Excessive Dietary Lipid Affecting Growth Performance, Feed Utilization, Lipid Deposition, and Hepatopancreas Lipometabolism of Large-Sized Common Carp (Cyprinus carpio)

Effects of Dietary Lipid Levels on the Growth, Muscle Fatty Acid and Amino Acid Composition, Antioxidant Capacity, and Lipid Deposition in Mirror Carp (Cyprinus carpio)

In fish, increasing the crude lipid level of feed can save protein and improve feed utilization. Mirror carp (Cyprinus carpio) is one of the most widely farmed fish species in the world. In this study, mirror carp larvae were fed isonitrogenous diets with different lipid levels (3%, 5%, 7%, 9%, 11%, and 13%). The rearing trial lasted for eight weeks. The results revealed that when the fat content was 9%, the AWGR, WGR, and FCR were highest, whereas FCR was lowest. The AWGR was correlated with the dietary lipid level, and the regression equation was y = -2.312x2 + 45.01x + 214.49. Compared with those in the control group, the T-CHO and TG contents were significantly greater in the 13% lipid content groups and significantly lower in the 9% lipid content groups (p < 0.05). In terms of muscle quality, the contents of MUFAs, PUFAs, and DHA + EPA were significantly greater than those in the other experimental groups (p < 0.05). Oil red O staining revealed a lipid content of 13% with severe fat deposition. In addition, the results of the analysis of antioxidant enzyme activity revealed that the activities of GSH, CAT and T-AOC were significantly greater at the 9% lipid content, and that the MDA content was significantly greater at the 13% lipid content (p < 0.05). Similarly, the mRNA levels of GH, IGF-I, FAS, and LPL were significantly highest at a lipid level of 9% (p < 0.05). The above results revealed that the optimal dietary lipid requirement for the fast growth of mirror carp (6.86 ± 0.95 g) was 9.74% on the basis of nonlinear regression analysis of the AWGR. The dietary lipid level (9%) improved the growth, stress resistance, and lipid utilization of mirror carp to a certain extent.

Liver transcriptome and physiological analyses preliminarily revealed the adaptation mechanisms of Amur grayling (Thymallus arcticus grubei, Dybowski, 1869) fry for dietary lipid nutrition

The Amur grayling (Thymallus arcticus grubei Dybowski, 1869), a species of potentially economic and research value, is renowned for its tender meat, exquisite flavor, and high nutritional contents. This study was conducted to investigate the physiological adaptation mechanisms to dietary lipids in Amur grayling fry (with average initial weight 4.64±0.03 g). This study involved a 56-day feeding trial with diets containing varying lipid levels (9.07%, 12.17%, 15.26%, 18.09%, 21.16%, and 24.07%, designated as GL1 through GL6, respectively) to explore the impact of dietary lipids on growth performance, intestinal digestion, liver antioxidative function, and transcriptomic profiles. Results showed that The group receiving 18% dietary lipid exhibited a markedly higher weight gain rate (WGR) and specific growth rate compared to other groups, alongside a reduced feed conversion ratio (FCR), except in comparison to the 15% lipid group. Activities of lipase in pancreatic secretion and amylase in stomach mucosa peaked in the 18% lipid treatment group, indicating enhanced digestive efficiency. The liver of fish in this group also showed increased activities of antioxidative enzymes and higher levels of glutathione and total antioxidative capacity, along with reduced malondialdehyde content compared to the 9% and 24% lipid treatments. Additionally, serum high-density lipoprotein cholesterol levels were highest in the 18% group. Transcriptomic analysis revealed four significant metabolic pathways affected: Cholesterol metabolism, Fat digestion and absorption, PPAR signaling, and Fatty acid degradation, involving key genes such as Lipase, Lipoprotein lipase, Fatty acid-binding protein, and Carnitine palmitoyltransferase I. These findings suggest that the liver of Amur grayling employs adaptive mechanisms to manage excessive dietary lipids. Quadratic regression analysis determined the optimal dietary lipid levels to be 16.62% and 16.52%, based on WGR and FCR, respectively. The optimal dietary lipid level for juvenile Amur grayling appears to be around 18%, as evidenced by improved growth performance, digestive function, balanced serum lipid profile, and enhanced liver antioxidative capacity. Exceeding this lipid threshold triggers both adaptive and potentially detrimental liver responses.

