Hydrilla Consumption by Triploid Grass Carp

Triploid grass carp (Ctenopharyngodon idella, 2n = 72) were found to consume an average of 127 ± 17% of their body weight in fresh hydrilla (Hydrilla verticillata) per day. Experimental fish were 199 ± 27 g at the outset, and during the 51-day trial, the 6 fish gained an average of 3.3 ± 0.5 g/ day. Total lengths increased from 243 ± 10 mm to 301 ± 15 mm (1.1 ± 0.2 mm/day) during this time. These values are equivalent to results reported by other researchers for diploid grass carp and are 3 to 4 times greater than for triploid hybrid grass carp (C. idella X Hypophthalmichthys nobilis, 2n = 72) tested in 1983. Food conversion efficiency was 60 ± 8%. Triploid grass carp were also effective in removing hydrilla from 2 0.1-ha hatchery ponds. Fish (x = 196 g) were stocked at a rate of 250/ha in 1 pond and 500/ha in the other. At the conclusion of the study 9 months later, hydrilla was absent from the pond, except for within control exclosures. Upon harvesting, 90% of the fish from 1 pond and 96% from the other were recovered. During the test they had grown to a mean weight of 2.1 kg.

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10180