fish attractor, drawing larger fish to its proximity. With the larger fish concentrated in one area, angler success should increase.
Fish habitat can come in many forms and can be most anything in the water body that fish can gather around. The most natural form of habitat is aquatic vegetation. There are many types of aquatic vegetation and they may show up naturally or be planted by the pond owner. Although aquatic vegetation is beneficial, it is often hard to manage and where a little vegetation is a good thing, too much can become a problem. A simpler approach is to use natural or man-made materials as fish habitat. The most common things used for fish habitat are tree tops, Christmas trees, stumps, wooden pallets, and other manmade, artificial structures. The Southern Division of the American Fisheries Society (SDAFS) has a great online manual
that describes and diagrams different types of structures various agencies have used and continue to use in state-owned water bodies.
Creating fish habitat with wooden pallets (Photo by Neal Jackson)
Plastic barrels used as fish habitat (Photo by Paul Rister)
Adding brush piles for fish habitat (Photo by Paul Rister)
Artificial habitat added to pond after filled with water (Photo by Neal Jackson)
The easiest time to add habitat is after digging a pond but before it is filled with water. If trees are cleared from the land during pond construction, stumps or logs can be pushed back out into the pond upon completion. These structures will often not need to be anchored. However, if you are adding structure after the pond is full of water, then it will likely need to be anchored down with concrete blocks.
Stumps pushed back into pond after construction (Photo by Paul Rister)
The ideal amount of habitat to add to a pond is about 20% of the surface acreage. Habitat should be placed within casting distance from the shoreline, but avoided in areas where swimming might take place. The ideal water depth to place the structure in will range from about 4 feet to 10 feet. Structure in deep water will likely be unused during the summer months as water in deeper areas of the pond will become devoid of dissolved oxygen. Although structure could be added to the existing pond throughout the year, fall and winter are better times to complete this work.
There are a few circumstances where the fishery in your pond might not benefit from the addition of structure. If the fishery is overpopulated with small sunfish, the addition of habitat will only allow more protection to the small fish. Ponds overpopulated with stunted forage fish might produce a few trophy bass but will not yield quality bluegill or consistent bass fishing. Likewise, if the existing pond has a dense coverage of aquatic vegetation, no additional habitat should be added until the vegetation is controlled. Excessive vegetation can also lead to an over-abundance of small forage fish as it will hinder the ability of bass to capture them.
In order for your fishery to sustain itself without having to be re-stocked every year, the fish will need to spawn. Without the right type of spawning habitat, the bass and bluegill could have very limited or unsuccessful spawns. A soft, muddy or silty pond bottom is not the preferred spawning habitat for these fish. Bass and bluegill like to move into shallow water during the spring time for spawning. They will attempt to create a spawning bed by using their tail fin to fan away the loose silt. This action exposes more firm substrate and rootlets of submerged grass or aquatic vegetation. The fish will create a depression and lay their eggs in the cleaned out site. Once the eggs are laid, it is up to the male fish to guard the nest for a few days as the eggs develop into fish (fry).
There are spawning substrates that can be added for fish to spawn on, such as sand or small gravel. These materials can be added to a pond during construction or after it is full of water. A spawning area can be created by placing small pea-gravel in an area adjacent to the shoreline. Ideally water depth would be about 12 to 24 inches, but fish can spawn shallower or deeper if necessary. The bed of gravel needs to be several (3-6) inches thick. The ground in these sites needs to be somewhat level or only sloping slightly. Bluegill will typically spawn in colonies, and their beds will be very close together. Spreading the gravel out in one large area will suffice for bluegill. However, spawning beds for bass might be spread out as much as twenty to twenty-five feet apart in order to avoid predation.
Bluegill spawning beds
Individual spawning beds can also be created in the pond. These beds can be made by cutting the top or bottom out of a 55 gallon plastic drum. A short side should be left on the lid so that it can hold a few inches of gravel. These nesting sites could then be placed around the pond in about 24 inches of water. For bluegill they can be close together while for bass it is best to spread them out.
Individual spawning beds used by bass and/or bluegill. Notice the overhead cover provided by this design.
Individual spawning beds used by bass and/or bluegill. Sides were left on this structure to help lower it into the lake from a boat.
