Using Fish and Bacteria for Controlling Algae

Notes on the Complementary Effects of Using Fish and

Beneficial Microorganisms for Controlling Pond Algae

by Ronald Pifer


B.S. Mechanical Engineering, Duke University

M.A. Environmental Biology, University of Colorado

Society of Sigma Xi, Scientific Honor Society                          

My previous article, published in August of 1998, focused on “Ecological Controls for Healthy Ponds.” This approach stressed the advantages of employing multiple management tools to reduce costs and to minimize environmental damage. These tools included: (1) restricting nutrients entering the pond; (2) using biological controls, such as fish and beneficial bacteria; (3) using aeration systems, such as fountains, blowers, diffusers, and water falls; (4) using aquatic sun screens; and/or 5) physically removing filamentous or rooted algae, whenever possible.

In this update, we will focus on biological controls and show how they can help one another, to produce a more powerful and effective, algae-control program. This approach utilizes a subtle synergism, or cooperation, among control species. It is possible because the strength of one organism can often offset, or complement, the weakness of another. Thus, the combination produces stronger and more desirable results than are possible with individual controls, acting by themselves.

The fishery controls usually entail the use of grass carp, or white amur, because of their ability to gradually control many rooted aquatics. Other fish are sometimes used to control the microscopic algae, or phytoplankton. They include tilapia and Israeli carp, and in some cases, gold fish. However, it is the grass carp that are the most wide-spread, algae-control fish, and it is this species that can be used most effectively with the introduced pond bacteria.

Grass carp are beneficial because they are known to favor American elodea, hydrilla, naiad, and muskgrass, or chara. They have moderate inclination for duckweed, pond weeds, bladderwort, fanwort, coontail, water pennywort, and water primrose. Part of their downside is that they do not care for water lily, sedges, cattails, water meal, and water hyacinth (Georgia Cooperative Extension Service).

On the other hand, beneficial pond bacteria are more effective in controlling the floating, filamentous algae and the microscopic, suspended algae, which the grass carp don’t like or cannot eat. The downside of the beneficial bacteria is that they are less effective in controlling those rooted aquatics that the grass carp prefer. Therefore, in terms of preferences or weaknesses, the grass carp and the beneficial bacteria can complement each other very nicely.

When grass carp are stocked properly in a pond, their feeding activities will generate a multitude of plant by-products, which natural pond bacteria will turn into nitrates and phosphates. These nutrients will eventually cause a phytoplankton bloom, resulting in green or blue-green water (University of Florida, 1998). Once this happens, the stage is set for a phytoplankton “crash,” or massive die-off.  At this point, the native pond bacteria work “overtime” to degrade the extra dead algae, resulting in lowered oxygen levels and, sometimes) bad odors. As yon know, this condition often leads to stressed fish and, possibly, to fish moralities.

Fortunately, the laboratory-cultured, beneficial bacteria have been designed to alleviate this situation by consuming those nutrients that are released by carp and processed by native pond bacteria. They also can improve the bottom environment by taking over the decay process from anaerobic bacteria, and thus, they can eliminate bad odors and improve public relations.

Their success is dependent on several factors, however. First) the bacterial formula must contain those species of bacteria that consume nitrates, turning them into nitrogen gas, which is harmless and represents about 80% of the air we breathe. Secondly, the bacteria must be able to bind up the phosphates and render them unavailable as plant nutrients. Thirdly, the formula should contain facultative aerobic bacteria, which can operate with or without oxygen. Fourthly, the formula must contain sufficient concentrations to be effective. And finally, the cultured bacteria must be suited to the pond’s environment, with regard to its temperature and pH.

Another benefit of the beneficial microorganisms is their ability to have a positive impact on the control of the filamentous algae. This type of plant grows upward from the bottom and spreads into stringy mats on the surface. If not attended to, it can rot and cause odor and visual problems. The grass carp, on the other hand, do not particularly care for this common type of pond algae. Chuck Cichra of the University of Florida (1998) stated that he has seldom noticed grass carp feeding on this type of plant. Only once did he see it happen, when a lone, large carp had eaten every other plant out of a small farm pond and was left to either starve or eat the filamentous algae. Gee, I wonder what it did!

In conclusion, several points should be taken into account when considering how to best manage these biological controls. First, if you are allowed to use grass carp, you need to determine the proper stocking rate and size for your conditions. Secondly, you need to determine the proper bacterial formula and the treatment timing. And thirdly, you need to realize that biological results are gradual, compared with poisons, yet their long-term benefits are favorable for the environment, are usually more affordable, and are good for public relations…

If you would like any help or assistance in implementing these strategies, please do not hesitate to contact me.  A knowledgeable and cooperative partnership makes both players stronger and their joint efforts more powerful.


Mr. Pifer has spent over 45 years in Ecological Consulting; including 7 years in Aquaculture R & D; 15 years in environmental impact assessments; 15 years teaching science at the junior high, high school, and college levels; and over 20 years in the Bacterial Products Industry. He may be reached at: Environmental Solutions, P.O. Box 714, Stevensville, MT 59870, U.S.A.; or thru the web at ; or by email at; or by phone at 406-777-4990.