Mitigation of cold stress in Nile tilapia (Oreochromis niloticus) through dietary lipids supplementation: a preliminary network meta-analysis

There is a growing body of evidence suggesting that water temperature can significantly impact the dietary fatty acid requirements of Nile tilapia (Oreochromis niloticus). Therefore, this study assessed the effectiveness of different dietary lipid sources on the growth performance of Nile tilapia reared at suboptimal temperatures. A network meta-analysis was performed, including searches of PubMed and Scopus from inception to January 2022, for trials that evaluated the effects of lipid sources on cold-stressed Nile tilapia. The Bayesian hierarchical framework was used to pool and compare the effect sizes of growth parameters such as weight gain, feed intake, and feed conversion ratio (FCR). Furthermore, the surface under the cumulative ranking curve (SUCRA) was obtained to calculate the probability that each lipid source was the most effective against cold stress. All subsequent numbers refer to comparisons with diets containing only fish oil. Dietary Aurantiochytrium significantly increased weight gain (SMD = 2.00, CrI: 0.70 to 3.40). In contrast, diets containing coconut oil led to significantly lower weight gain (SMD = - 3.30, CrI: - 6.00 to - 0.63) and higher FCR (SMD = 17.0, CrI: 6.70 to 27.0). Additionally, dietary corn oil was associated with a decrease in feed intake (SMD = - 2.32, CrI: - 3.91 to - 0.80), while a combination of fish and corn oil reduced FCR (SMD = - 5.70, CrI: - 11.0 to - 0.81). In general, the analysis of SUCRA values revealed that in cold-stressed Nile tilapia, Aurantiochytrium, sunflower oil, and the combination of fish and corn oil were the most effective lipid sources for improving growth at suboptimal temperatures. The results of the current study can serve as a basis for future studies that focus on the use of dietary lipid sources to mitigate cold stress in Nile tilapia.

High-fat-diet induced inflammation and apoptosis via activation of Ire1α in liver and hepatocytes of black seabream (Acanthopagrus schlegelii)

The present study aimed to reveal the role of inositol-requiring enzyme 1α (Ire1α) in mediating high-fat-diet (HFD) induced inflammation and apoptosis in fish and elucidate underling mechanisms of action. In experiment 1, black seabream juveniles were fed a control diet (Control, 12 % dietary lipid) or a high fat diet (HFD, 19 % dietary lipid) for eight weeks. In experiment 2, primary hepatocytes were isolated from black seabream juveniles and treated with oleic acid (OA, 200 μmol/L), OA + transfection with non-silencing control siRNA (negative control) (OA + NC), and OA + transfection with ire1α-small interfering RNA (OA + siire1α) for 48 h versus untreated (Control). Results indicated that fish fed HFD increased lipid deposition in the liver and caused hepatic steatosis. HFD group had significantly higher ire1α/Ire1α mRNA and phosphorylated protein expression and endoplasmic reticulum stress (ERS) related genes expression compared to the Control group, indicating that ERS was triggered. Meanwhile, feeding HFD induced inflammation and apoptosis by evaluated nuclear factor kappa B (nf-κb) mRNA and phosphorylated Nf-κb p65 protein expression, and c-Jun N-terminal kinase (jnk) mRNA and protein expression. However, knock down of ire1α (OA + siire1α) in primary hepatocytes alleviated OA-induced increased expression of ire1α/Ire1α mRNA and protein expression, nf-κb/Nf-κb p65 mRNA and phosphorylated protein expression, and jnk/Jnk mRNA and phosphorylated protein expression. These findings revealed the underling mechanism of action of HFD in fish, confirming that HFD increased ESR stress and Ire1α that, in turn, activated Nf-κb and Jnk pathways in hepatocytes and liver mediating HFD-induced inflammation and apoptosis.

