Energy Balances of Diploid, Triploid, and Hybrid Grass Carp

Abstract

Grass carp Ctenopharyngodon idella and genetic derivatives are widely used as biological control agents for aquatic macrophytes. The results of bioenergetic comparisons of three types of commercially available grass carp are reported. Empirical relationships were developed for consumption rate, metabolic rate, and assimilation efficiency as functions of temperature and size. Summary energy balances are presented for each type of fish. Diploid and triploid grass carp had similar standardized energy balances: 12–13% of the energy ingested was used in metabolism, 74% was egested or excreted, and 13–14% went into growth. Hybrid grass carp (female grass carp x male bighead carp Hypophthalmichthys nobilis) metabolized a greater proportion of the energy intake (16%) and egested 81%, leaving only 3% available for growth; they also ingested food at a significantly lower rate. Thus, intergeneric triploid hybrids appear to be energetically handicapped. Their low consumption rate and reduced assimilation efficiency, coupled with elevated metabolic costs, leave little energy available for somatic growth. High rates of growth of diploid and triploid grass carp are attributed to their “low efficiency‐high volume” energetic strategy, which is quite successful as long as food supplies allow them to feed ad libitum.

Growth and Population Size of Grass Carp Incrementally Stocked for Hydrilla Control

“…Proportion of the Grass Carp population size accounted for by individuals older than age 10 (upper panel) and the proportion of Grass Carp population biomass contributed by individuals older than age 10 (lower panel) in Lake Gaston. Population size and biomass were estimated by using mortality derived from the methods of Pauly (1980;M p ) and Jensen (1996; ) across all ages or by using age-specific mortality derived from the method of Chen and Watanabe (1989;M cw ). to mass, whereas the standard metabolic rate and energy per gram of wet weight are positively related to mass (Wiley and Wike 1986). These factors cause an increase in the energy required per unit of mass gained by Grass Carp as they grow larger; greater energetic requirements necessitate increased hydrilla consumption by the fish in Lake Gaston.…”

“…Based on the bioenergetics of Grass Carp (Wiley and Wike 1986) and the linear patterns of weight gain observed in Lake Gaston and other systems (e.g., , it is likely that Grass Carp older than age 10 also make important contributions to weed control. In Lake Gaston, fish exceeding age 10 made substantial contributions to the total biomass-but not the number-of Grass Carp in the system.…”

The biology of triploid fish

“…The feed conversion efficiency has been well studied in triploid grass carp (Wiley and Wike, 1986), African catfish (Clarias gariepinus) (Henken et al, 1987) and rainbow trout (Oliva-Teles and Kaushik, 1990b). No significant differences were observed in protein efficiency ratio, net protein utililization, efficiency of energy gain, total energy intake and nitrogen balance in these species.…”

Triploid Grass Carp Susceptibility and Potential for Disease Transfer when used to Control Aquatic Vegetation in Reservoirs with Avian Vacuolar Myelinopathy

“…Seasonality (i.e., cool water temperatures) may have prevented the Grass Carp in the field trial from consuming enough material to reach the threshold necessary for eliciting clinical signs or mortality. Grass Carp consume the most vegetation when water temperatures range from 20 • C to 30 • C, stop feeding at temperatures below 11 • C, and feed intermittently at temperatures between 11 • C and 20 • C (Heidinger 1983;Young et al 1983;Wiley and Wilke 1986). Similarly, decreased appetite due to captivity likely prevented the laboratory Grass Carp from consuming a dose that would be sufficient to produce clinical signs or mortality.…”