Energy utilisation efficiencies of digested protein, fat and carbohydrates in striped catfish (Pangasius hypophthalmus) for whole body and fillet growth

This study aimed to assess the effect of dietary macronutrient composition on the relationship between RE and DE intake (i.e., the maintenance energy requirements and the slope [kg_DE]); to quantify the energy utilisation efficiencies of digested protein, fat and carbohydrates for whole body growth as well as fillet growth in striped catfish (Pangasius hypoththalmus). To achieve these aims, a 63-day experiment was conducted on striped catfish (29.1 g). A total of 4 diets were studied at 2 feeding levels, low vs. high (12 vs. 22 g.kg^−0.8.d⁻¹, respectively), which resulted in a 4 × 2 factorial design. The four diets had contrasting inclusion levels of protein, fat and carbohydrates. Striped catfish digested part of the non-starch polysaccharides (33.6–71.0%) while starch is almost completely digested (> 94%). By conducting the regression between RE and DE intake over diets, the energy utilisation efficiency for striped catfish was estimated at 71% through the equation: RE = − 42 (se 9.2) + 0.71 (se 0.049) DE intake, (R² = 0.95). Dietary macronutrient composition did not affect the relationship between RE and DE intake. Multiple regression between RE as a function of digested protein, fat and carbohydrates intake (in g.kg^−0.8.d⁻¹) was also conducted to estimate the energy utilisation efficiency of digested protein, fat and carbohydrates. The estimated energy efficiencies of digested protein, fat and carbohydrates for energy retention at the whole fish level were 64%, 80% and 58%, respectively. The energetic values of dCP, dFat and dCarb for whole body growth differ from the energetic values for fillet production. For fillet growth, digested protein had a higher potential compared to digested fat and carbohydrates, however this needs to be used in a balanced ratio with digested fat and carbohydrates.