Integrated Metabolome and Transcriptome Analyses Reveal the Efficacy of Steroidal Saponins for Glucose and Lipid Metabolism in Hybrid Grouper (♀Epinephelus fuscoguttatus × ♂Epinephelus lanceolatu) Fed Higher-Lipid Diets

An analysis of the extent of the effect of steroidal saponin addition on glucose and lipid metabolism in hybrid grouper liver was performed at the transcriptomic and metabolomic levels. Feeds (52% crude protein, 14% crude lipid) were prepared containing 0% (S0), 0.1% (S0.1), and 0.2% (S0.2) steroidal saponins. After eight weeks of feeding trial, compared to the S0 group, the activities of serum albumin, alanine aminotransferase, and aspartate transaminase were significantly lower and the activities of lysozyme, acid phosphatase, and alkaline phosphatase were significantly higher in the S0.1 group (p < 0.05). The superoxide dismutase, catalase, and glutathione peroxidase activities in the livers of the S0.1 group were significantly higher than those of the S0 group, while the malondialdehyde content was significantly lower than that of the S0 group (p < 0.05). There were forty-two differentially expressed genes and thirty-two differential metabolites associated with glucose and lipid metabolism enriched using KEGG and GO. In the S0 group, the expression of prostaglandin-endoperoxide synthase 1, prostaglandin E synthase 1, and thromboxane-2 synthase mRNA was significantly higher than in the S0.1 group (p < 0.05). The expression levels of genes in the S0 group were significantly higher than those in the S0.1 group (p < 0.05), including for glycogen synthase kinase, glucose-6-phosphatase catalytic subunit 2, fructose-1,6-bisphosphatase, phosphoenolpyruvate carboxykinase, glucose transporter 4, and malate dehydrogenase. The expression of mRNA such as fatty acid synthase, acetyl-CoA carboxylase, and sterol regulatory element-binding protein 1 was significantly lower in the S0.1 group than in the S0 group, while the expression of carnitine acyltransferase 1, acyl-CoA synthetase, and acyl-CoA dehydrogenase genes was significantly higher in the S0 group (p < 0.05). In summary, glycogen synthesis, gluconeogenesis, and the arachidonic acid metabolism pathway were inhibited by 0.1% steroidal saponins, and glycogenolysis, glycolysis, the tricarboxylic acid cycle, and the fatty acid β-oxidation pathway were activated. This study aims to provide a reference for the formulation of grouper feeds with a higher crude-lipid level.

Exercise training combined with a high-fat diet improves the flesh flavour, texture and nutrition of gibel carp (Carassius auratus gibelio)

To meet the consumer demand for high-quality flesh sources, this study investigated the impacts of exercise training (ET) combined with a high-fat diet (HFD) on flesh quality. The results showed that HFD increased muscular fat content but reduced hardness, flexibility and adhesiveness. ET decreased fat content but increased flesh water holding capacity, hardness and stickiness. In terms of flavour, ET decreased the umami and sweet amino acid contents, which were restored when concomitantly feeding the HFD. Metabolomics further revealed that ET and HFD mainly affect the alanine, aspartate and glutamate metabolism, the citrate cycle and purine metabolism. The E-nose and volatile metabolomics analysis demonstrated that the combination of ET and HFD improved the aroma of flesh by enhancing the content of key flavour compounds within flesh such as hexadecenoic acid, ethyl ester and methyl stearate. This research provides a new strategy for improving the flesh quality of cultured fish.

