Effects of dietary docosahexaenoic acid on growth performance,fatty acid profile and lipogenesis of blunt snout bream (Megalobrama amblycephala)

Six diets were designed to investigate the effects of dietary docosahexaenoic acid (22:6n‐3; DHA) levels (0.5, 1.3, 2.3, 4.2, 8.1 and 15.9 g/kg diets) on growth performance, fatty acid profile and expression of some lipogenesis‐related genes of blunt snout bream (Megalobrama amblycephala). Fish (average weight: 26.40 ± 0.11 g) were randomly fed one of six diets for 8 weeks. Results indicated that the final body weight (FBW) and specific growth rate (SGR) of fish fed 1.3 g/kg DHA were significantly higher than other groups except for the 2.3 g/kg DHA (p < .05). Compared with other groups, the number of lipid droplet clusters of the liver stained with oil red O in the 2.3 g/kg DHA group was the highest, which was consistent with the lipid contents of whole body and liver. The DHA proportion in liver and muscle significantly increased with the increasing dietary DHA levels (p < .05), which reflected fatty acid profiles of diets. The highest mRNA expressions of acetyl‐CoA carboxylase α (ACCα), fatty acid synthase (FAS) and sterol regulatory element‐binding protein‐1 (SREBP‐1) occurred in the 1.3 g/kg DHA group, followed by 2.3 g/kg DHA. In summary, the supplementation of 1.3–2.3 g/kg DHA could improve growth performance and lipogenesis, and the dietary DHA could improve DHA and PUFA proportion in liver and muscle.     

Molecular adaptations of glucose and lipid metabolism to different levels of dietary carbohydrates in juvenile Japanese flounder Paralichthys olivaceus

Japanese flounder juveniles (initial body weight: 7.12 ± 0.02 g) were fed three diets containing 0, 120 and 200 g/kg of carbohydrates (C0, C120 and C200, respectively) for 10 weeks. Results showed that higher dietary carbohydrate intake enabled further deposition of glycogen and lipids in liver and muscle. The mRNA levels of glucokinase (gck), phosphofructokinase (pfkl) and hexokinase (HK) activity involved in glycolysis were significantly up‐regulated in C120 (p < .05) but showed no further up‐regulation except for gck in C200. Besides, the gluconeogenic phosphoenolpyruvate carboxykinase 1 (pck1) mRNA levels were down‐regulated significantly in fish fed the C120 (p < .05). However, further increase in dietary carbohydrate levels increased the mRNA levels and activities of enzymes involved in gluconeogenesis and lipolysis (p < .05). Additionally, plasma glucose remained unchanged in C120 (p > .05) but significantly increased in C200 group (p < .05). In conclusion, Japanese flounder was able to use carbohydrates efficiently through regulation of glucose and lipid metabolism when dietary carbohydrate was not higher than 120 g/kg, while 200 g/kg of dietary carbohydrate caused the deregulation of glucose homoeostasis.     

Effects of dietary starch levels on the growth,plasma metabolites and expression of genes involved in glucose transport and metabolism in Pelodiscus sinensis juveniles

A 10‐week feeding trial was conducted to evaluate the growth performance, glucose transport and metabolism of Chinese soft‐shelled turtles (Pelodiscus sinensis) exposure to graded levels of dietary starch (0.52%, 7.43%, 14.74%, 22.99% and 31.38%). The 360 turtles (initial body weight, 12.94 ± 0.50 g) with 12 replicates were randomly assigned to five experimental diets. The highest weight gain and specific growth rate (SGR) were observed in 7.43% group and the lowest in 31.38% group. The protein efficiency ratio, whole‐body lipid contents, hepatic glycogen contents and the 4‐hr postprandial plasma glucose levels were significantly increased with the increment of starch levels (p < .05). In contrast, the daily feed intake and feed conversion ration were significantly declined (p < .05). The mRNA levels of glucose transporter 2, glucokinase, pyruvate kinase, malic enzyme and acetyl‐CoA carboxylase alpha genes in the liver significantly increased as the increase in starch levels at 4‐hr and 24‐hr post feeding (p < .05). No significant differences were observed in the expression of gluconeogenesis genes at each time point (p > .05). These results suggested that dietary addition of starch up‐regulated hepatic glycolysis, glycogenesis and lipogenesis genes expression, but the deficient response of gluconeogenesis to dietary starch might be part of the causes limited the starch utilization. Based on the secondary polynomial regression of SGR, y = ?0.0011x² + 0.028x + 1.63 (R² = 0.9292), the 12.73% inclusion level of dietary starch was recommended in juvenile turtles.     