Typically channel catfish do not spawn in a pond unless you provide them with the desired spawning habitat. Catfish want to back into a cavity or overhang to spawn. Inside the cavity, they can lay their eggs and the male can protect the nest. The male catfish will then only have to guard one opening from potential predators, such as bluegill and small bass that like to eat catfish eggs or fry as they move off the nest.
There are many types of structures that could be added to the pond to create spawning habitat for catfish. Some suggestions include, a section of large diameter sewer pipe, a five-gallon bucket or 55-gallon drum turned on its side, stacks of concrete blocks, an old style milk can, or wooden box with only one opening. The structure should be big enough that both the male and female catfish can fit inside in order to spawn. The structure should be placed in about 5 feet of water with its opening pointing away from the shoreline.
Channel catfish spawning structures
Wooden catfish spawning box
Feeding your fish has the potential to increase the production of the pond, allowing for higher stocking densities and faster growth. Feeding fish is particularly beneficial in ponds where the production of natural food is limited by low nutrients or other water quality problems. There are two basic foods to consider, based on which species you are trying to help. Pelletized floating fish food and small forage fish are the two common forms of supplemental feeding.
For catfish and bluegill, a floating pelletized fish food is best. Some pond owners choose to use dog food. The fish will feed on the dog food; however the optimal growth seen with a higher protein feed designed for fish will not be achieved. When choosing the size or diameter of fish food to use, the size of fish should be considered. Small fingerling size catfish may not benefit from a larger size fish food designed for adult catfish.
The best time to feed the fish with pelletized fish food is during the morning in the summer and during the late afternoon in the spring and fall. During the winter months fish feed less, but might take some food on warm sunny days. To keep feed from blowing around on the surface of the water, you can make a feeding ring. A feeding ring can be made from PVC pipe or plastic water line. The idea is to create a floating ring or square. The size of the feeding ring should be about 8 to 10 feet in diameter. The ring can be tied off to a dock or shoreline and should be away from the shoreline, but close enough that you can throw the food into the ring. The amount of time it takes for fish to consume feed is the best measure of how much food to feed daily. You want the fish to eat all feed in about 10-15 minutes. If feed is left floating after 15 minutes, then you likely fed too much. If they clean up the feed in less than 10 minutes you may not have fed enough.
There are a few negative effects of supplemental feeding pond owners should be aware of. Decomposing fish food will lower oxygen levels in the pond. During the summer months, when dissolved oxygen levels are already low in the pond, feeding fish excessively can lead to oxygen depletion and ultimately a fish kill. In the event that the fish are not eating all feed during the summer months, reduce the amount or wait a few days between feedings. Aeration will help increase dissolved oxygen levels in the pond and usually only needs to operate for a few hours first thing in the morning. A second problem with feeding is that you increase fish biomass beyond the carrying capacity of the pond. As fish grow, space becomes more limited. One way to think about this is that a one acre pond might be capable of sustaining 100 one-pound channel catfish, but not 100 five-pound catfish. So as you feed the fish, and their size increases, you will need to harvest some of your catfish.
For feeding largemouth bass, the recommendation is to stock more forage fish. In a typical pond, the forage component is made up of small bluegill. However, there may be times that the population of small bluegill in the pond becomes depleted. This may be due to overcrowding of bass or poor spawning of bluegill. Instead of buying the more expensive bluegill to feed your bass, you can stock fathead minnows, also called a tuffy. These minnows are different than a shiner minnow purchased from a bait shop. Shiners should be avoided because they can take over a pond by growing to a size that is not suitable for bass consumption. Fathead minnows are fast growing, but normally only reach three inches in length. When you purchase fathead minnows, you will be buying them by the pound. Typically there are 200 to 350 fathead minnows per pound, depending on their size.
Fathead minnows will reproduce in a pond. Minnows spawn by attaching their eggs to the underside of a rock or piece of wood. Wooden pallets make Ideal spawning habitat for minnows. Several pallets stacked in shallow water will provide suitable spawning substrate for the minnows.
There is some debate about the best time to stock minnows. Some suggest stocking them into a pond before adding other fish. However, having minnows in the pond prior to stocking fingerling bluegill and largemouth bass will not benefit the pond. In fact, it may slow the initial growth of your sport fish because all small fish are feeding on the same food source, the plankton. Minnows should only be stocked after your bass population has been in the pond for a few years. Remember that in most situations minnows will not become established and only provide a one-time feeding “bonus” for the bass. Most ponds managed for a balanced population will never need supplemental forage.