Tea Tree Oil Mediates Antioxidant Factors Relish and Nrf2-Autophagy Axis Regulating the Lipid Metabolism of Macrobrachium rosenbergii

Both oxidative stress and autophagy refer to regulating fat metabolism, and the former affects autophagy, but the role and mechanism of the antioxidant-autophagy axis in regulating lipid metabolism remains unclear. As an antioxidant, tea tree oil (TTO) has little research on the regulatory mechanism of lipid metabolism in crustaceans. This study investigated whether TTO could alter hepatopancreatic lipid metabolism by affecting the antioxidant-autophagy axis. Feed Macrobrachium rosenbergii with three different levels of TTO diets for 8 weeks: CT (0 mg/kg TTO), 100TTO (100 mg/kg TTO), and 1000TTO (1000 mg/kg TTO). The results showed that 100TTO treatment reduced the hemolymph lipids level and hepatopancreatic lipid deposition compared to CT. In contrast, 1000TTO treatment increased hepatopancreatic lipid deposition, damaging both morphology and function in the hepatopancreas. The 100TTO treatment promoted lipolysis and reduced liposynthesis at the transcriptional level compared to the CT group. Meanwhile, it improved the hepatopancreas antioxidant capacity and maintained mitochondrial structural and ROS homeostasis. In addition, it simultaneously activated the expression of transcription factors Keap1-Nrf2 and Imd-Relish. By contrast, the 1000TTO group significantly enhanced the ROS level, which considerably activated the Keap1-Nrf2 signaling expression but had no significant effects on the expression of Imd-Relish. The 100TTO group supplementation significantly enhanced lipid droplet breakdown and autophagy-related genes and protein expression. On the contrary, the 1000TTO group significantly inhibited the expression of genes and proteins related to autophagy. Pearson analysis revealed that Nrf2 has a positive correlation to lipid anabolism-related genes (Fasn, Srebp1, Pparγ) and autophagy regulators (mtor, akt, p62), and were negatively correlated with lipolysis-related genes (Cpt1, Hsl, Ampkα) and autophagy markers (Ulk1, Lc3). Relish was positively correlated with Atgl, Cpt1, Ampkα, Ulk1, and Lc3, and negatively correlated with Pparγ and p62. Moreover, Keap1 and Imd were negatively correlated with p62 and mtor, respectively. In sum, 100 mg/kg TTO enhanced antioxidant activity and increased autophagy intensity through the Relish-Imd pathway to enhance lipid droplet breakdown, while 1000 mg/kg TTO overexpressed Nrf2, thus inhibiting autophagy and ultimately causing excessive lipid deposition and peroxidation. Our study gives a fresh perspective for deciphering the bidirectional regulation mechanism of lipid metabolism by different doses of TTO based on the antioxidant-autophagy axis.

Hepatic Transcriptome Analysis Provides New Insight into the Lipid-Reducing Effect of Dietary Taurine in High-Fat Fed Groupers (Epinephelus coioides)

A transcriptome analysis was conducted to provide the first detailed overview of dietary taurine intervention on liver lipid accumulation caused by high-fat in groupers. After an eight-week feeding, the fish fed 15% fat diet (High-fat diet) had higher liver lipid contents vs. fish fed 10% fat diet (Control diet). 15% fat diet with 1% taurine (Taurine diet) improved weight gain and feed utilization, and decreased hepatosomatic index and liver lipid contents vs. the High-fat diet. In the comparison of the Control vs. High-fat groups, a total of 160 differentially expressed genes (DEGs) were identified, of which up- and down-regulated genes were 72 and 88, respectively. There were 49 identified DEGs with 26 and 23 of up- and down-regulated in the comparison to High-fat vs. Taurine. Several key genes, such as cysteine dioxygenase (CDO1), ADP-ribosylation factor 1/2 (ARF1_2), sodium/potassium-transporting ATPase subunit alpha (ATP1A), carnitine/acylcarnitine translocase (CACT), and calcium/calmodulin-dependent protein kinase II (CAMK) were obtained by enrichment for the above DEGs. These genes were enriched in taurine and hypotaurine metabolism, bile secretion, insulin secretion, phospholipase D signaling pathway, and thermogenesis pathways, respectively. The present study will also provide a new insight into the nutritional physiological function of taurine in farmed fish.