Effects of dietary protein levels on the growth, body composition, serum biochemistry and digestive enzyme activity in Chinese rice field eel ( Monopterus albus ) fingerlings

Abstract

A 12-week feeding trial was conducted to determine the influence of dietary protein levels on growth performance, body composition, haematological parameters and digestive enzyme activity of Chinese rice field eel (Monopterus albus) fingerlings. Six isolipidic experimental diets (27.89%, 32.23%, 35.95%, 40.06%, 43.31% and 46.53%) were formulated to randomly assign to triplicate groups of 50 rice field eel fingerlings (5.0 ± 0.5 g) cultured in plastic cages. Results indicated that the best growth performance of fish with the highest WG (158.68 ± 31.59%) and SGR (2.28 ± 0.21%) was obtained at 40.06% group. Significant alterations were demonstrated on whole-body crude protein, crude lipid and amino acid profile by different dietary protein levels.Besides, haematological parameters including triacylglycerol, aspartate aminotransferase and alkaline phosphatase decreased with various levels by the increasing of dietary protein levels. The lowest pepsin activity was observed in 27.89% protein group, which suggested lower availability of protein as substrate for protease activity. Meanwhile, the highest amylase activity in fish of 27.89% group indicated higher carbohydrate level in this group. Based on the polynomial regression analysis of WG and SGR, the dietary protein requirement for fingerlings of Monopterus albus was estimated to be 386.4-390.8 g/kg, respectively, with the lipid level of 10.08%. K E Y W O R D S body composition, dietary protein requirement, digestive enzyme activity, growth performance, Monopterus albus, serum biochemistry | 401 YUE Et al.

Effects of Different Dietary Protein Levels on the Growth Performance, Physicochemical Indexes, Quality, and Molecular Expression of Yellow River Carp (Cyprinus carpio haematopterus)

“…These results are consistent with findings on Cyprinus carpio [ 44 , 45 ] and Aristichthys nobilis [ 46 ], implying that the antioxidant capacity of Cyprinus carpio haematopterus will not be weakened by a reduction in dietary protein. The present study also illustrated that the α-AMS, LPS, and TPS activities of the Cyprinus carpio haematopterus intestine first increased and then decreased, results which were observed in previous studies [ 47 , 48 ]. These results demonstrated an increase in the digestive enzyme activities of the fish intestine with the appropriate dietary protein, and excessive protein intake damaged the fish digestive function [ 49 ].…”

Effect of Adding L-carnitine to High-Fat/Low-Protein Diets of Common Carp (Cyprinus carpio) and the Mechanism of Regulation of Fat and Protein Metabolism

“…The increase in TCHO content in plasma will improve blood viscosity, resulting in hyperlipidemia, which is not conducive to the healthy growth of fish. The plasma TCHO of carp was substantially enhanced after feeding with a highfat/low-protein diet in this experiment, putting the common carp's health at risk; similar results have been found with large yellow croaker [6], blunt snout bream (Megalobrama amblycephala) [19], and rice field eel (Monopterus albus) [20]. Ammonia is the end product of amino acid catabolism, accounting for 80-90% of the body's total nitrogen excretion [21].…”

“…Diet 2 had much less protein deposition than Diet 1, implying that a reduction in protein intake from the diet would lead to a decrease in protein deposition in carp muscle. In gibel carp (Carassius gibelio), similar results were observed [24] and rice field eel [20].…”

Effects of Dietary Protein Level on the Gut Microbiome and Nutrient Metabolism in Tilapia (Oreochromis niloticus)

“…Different dietary protein levels can affect the growth, gut microbial composition, nutrient metabolism, and various physiological reactions in fish. In cases of low dietary protein, the activity of various digestive enzymes is decreased, and growth is retarded, ultimately affecting lifespans [ 2 , 3 ]. In cases of high dietary protein level, growth is also retarded; however, instead, the digestion and absorption of nutrients is suboptimal [ 4 ].…”