Dietary n‐3 highly unsaturated fatty acids affect the biological and serum biochemical parameters,tissue fatty acid profile,antioxidation status and expression of lipid‐metabolism‐related genes in grass carp,Ctenopharyngodon idellus

A 95‐day feeding trial was conducted to determine the effects of n‐3 highly unsaturated fatty acids (n‐3 HUFA) on the growth, antioxidation and lipid metabolism in grass carp (Ctenopharyngodon idellus). Two isonitrogenous and isolipidic diets were formulated with either lard oil (LO) or fish oil (FO) as the main lipid source. The results showed that the intraperitoneal fat (IPF) ratio was significantly lower (P < 0.05) in FO group. The concentration of n‐3 HUFA in muscle, hepatopancreas and IPF was significantly higher in FO group (P < 0.05). The serum low‐density lipoprotein (LDL) content was significantly lower (P < 0.05), and glucose (GLU) content was significantly higher (P < 0.05) in FO group. The serum total superoxide dismutase (T‐SOD) activity was significantly higher (P < 0.05) in FO group, consistent with the serum malondialdehyde (MDA) content. The gene expression of IPF fatty acid synthase (FAS), acetyl‐CoA carboxylase (ACC), sterol regulatory element‐binding protein (SREBP‐1) and peroxisome proliferator‐activated receptor γ (PPARγ) was significantly lower (P < 0.05) and that of peroxisome proliferator‐activated receptor α (PPARα) was significantly higher (P < 0.05) in FO group compared with LO group. Similar trends were found in the hepatopancreas, except for PPARγ. It is suggested that n‐3 HUFA could inhibit lipid accumulation in grass carp by affecting the expression of lipid‐metabolism‐related genes.     

High dietary starch impaired growth performance,liver histology and hepatic glucose metabolism of juvenile largemouth bass,Micropterus salmoides

A 60‐day experiment was carried out to investigate dietary starch levels on growth performance, hepatic glucose metabolism and liver histology of largemouth bass, Micropterus salmoides. Fish (initial weight 22.00 ± 0.02 g) were fed five graded levels of dietary corn starch (0, 50, 100, 150 and 200 g/kg). Fish fed low (0 and 50 g/kg) dietary starch showed significantly higher weight gain than other groups (p < .05). Liver lipid and glycogen accumulations were induced when dietary starch higher than 100 g/kg. After 20 days of feeding, hexokinase activity and mRNA expression were decreased in fish fed dietary starch higher than 150 g/kg (p < .05) and the pyruvate kinase showed the opposite tendency. Insulin receptor 1 (irs1), glucagon‐like peptide‐1 receptor and glucose transport protein 2 (glut2) mRNA expression were decreased with the increasing dietary starch after 10 days of feeding (p < .05). These results indicated gluconeogenesis was depressed and β‐oxidation was enhanced in response to high dietary starch, while the glycolysis was inhibited and endocrine system was impaired when fish fed high dietary starch; then, glucose homeostasis was disturbed and finally led to the glucose intolerance of largemouth bass.     

Effects of different dietary lipids on growth,body composition and lipid metabolism‐related enzymes and genes in juvenile largemouth bass,Micropterus salmoides

This study investigates the effects of different lipids on growth, body composition and lipid metabolism of largemouth sea bass fish Micropterus salmoides. A total of 360 juvenile M. salmoides (mean ± SD mass = 33.83 ± 0.15 g) were randomly stocked into 12 tanks of 0.5 m³ volume for 8 weeks. Four replicates were made in each group, which were fed one of three diets containing fish oil (FO), soybean oil (SO) or lard oil (LO). The weight gain rate and specific growth rate did not differ among the groups (p > 0.05). Fish oil fish had the lowest condition factor (p < 0.05) and highest serum glucose content (p < 0.05). Crude lipid contents in the whole body and in the liver and muscle of FO fish were significantly lower than in the SO and LO groups (p < 0.05). The fatty acid composition of whole‐body lipids was closely correlated with that of the diet. The carnitine palmitoyltransferase 1 (cpt1) activity in the FO group was significantly higher than those in the SO and LO groups (p < 0.05). No significant differences in fatty acid synthase (fasn) activity were observed among the groups (p > 0.05). The Cpt1 and fasn gene expression levels in the FO group were significantly higher than those of the SO and LO groups (p < 0.05). The apolipoprotein B100 gene expression level was significantly higher in the SO group than in the FO group (p < 0.05). Fatty acid‐binding protein 1 gene expression levels in the FO and SO groups were not different (p > 0.05) but were both higher than that of the LO group (p < 0.05). The delta‐6 fatty acyl desaturase gene expression level in the LO group was significantly higher than that in the FO group (p < 0.05), but lower than that in the SO group (p < 0.05). It can be concluded that FO can be completely replaced by SO or LO in the M. salmoides diet, at least within the 8‐week culture period. Different types of dietary lipids significantly affect body condition and hepatic lipid metabolism in M. salmoides.     

