Oxidation of phenylalanine and threonine in response to dietary arginine supply in rainbow trout (Salmo gairdneri R.)

Physiological and transcriptomic responses to fishmeal-based diet and rapeseed meal-based diet in two strains of gibel carp (Carassius gibelio)

The present study investigated differences in the utilization of fishmeal (FM) and rapeseed meal (RM) by gibel carp (Carassius gibelio) and explored the effects of protein sources on the responses of different genotypes. Gibel carp strains A (4.12 ± 0.03 g) and F (3.47 ± 0.00 g) were fed FM diet or RM diet for 56 days, and after which, growth performance, body composition, hematologic indices, and hepatic transcriptomes were measured. The effects of strain and diet on growth performance, body composition, and hematologic indices were analyzed by two-way analysis of covariance (ANCOVA). The results revealed that total replacement of FM with RM caused poor growth and feed utilization in both strains as well as the existence of genotype-diet interactions. Strain A showed better growth performance than strain F in the FM group, while the strain F grew better than strain A in the RM group. Transcriptomic analysis showed that the three main biological processes affected by the RM diet were amino acid metabolism, lipid metabolism, and digestive system. The different responses to the RM diet between strains were involved in amino acid metabolism, immune responses, and lipid metabolism. Identifying the underlying mechanisms by which different strains differently respond to meal sources might be the basis to develop a selective breeding program towards strains accepting alternative meal sources.

Dietary arginine affects growth, gut morphology, oxidation resistance and immunity of hybrid grouper (Epinephelus fuscoguttatus♀×Epinephelus lanceolatus♂) juveniles

An 8-week growth trial was conducted to evaluate the effects of dietary arginine (Arg) levels on growth, gut morphology, oxidation resistance and immunity of hybrid grouper (Epinephelus fuscoguttatus♀×Epinephelus lanceolatus♂) juveniles. Seven isoenergetic (1465 kJ (350 kcal)/100-g DM), isoproteic (53·5 % of DM) and isolipidic (7 % of DM) experimental diets were formulated to contain graded Arg levels ranging from 1·9 to 4·7 % (dry weight) at approximately 0·5 % increments. Each diet was randomly assigned to triplicate groups of 16 juvenile fish (average initial body weight: 11·7 (sd 0·1) g) and was administered twice daily (08.00 and 16.00 hours). After the growth trial, all remaining fish were fed their prescribed diets for 2 d and then exposed to 4·5 mg Cu2+/l water for 36 h. Results showed that growth performance and feed utilisation of experimental fish were significantly affected by different dietary Arg levels. Weight gain % (WG%) of fish was increased as dietary Arg increased, reaching a peak value at 3·8 % dietary Arg level, and when dietary Arg level increased to 4·7 % WG% was reduced. Fish fed 1·9 and 2·2 % dietary Arg levels had higher daily feed intake compared with fish fed other dietary Arg levels. Feed conversion ratios in fish fed 1·9, 2·2, 2·7 and 4·7 % dietary Arg levels were higher than those in fish fed 3·1, 3·8 and 4·1 % dietary Arg levels. Protein efficiency ratio and protein productive value (PPV) increased with an increase in dietary Arg, up to a peak value at 3·8 % dietary Arg level, above which these parameters declined. On the basis of quadratic regression analysis of weight gain % (WG%) or PPV against dietary Arg levels, the optimal dietary Arg requirement for hybrid grouper was estimated to be 3·65 %. Fish fed 3·8 % dietary Arg had higher whole-body and muscle protein contents compared with fish fed other dietary Arg levels. Fish fed 3·8 and 4·1 % dietary Arg levels had higher levels of mRNA for insulin-like growth factor-I and target of rapamycin in the liver compared with fish fed other dietary Arg levels. Hepatic S6 kinase 1 mRNA expression in fish fed 3·8 % dietary Arg level was higher than that in fish fed any of the other dietary Arg levels. Gut morphology, hepatic antioxidant indices and immune indices in serum and head kidney were significantly influenced by dietary Arg levels. In conclusion, the optimal dietary Arg requirement for hybrid grouper was estimated to be 3·65 %, and suitable dietary Arg supplementations improved gut morphology and oxidation resistance of hybrid grouper.

Effects of arginine on pancreatic hormones and hepatic metabolism in rainbow trout

Arginine (Arg), injected intraperitoneally into rainbow trout (Oncorhynchus mykiss), increases plasma concentrations of glucagon, glucagon-like peptide-1 (GLP-1), and insulin by three- to 10-fold. Resulting ratios of glucagon and GLP-1 over insulin are unchanged in 20-d food-deprived fish (saline, 1.28 vs. Arg, 0.93; not significant) while slightly increased in feeding trout (saline, 0.70 vs. Arg, 0.92; P<0.05). In food-deprived juveniles, Arg injection leads to significant decreases in plasma fatty acids (saline, 1.65 mM L(-1) vs. Arg, 1.09 mM L(-1); P<0.05) and increases in glycogen phosphorylase total activity (saline, 3.7 units g(-1) vs. Arg, 4.6 units g(-1); P<0.05) and degree of phosphorylation (saline, 1.7 units g(-1) vs. Arg, 2.33 units g(-1); P<0.05). Plasma and liver glucose and liver enzymes (glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, pyruvate kinase, phosphoenolpyruvate carboxykinase, lactate dehydrogenase, and malic enzyme) are unaffected. Otherwise, fish show the changes in plasma metabolites expected with food deprivation. Arg injection into feeding fish results in decreases in plasma fatty acids, liver glycogen, and glucose, while liver glucose 6-phosphate concentrations increase. Hepatocytes isolated from feeding fish injected with Arg 2 h previously show significantly lower rates of lactate oxidation than controls (85% of control), while rates of gluconeogenesis and hormonal responses to mammalian glucagon and GLP-1 remain unchanged. Rates of lactate oxidation and gluconeogenesis are significantly decreased by 5%-10% on treatment with porcine insulin. Complete immunoneutralization of insulin with rabbit antisalmon insulin serum decreases hepatic glucose 6-phosphate concentrations and abolishes the Arg-dependent effects on glycogen phosphorylase. It appears that short-term increases in pancreatic hormones cause only minor metabolic readjustments in the relatively short time frame covered in these experiments. Surprisingly, complete removal of insulin does not have immediate altering or detrimental effects on key metabolites and metabolic pathways, even if glucagon and GLP-1 concentrations are concurrently several-fold higher than usual. Our data clearly show the dual role of Arg in fish metabolism.