Grass carp, or white amur (Ctenopharyngodon idella) are originally from China. They are a different species from the common carp. Aptly named, grass carp feed on vegetation, and will consume pelleted food when available. They can grow to 35 kg, however they rarely exceed 10 kg when stocked in ponds.
Kenneth Williams and Glen Gebhart have published a report entitled Controlling Aquatic Vegetation with Grass Carp. From the introduction:
Excess aquatic vegetation causes problems in both aquaculture ponds and in farm ponds used for either sport or food fish production. The main problems caused by rooted and filamentous aquatic vegetation in aquaculture ponds are: interference with fish harvest operations, use of nutrients that could be more efficiently utilized by phytoplankton for dissolved oxygen production, reduction of water circulation that increases stratification and lowers dissolved oxygen levels. Excess aquatic vegetation in farm ponds interferes with hook and line harvest and increases the possibility of overpopulated, stunted forage fish populations, and reduces the aesthetic value of the pond for swimming and recreation. Grass carp are used to great advantage in both situations.
Grass carp do not breed easily in ponds, in their natural environment preferring swift moving water. Kenneth Williams, again, has published information on Grass Carp Propagation. From the introduction:
Spawning does not occur in ponds and lakes. Reproductive organs reach an incomplete state of development and become dormant. As water temperature rises above 80 degrees F. eggs and milt are resorbed into the fish.
Natural spawning conditions do not exist for grass carp in the United States with the possible exception of the Mississippi river. Successful grass carp spawning and hatching requires a thorough knowledge of the fish, healthy brood stock, gentle handling and an understanding of induced hormonal spawning techniques.
Michael P. Masser has published a document July 2002, entitled Using Grass Carp in Aquaculture and Private Impoundments. From the abstract:
The U.S. Fish and Wildlife Service, in cooperation with Auburn University, first introduced grass carp into the U.S. in 1963 to investigate their usefulness in controlling aquatic vegetation. No native North American species of fish is as strictly herbivorous as the grass carp. Therefore, there are no native species available for aquatic vegetation management. Grass carp have proven to be effective in controlling many species of algae and submerged aquatic vegetation.
Larry Sanders, Jan Jeffrey Hoover, and K. Jack Killgore have published a 1991 report entitled Triploid Grass Carp as a Biological Control of Aquatic Vegetation. Triploid grass carp are sterile, thus eliminating the concern of the species forming sustainable, breeding populations. The article reviews
the development and biology of the triploid grass carp and provides recommendations for its use as a biological control of nuisance aquatic vegetation. Triploid and diploid grass carp are morphologically identical and, reproduction notwithstanding, are assumed ecologically similar. Therefore, most data obtained from studies of diploid fish should be applicable to triploid fish.
Aquaculture CRSP report on the Polyculture of Grass Carp and Nile Tilapia with Napier Grass as the Sole Nutrient Input in the Subtropical Climate of Nepal. The objectives of the research:
1) Evaluate the growth of grass carp and tilapia fed with napier grass in polyculture.
2) Evaluate the nutrient and water quality regimes of pond water.
3) Determine the composition of foods consumed by Nile tilapia.
4) Determine the optimal ratio of grass carp to Nile tilapia in polyculture.
The FAO have published a summary of grass carp culture entitled Cultured Aquatic Species Information Programme Ctenopharyngodon idella. As part of a section on status and trends, they observe:
Grass carp not only grow quickly but have a low requirement for dietary protein. They can be produced at low cost by feeding them with aquatic weeds, terrestrial grasses and by-products from grain processing and vegetable oil extraction. Seed can be produced through induced breeding at a large scale and very low cost. The culture of grass carp can be well integrated into crop farming and animal husbandry, to maximize the utilization of natural resources. On the other hand, it is a large fish without fine inter-muscular bones. It is acceptable to consumers in many countries and it very likely has good potential for development. The market for grass carp is close to saturation in the eastern part of China, where aquaculture is well developed now. However, there is still a considerable potential market in central and western China and many other developing countries.