Abstract
This study was conducted to clarify the energy requirements for maintenance of body weight and activity, and for maximum growth in carp and rainbow trout, specifically examining the effect of feed preparation methods on dietary energy budgets and nitrogen balance. Carp (31g, 17°C), rainbow trout juvenile (31g, 9 and 16°C), and rainbow trout fingerlings (5.7g, 16°C) were fed isocontent ordinary dry pellets (DP) produced by a pellet mill and extruded pellets (EP) by a twin-screw extruder.
Carp fed EP to satiation showed markedly reduced feeding rate, low percent gain and feed efficiency compared to those fed DP to satiation. In rainbow trout EP tended to be generally lower in the feeding rate and higher in the percent gain and feed efficiency than DP at the satiating levels. This tendency was conspicuous for the growth of fingerling and the feed efficiency at a low temperature. The energy digestibility of EP increased from that of DP in rainbow trout, in relation to the gelatinization of starch.
The energy budget in fish fed enough amounts of energy required for maximum growth was determined. The fecal energy loss in DP was relatively large among all the tests, and the digestible and metabolizable energy values of EP were elevated in relation to the fecal energy values. The non-fecal energy losses in rainbow trout were somewhat higher in EP than those in DP. The heat increment of feeding was high in DP and the proportions of productive energy were high in EP in all the experiments.
