Assessment Of Arginine Requirement For Largemouth Bass, Micropterus Salmoides

An 8-week feeding test was conducted to quantify the dietary arginine requirement of juvenile largemouth bass (25±0.4g) reared in indoor flow-through and aerated aquaria. Six isonitrogenous and isoenergetic (46% crude protein and 21.6 kJ/g dry diet) diets were formulated to contain graded levels of arginine (1.70%, 1.97%, 2.24%, 2.51%, 2.78% and 3.01%, of dry diet). Zein-coated crystalline amino acid mixture was supplemented in test diets to simulate, except for arginine, the amino acid profile of largemouth bass muscle protein. Each diet was randomly assigned to quadruplicate groups of 35 juvenile fish. Fish were fed by hand to apparent satiation twice daily (08:00 and 16:00). During the experiment period, water temperature was maintained at 28±1°C; pH, 7.2-7.6; ammonia nitrogen, lower than 0.3 mg/L. The natural light cycle was adapted.The results of this study are as follows:The growth performance of largemouth bass (LMB) was significantly affected by dietary arginine levels. Weight gain (WG, g kg-1 ABW day-1) and specific growth rate (SGR) increased significantly with increased dietary arginine level from 1.70% to 2.24% (P<0.05) and then leveled off. Survival rates of fish fed diets with graded arginine levels were above 98%, and no pathological signs of arginine deficiency were observed among treatmentsNitrogen retention (NR) was significant lower in fish fed diet containing 1.70% arginine (P<0.05). Arginine retention was significantly lower in fish fed diet containing 2.76% and 3.01% arginine, compared with other dietary arginine levels (P<0.05). Meanwhile, retentions of other essential amino acids were significantly increased with increased dietary arginine levels from 1.70% to 2.24% (P<0.05) and then leveled off. Voluntary feed intake in fish fed diet containing 3.01% dietary arginine was significantly higher than in fish fed diet containing 1.70% and 1.97% arginine (P<0.05). Protein efficience ratio was not affected by dietary arginine levels (P>0.05). Apparent digestibility of arginine was significantly increased with dietary arginine increasing (P<0.05).Whole-body crude protein content was significantly affected by dietary arginine levels(P<0.05). Condition factor (K), hepatosomatic index (HSI) and viscerosomatic index (VSI) were not affected by dietary arginine levels (P>0.05). Except for a few amino acids (Thr, Leu, Lys), the essential amino acid composition of the whole body were not affected by dietary arginine levels (P>0.05).There are no significant differences in the haematological paramenters in red blood cell counts, haemoglobin concentration (Hb) and haematocrit (Hct) with fish ingesting different dietary arginine levels (P>0.05). The lysozyme activity of the serum was higher in fish fed diet containing 2.76% arginine(P>0.05).The respiratory burst activity of head kidney leukocytes was significantly higher (P<0.05) in fish fed diets containing 3.01% dietary arginine, compared to those of fish fed the diets containing lower dietary arginine levels; while classical complement pathway (CH50) showed no difference among treatments (P>0.05). The serum protein was significantly higher in fish fed diets containing 1.97% and 2.23% arginine than in the other fish (P<0.05). Based on broken-line analysis for SGR and NR against dietary arginine level, the optimum requirement of largemouth bass for dietary arginine was 1.98% - 2.20% of dry diet (4.31% - 4.79% of dietary protein).