Effect of temperature on the digestibility of non-starch polysaccharide-rich ingredients in Nile tilapia (Oreochromis niloticus)

This study aimed to investigate the interaction effect of NSP-rich ingredient and rearing temperature on nutrient digestibility of the ingredients in Nile tilapia. Seven NSP-rich ingredients were tested: insect meal, wheat bran, palm kernel meal, rapeseed meal, sunflower meal, dried distillers grains with solubles (DDGS) from corn, and rice bran. A balanced control diet was formulated followed by the formulation of seven test diets by mixing 30 % of each test ingredient with 70 % of the control diet and fed to fish reared at 24 or 32 °C. At each temperature, 35 all male Nile tilapia with an initial mean weight of 45.0 g at 24 °C and 43.8 g at 32 °C were housed in each of 24 glass-tanks, each containing 60 L of water. The diets were administered to the fish groups in triplicate over 42 d in a recirculating aquaculture system. Fecal samples were collected and analyzed alongside the diets to determine nutrient digestibility. Digestibility of all nutrients differed between ingredients (P < 0.001) at both temperatures. Wheat bran had the lowest NSP digestibility at both 24 (1.9 %) and 32 °C (9.7 %). At 24 °C, DDGS showed the highest NSP and protein digestibility (41.4 and 90.3 %), while at 32 °C insect meal showed the highest NSP and fat digestibility (59.8 and 97.5 %). Insect meal showed the highest fat digestibility (97.4 %) also at 24 °C. An interaction effect between ingredient and temperature was observed for the digestibility of NSP, carbohydrate, protein, amino acids, magnesium, and dry matter (P ≤ 0.035). Some nutrients showed reduced digestibility for some ingredients at the higher temperature, but in most of the cases temperature increased nutrient digestibility, with insect meal exhibiting a 20 % increase in NSP digestibility. In conclusion, water temperature affect nutrient digestibility, but the extend of the temperature effect differs between ingredients.