Hydrilla Consumption by Triploid Hybrid Grass Carp in Aquaria

Triploid hybrid grass carp (Ctenopharyngodon idella x Hypophthalmichthys nobilis) were provided known weights of hydrilla (Hydrilla verticillata) in 300 liter aquaria, to determine consumption rates for age I hybrids from 6 size groups, 21 to 37 cm total length (TL). Mean consumption rates for these groups at 26° C ranged from 25% to 52% of their body weight/day (% BW/D) or 1.7 to 8.6 g dry weight of hydrilla/day (g DW/ D). Smaller hybrids generally ate less hydrilla than larger fish, but expressed as a percentage of their body weight, small hybrids consumed more than large hybrids. The exception was the intermediate size hybrids (31 cm TL group), which consumed significantly (P < 0.05, Tukey's range test) more both in dry weight of hydrilla and in percent body weight than other groups. Regression of dry weight consumed/ day on total hybrid length produced the following equation: g DW/D =-6.1 + 0.039(TL); with a correlation coefficient of 0.82. Since hybrids grew very little (0.1 g/ day) during the 40 to 59 day trials, consumption rates were considered to be near maintenance levels.

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