Effects of alternative dietary oils on lipid metabolism and related gene expression in hybrid grouper (♀Epinephelus fuscoguttatus × ♂E. lanceolatu)

An 8‐week growth trial was conducted to evaluate effects of dietary oil sources on growth, enzymes activity and genes expression levels related to lipid metabolism of hybrid grouper (♀Epinephelus fuscoguttatus × ♂E. lanceolatu) juveniles. Seven iso‐lipid (97 g/kg of dry matter) and iso‐protein (503.5 g/kg of dry matter) experimental diets were formulated containing 50 g/kg fish oil (FO; acting as controls) or various vegetable oils (VOs): corn oil (CO), sunflower oil (SO), tea oil (TO), olive oil (OO), rice oil (RO) and mixed oil (MO; comprising equal amounts of these oils). Each diet was fed to triplicate groups of 40 fish for per repetition (15.09 ± 0.01 g) for 56 days. The results show that (a) alternative dietary oils had no significant effects on final weight compared with control group (p > .05); (b) compared with FO group, VOs significantly changed the contents of serum lipoproteins, cholesterol, triglycerides and the activity of liver lipid‐metabolizing enzymes (p < .05); (c) CO group had the least effect on the serum lipoproteins, triglycerides and cholesterol of grouper compared with control; the activity of liver lipid‐metabolizing enzymes in RO and control group was the closest; (d) the mRNA levels of Δ6 Fatty acid desaturase (Δ6Fad), hormone‐sensitive lipase (HSL) and lipoprotein lipase (LPL) were not significantly effected by lipid sources, but CO, TO, OO and MO significantly down‐regulated the expression of fatty acid synthetase (FAS) mRNA level in liver, while RO opposite (p < .05); (e) vegetable oil significantly up‐regulated peroxisome proliferator‐activated receptor α (PPARα) and peroxisome proliferator‐activated receptor β (PPARβ) mRNA levels, while TO and RO down‐regulated peroxisome proliferator‐activated receptor γ (PPARγ) mRNA levels (p < .05); and 6) MO significantly increased the mRNA levels of heart‐type fatty acid‐binding protein (H‐FABP) and adipocyte‐type fatty acid‐binding protein (A‐FABP) (p < .05), while other VOs had no effect on them (p > .05). In conclusion, dietary substitution of FO by VO in diet affected lipid metabolism of grouper, which may be regulated by PPARs.     

Differential expression of lipid metabolism‐related genes and miRNAs in Ctenopharyngodon idella liver in relation to fatty liver induced by high non‐protein energy diets

To explore the mechanism of fatty liver formation induced by high non‐protein energy diets in grass carp (Ctenopharyngodon idella), basal diet and high‐energy diets were fed to juvenile grass carp for 9 weeks. The experimental groups fed on high‐energy diets which included a high‐lipid diet (H‐LIP), a high‐carbohydrate diet (H‐CHO) and a high‐lipid and carbohydrate diet (H‐CL). The control group fed on basal diet. Growth performance, liver fat accumulation, serum biochemical indexes and the expression levels of lipid metabolism‐related genes (SREBP‐1, PPARγ, FAS, ACC1, and LPL) and miRNAs (miR‐33, miR‐122, and miR‐370) were examined at the end of the feeding trial. There were no significant differences in growth rate and feed efficiency among the four groups. However, significant increase in mesenteric and liver fat contents, and lipid droplets in the liver was induced by high‐lipid and high‐carbohydrate diets. There were significant differences in serum biochemical indicators such as AST/ALT, GLB, TG and TP, and liver fatty acid composition between the control and experimental groups. The expression levels of SREBP‐1, PPARγ, FAS, ACC1 and LPL were upregulated, while CPT‐1 was downregulated with the high‐energy treatments. Additionally, the expression levels of miR‐33, miR‐122 and miR‐370 in the liver were higher in the three high‐energy treatments than those in the control (P < 0.05). The results suggest that modifications of lipid metabolism‐related genes and miRNAs may be involved in fatty liver formation induced by high non‐protein energy diets in grass carp.