Apparent digestibility of protein, energy and amino acids in nine protein sources at two content levels for mandarin fish, Siniperca chuatsi

In order to maximize the output, minimize the waste produced by the fish, and develop nutritionally adequate diets, the digestibility and nutritional value of feed ingredients were evaluated. The objective of this study was to determine apparent digestibility coefficients (ADCs) of dry matter, crude protein, gross energy, phosphorus, and amino acids in feed ingredients for mandarin fish, Siniperca chuatsi with initial average body weight of 31.27 ± 1.64 g. Nine experimental ingredients including white fish meal (WFM), meat and bone meal (MBM), maggot meal (MGM), soybean meal (SBM), fermented soybean meal (FSBM), peanut meal (PNM), corn gluten meal (CGM), cottonseed meal (CSM), and rapeseed meal (RSM) were added to reference diet containing 53% (WFM) at two levels of 15 and 30%. The ADCs of dry matter at the level of 30% were higher than those at the level of 15% in mandarin fish fed with the diet with WFM. In addition, the highest ADCs of dry matter (80.96%) was observed in fish fed with the diet with WFM at the content level of 30%, followed by lower ADC of the ingredients with FSBM, MGM, CGM, SBM, MBM, PNM, CSM, and RSM. However, the ADCs of dry matter in mandarin fish fed with the diet at the level of 15% were higher than those at the level of 30% in MBM, CGM and PNM. The results indicated that ADCs of the experimental ingredients were significantly affected by the ingredient type and the content level. The highest digestion of protein (88.90%) was also observed in WFM at the level of 30%, followed by FSBM (83.93%) and MGM (82.59%) at 30% content level, MGM and FSBM at 15% content level and CGM at 30% content level. Lipid ADCs of WFM, MBM, SBM, FSBM, CGM and CSM ranged from 83.96 to 93.25%, indicating that the lipid of these ingredients was efficiently digested by mandarin fish. The highest digestibility coefficient of energy (88.74%) was registered in WFM at 30% content level, followed by MGM at 30% content level, and the lowest digestibility coefficient of energy (49.24%) was recorded in RSM at 30% content level (P < 0.05). In addition, the apparent digestibility of phosphorus in animal feeds and plant feeds ranged from 35.75 to 63.91% and from 42.21 to 66.77%, respectively. Amino acids digestibility followed a similar pattern to those of ADCs of protein in the animal feeds. Amino acids digestibility in WFM and MGM were generally higher than those in MBM among all the plant feeds. The digestibility of amino acids in FSBM, SBM, and CGM were higher than those in RSM and CSM. In conclusion, these data provide more precise information concerning nutrient and energy utilization of Siniperca chuatsi and will allow ingredient substitutions in practical feed based on levels of available nutrients. Based on the current findings, we propose that FSBM, MGM, SBM, and CGM could be considered for incorporation into formulated diets for mandarin fish.