The Potential of the Hybrid Grass Carp as a Weed Control Agent

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Abstract
Hybrid grass carp, spawned at the Malone Fish Hatchery in 1979, were stocked into two Central Florida lakes containing hydrilla (Blue Lake) and coontail (Crealde Lake) at the rate of 183 fish ha−1 after nearly two years vegetation control was not achieved. A 24% reduction in the number of hybrid grass carp occurred in Blue Lake while an 89% reduction occurred in Crealde Lake. Hybrid grass carp in the coontail lake had a growth rate of 1.3 gm mo−1 while the growth rate in the hydrilla lake was 28 gm mo−1. A total of 49% of the fish in the hydrilla lake was less than 450 gn after 20 mo. Feeding trials in 0.14 ha experimental ponds using triploid hybrid grass carp from Blue Lake revealed that 0.8 kg hybrid grass carp had a feeding rate of approximately one-third less than that of similar sized grass carp and had a growth rate of approximately seven times less. The feeding efficiency of two year old hybrid grass carp was nearly 50% less than for one and one-half year old grass carp. Due to the slower growth, lower feeding rate, and high mortality of hybrid grass carp, the ability of the hybrid grass carp to be used as a low cost, effective weed control agent is doubtful since a longer grow out period to achieve a suitable stocking size and a much larger number of fish will be required.