Effect of temperature on the energy utilization efficiencies of digested protein, fat, and carbohydrates in Nile tilapia (Oreochromis niloticus)

Summary

Most effective feed formulations for fish have historically relied mainly on digestible energy (DE) but recently also on net energy (NE) approaches, which indicate how energy or macronutrients are utilized for growth or energy retention (RE). This study aimed to determine the effect of temperature on 1) DE-based feed formulations that explored the relationship between DE intake and RE, and 2) NE-based feed formulations that examined the energy utilization efficiency of macronutrients, specifically digested protein (dCP), fat (dFat), and carbohydrate (dCarb) for growth in Nile tilapia. The study involved two separate experiments, one at 24 °C and one at 32 °C for Nile tilapia (initial weight ∼ 38 g). Four diets having contrasting levels of protein, fat, and carbohydrates were used; and two feeding levels (FL; 10 vs. 18 g.kg−0.8.d−1) were applied. Digestibility of protein differed more between FLs at 32 °C. In contrast, fat and carbohydrate digestibility differed more between FLs at 24 °C. The slope of the relationship of RE to DE intake differed between 24 and 32 °C at one of the four diets (P < 0.05), which implies that the DE value of diets/ingredient is dependent on temperature. RE was related to dCP, dFat, and dCarb intake at 24 °C as RE = −27.6 (SE 2.86) + 13.3 (SE 0.53) dCP + 32.0 (SE 0.81) dFat +10.9 (SE 0.43) dCarb, R2 = 0.99 and at 32 °C as RE = −54.4 (SE 5.43) + 14.7 (SE 0.96) dCP + 32.7 (SE 1.46) dFat +10.6 (SE 0.77) dCarb, R2 = 0.98. Fasting heat production increased with temperature (27.6 vs. 54.4 kJ.kg−0.8.d−1; P < 0.05). The energy utilization efficiencies of dCP, dFat, and dCarb were similar at 24 and 32 °C (P > 0.05); being 56, 81, and 63% at 24 °C and 62, 83, and 62% at 32 °C. The practical implication of this is that the NE approach of feed evaluation for Nile tilapia is independent of water temperature.