Aquatic Weed Control by Grass Carp in Cool Waterby Joan S. Thullen, US Bureau of Reclamation, United States,
Abstract: Diploid grass carp have significantly controlled problem aquatic vegetation during a 3-year study in a northern Colorado irrigation canal where water temperatures ranged from 0 to 25°C. The aquatic weeds which were controlled included elodea, leafy pondweed, sago pondweed, and horned pondweed. Initial fish stocking densities throughout the study ranged from 63 to 363 kg/ha (32 to 388 fish/ha) and each density was effective in controlling the weeds. Evidence of fish migration downstream made it necessary to augment the lowest stocking density (63 kg/ha) in order to control the regrowth of the weeds. At the end of 3 years, the average grass carp had increased in weight by 343% and in length by 55%. During the first overwintering period, the fish lost only 4% of their biomass while during the second, which lasted substantially longer, the loss was 20%. This weakened their general condition but most of the loss was regained during the next irrigation season.
Subject Headings: Vegetation | Aquatic habitats | Irrigation | Fish management | Canals | Water temperature | Irrigation water | Temperature effects | North America | Colorado | United States
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