Syx62

All experimental conditions and protocols were approved by the Animal Ethic Advisory Committee of Sichuan Agricultural University under permit No. DKY-S20170512. The proximate composition of the basal diet is given in the additional files (Table S1), which is the same as our previous study [10 (link)]. Fish meal, soybean meal, rapeseed meal, and corn gluten meal were used as the primary protein sources. Soybean oil and wheat flour were used as the main lipid and starch sources. Dietary crude protein and lipid were fixed at 387.8 and 71.0 g/kg diets respectively. The Ile concentrations of seven experimental diets were 5.0 (control diet), 7.5, 10.0, 12.5, 15.0, 17.5, and 20.0 g/kg diet. All diets were made iso-nitrogenous with the addition of appropriate amounts of glycine. After thoroughly mixing all diet ingredients, water was added to achieve a proper pelleting consistency and pelleted mixture through the screw Extruder (SYX62, Xiamen, China) at 2-mm diameter. The processing conditions were as follows: 100 r/min screw speed, 127 °C temperature, and 30–45 atm pressure. Floating extruded pellets were air-dried and then stored at − 20 °C in plastic bags until used.

Formulation and proximate chemical composition of the trial diets are shown in Table 1 (Huang et al., 2021 (link)). Two (49% crude protein) and isolipidic (9% crude lipid) semi-purified diets were formulated with α- cassava starch (0 and 220 g/kg), named as Z diet and G diet, respectively. Briefly, all dry ingredients were crushed and sifted through 280 μm mesh, then weighed according to the ratio and mixed manually for 10 min. The mixed ingredients were transferred to a pelletizer (SYX62, Xiamen, China) and processed into 2 mm diameter pellets. All diets were air-dried at room temperature (23°C–30°C) and stored at −20°C until use.
The chemical composition analyses of the diets were conducted by standard methods (AOAC, 2005 ). Crude protein, crude lipid, and ash were determined by Kjeldahl method (N × 6.25) (Kjeltec 2300, FOSS, Hilleroed, Denmark), petroleum ether extraction (without acid hydrolysis) using Soxtec (Soxtec 2055; FOSS), and combustion at 550°C to constant weight in a muffle furnace (Shenyang Energy-saving Electric Furnace Factory, Shenyang, China). Optical rotation method was used to determine the starch content (spectropolarimeter WZZ-2B, Shanghai, China).