Evaluation of the net energy value of glucose (cerelose) and maize starch in diets for rainbow trout (Salmo gairdneri)

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Abstract
1. Quadruplicate groups of rainbow trout (Sulmo gairdneri) (mean body-weight 24.9 g) were reared on six dietary treatments (practical-type diets) in a modified paired-feeding experiment for 12 weeks at 15° to determine the net energy (NE) value of starch and glucose to rainbow trout.2. Three test diets were prepared to contain (g/kg): 0 supplemented carbohydrate (diet 1), 250 maize starch (diet 2) and 250 glucose (diet 3) and were givenad lib.to the trout with the feeding rate of the glucose- and starchfed groups being monitored after each feeding. The remaining three treatments involved controlled feeding of the trout with diet 1 at 75% of the feed intake of trout reared on diets 2 and 3, so as to provide the same levels of protein and lipids without carbohydrate, and with diet 2 at 100% of the feed intake of trout reared on diet 3.3. The difference in the final carcass energy of thead lib.-fed group and the respective controlled-fed group divided by the amount of dietary glucose or starch energy consumed by the trout is the NE value for that carbohydrate.4. The determined NE value of glucose was 3.99 kJ/g and starch 2.17 kJ/g, which is 24.6 and 12.6% respectively of the gross energy values of these carbohydrates in rainbow trout.5. The results indicate that digestible energy and calculated metabolizable energy values for carbohydrates in rainbow trout overestimate the utilizable energy content of the diet.6. The determined NE values for glucose and starch in the present study should be used with caution since various factors (such as the feeding rate determined in the present study) may affect the utilization of dietary carbohydrates in rainbow trout.