Can I Stock Tilapia or Other Fish in My Pond to Control Algae and Plants?

The most common problem reported by Pennsylvania pond owners is nuisance growth of aquatic plants and algae. There are various approaches to control plants and algae including reducing nutrients, dredging, mechanical harvesting, or chemical herbicides (all explained in Management of Aquatic Plants) but may pond owners seek more "natural" approaches. Various fish species have been marketed as potential biological options to consume unwanted algae and plants but, most recently, the internet has proliferated the idea of stocking tilapia in Pennsylvania ponds – especially for algae control.

Tilapia are a tropical fish from Africa that spawn and grow rapidly in ponds with very warm water. They feed almost exclusively on large amounts of algae and aquatic plants. They have also become a popular consumable fish because of their mild-tasting flesh, low cost, and widespread availability in grocery stores.

Although tilapia can be raised in controlled and enclosed aquaculture facilities for restaurants and grocery stores, it is illegal to stock tilapia into earthen ponds in Pennsylvania. Non-native fish like tilapia are illegal to stock for algae control because they could escape and cause damage in natural streams and lakes by carrying diseases and out-competing native species like bass and sunfish.

Good alternative fish to stock in earthen ponds that can help to consume some aquatic plants and algae include channel catfish, white suckers, golden shiners, or fathead minnows. In cases of severe overgrowth of algae or plants, these fish will not provide complete control and would need to be used in conjunction with other control methods mentioned above. Other fish species like bullhead catfish, koi, and common carp are not recommended because they are prone to overpopulation and muddying pond water in search of food. Koi are also very prone to being eaten by predators because they can be easily spotted in a small pond. For more information on fish to stock in Pennsylvania ponds, see Fish for Pennsylvania Ponds and for more details on stocking rates, sizes and harvesting see Management of Fish Ponds in Pennsylvania.

Another fish that can be legally used for aquatic plant control in some cases is the grass carp or "white amur". These fish, originally from Asia, have been imported to the United States since the 1960s primarily for control of aquatic plants. In 1994, Pennsylvania made it legal to import grass carp if they are the triploid variety. This means they have been bred to have an extra set of chromosomes and are therefore sterile. Triploid grass carp are not able to reproduce and spread out of control.

Grass carp rely almost entirely on aquatic plants for their diet. According to the PA Fish and Boat Commission, they prefer to eat submerged aquatic plants like pondweeds, elodea, coontail, naiad, and milfoil and even small floating plants like duckweed. While they will eat some algae, especially when they are young, they are not usually able to control filamentous algae. They also will not eat emergent plants like cattails or rooted floating plants like watershield or waterlily. Pond owners who wish to stock triploid grass carp in ponds of 5 acres or less must complete and submit a Triploid Grass Carp Pond Owner Stocking Permit Application and pay a permit fee of $85 to the PA Fish and Boat Commission. Stocking grass carp in ponds and lakes greater than 5 acres requires additional reports, details of which can be found on the permit application. Grass carp can only be purchased from approved triploid grass carp dealers, which are listed on the Pa Fish and Boat Commission website.