Establishment of bioenergy models to predict growth, feed requirement and waste output of grass carp (Ctenopharyngodon idella)

In order to predict the growth performance, feed requirement and waste output, and improve the precision of feeding management, the current study reported some bioenergy models developed in grass carp (Ctenopharyngodon idella). In this study, the growth rate of C. idella at different growth stages was calculated by specific growth rate (SGR), daily growth coefficient (DGC), thermal-unit growth coefficient (TGC), average daily growth (ADG) growth models. The optimal growth model was selected by the least squares method. Feed requirement was estimated based on digestible energy requirement (DEreq), calculated from the summation of recovered energy (RE), basal metabolism energy (HeE), heat increment of feeding (HiE), and urinary and branchial energy (UE+ZE), all estimated by compiling and analysing data from published studies. The waste outputs were estimated using a nutrient mass balance approach. Feed requirement model simulations were compared with the results from a growth trial based on C. idella fed with 33%, 28% and 23% crude protein for different growth stages. The result shows that the modified TGC models produced a better fit of the growth trajectory of the fish across production stages compared with other growth models (SGR, ADG, DGC). Values predicted for body weight and feed conversion (FCR, feed: gain) by the models were highly correlated to the observations from the growth trial. The digestible energy requirement is about 1.55×10⁷ kJ for 1 t C. idella with the body weight of 0.5–2 500 g, and total solid wastes (TSW) output of C. idella was estimated at about 440 and 623 kg per tonne of feed fed and per tonne of fish produced, respectively. These results indicate that the model can effectively estimate the growth, feed requirement and waste output in the actual culture operations of C. idella, and could be a valuable tool for the differential marketing, reducing the cost of feed and feed waste, and for pollution assessment.