Why Fish?

PK Gills AquaticsWith the right expertise, fish are a cost-effective way to manage many of the nuisance problems associated with lakes, ponds, and canals. Using the natural biological systems and the food chain you can impact nuisance algae, weeds, and insects in most water bodies. In one Irrigation District the company’s program saved hundreds of thousands of dollars and freed them from dependency on harsh toxic chemicals. The savings on the District’s insurance alone made the program worthwhile.

In the United States there are an estimated 5 million private lakes and pond. Many are built for irrigation or livestock watering but recreation and enjoyment of the aquatic environment are more dominant reasons. Whether we are speaking about a residential lake community, golf course lake, industrial pond, irrigation canal, urban lake, water ski park, or wildlife preserve, no two lakes are alike, nor are the climatic zones or catchment area in which they exist. Therefore, management techniques vary widely, yet the basic principles remain the same.

All water bodies exist as living biological systems. Respiration and photosynthesis are continually cycling. Nutrients (mostly carbon, nitrogen and phosphorus) wash into the lake from the surrounding catchment area and are digested. Sunlight drives the process via photosynthesis in algae and plants while wind serves to mix a lake from top to bottom and add oxygen. If left alone in the wild these biological processes normally remain in balance for extended time periods. In more populated areas lakes are often overburden with added nutrients (such as fertilizer or street runoff) and the natural process is thrown out of balance. This may also occur in places where livestock are grazing in or near lakes and streams. The extra nutrients may be converted into an abundance of algae or weeds that can degrade the system. Oxygen can become depleted killing fish and sending the lake into a smelly, unsightly eutrophic state.

thefoodwebA good example of how the cycle works can be seen in this food chain drawing or by visiting a local wetlands project. Many wetlands are now being established to enhance municipal sewage treatment. The City of Avondale near Phoenix, Arizona and San Diego, California both use wetland principals to treat sewage. Water with a high nutrient load is passed into a wetland area. The nutrients are slowly digested and converted into plant material such as water hyacinth, bulrush or algae. Algae are then eaten by zooplankton. Zooplankton is consumed by herbivorous fish, which are consumed by larger predator fish or eaten by birds. The wetlands attract a variety of wildlife all participating in the food chain or nutrient cycle. As the water passes through the system, nutrients are converted or used up. The water gradually clears and regains a satisfactory oxygen level. Oxygen supports bacteria that assist with decaying organic material while allowing fish to breathe.

Many water bodies cannot keep up with the nutrient loading and require intervention. All such programs begin with the stakeholder’s objectives and budget. Often such projects require multiple interventions such as;

Decreasing the nutrient loading from the catchment area. This may require education and awareness of those who farm in the area, wash their cars in the street or apply fertilizers near the lake. Many mitigating activities are possible.

Aerating the lake
Increasing the oxygen levels and de-stratifying the water column or mixing the warm and cold layers is one of the best things that can be done for an ailing lake. The added oxygen promotes all biological processes and fish health.


Mechanical harvesting
Submerged and emergent weeds can be cut, pulled or dredged. This is an expensive and generally short-term solution. Further complicating the problem are weed species that spread by fragmentation. However, this can be a viable alternative in some situations.


Chemical applications
Although not our first choice, chemical intervention can be desirable for quick results. Natural processes take longer and produce more cost-effective long-term solutions. However, there are instances when chemicals offer a practical alternative.


Dye the Lake
Organic colorants restrict sunlight penetration into a lake and can reduce algae and aquatic weed growth. Intentionally fertilizing ponds to produce light blocking phytoplankton is a method used in some management plans. Dye is generally inexpensive and safe.


Stock the correct fish
To address specific problems and build a food web that digests the nutrients naturally. With good expertise this method is safe, effective and less costly.


Harvest the lake
Once the nutrients have been converted to fish flesh, for example, it is necessary to periodically remove them from the system. Fishing pressure and bird predation may remove enough, but often the pond owner is not in control of the fishing pressure. Continued stocking to vary the age class of the fish population may also be necessary.

At P.K. Gills we have experience in multiple interventions and specialize in using fish. We listen, gather information and respond to the needs of the stakeholders by developing and executing comprehensive stocking and maintenance programs. We could carry on about the nitrogen cycle or lake chemistry and all the variables that can impact on the health of a lake, but such scientific discussions won’t interest everyone and are available in many online sites.