Effective stocking densities of triploid grass carp to control aquatic macrophytes

Abstract

Effective use of triploid grass carp Ctenopharyngodon idella for control of aquatic macrophytes requires determination of proper stocking densities. The purpose of this research was to evaluate three stocking densities of triploid grass carp for control of aquatic macrophytes in ponds of the Texas panhandle. Triploid grass carp were stocked in ponds with macrophyte coverage ranging from 0-100%. For each pond, percent macrophyte coverage was estimated monthly along permanent transects with a recording fathometer. Macrophyte community composition, water transparency, and water temperature were also monitored monthly throughout this research. From March 1991 to September 1992, macrophyte coverage decreased 2.7% in ponds stocked with 25 fish ha-1 (vegetated), 21.4% in ponds stocked with 50 fish ha-l (vegetated) and 100% in ponds stocked with 75 fish ha-1 (vegetated). Aquatic macrophytes were eliminated in 12 months from ponds stocked with 75 fish ha-1 (vegetated). Triploid grass carp stocked at 25 fish ha-1 did not allow regrowth of vegetation in ponds that were previously treated with herbicides. Water transparency remained the same in ponds stocked with 25 fish ha-l (vegetated), decreased 1.0% in ponds stocked with 50 fish ha-l (vegetated) , and decreased 58.1% in ponds stocked with 75 fish ha-1 (vegetated).