The protein-sparing effect of α -lipoic acid in juvenile grass carp, Ctenopharyngodon idellus : effects on lipolysis, fatty acid β -oxidation and protein synthesis

Study of carbonate alkalinity-induced hepatic tissue damage in Hefang crucian carp (Carassius auratus) based on transcriptomic analysis

This study investigated the effects of different sodium bicarbonate (NaHCO3) concentrations (0 g/L, 1 g/L, and 3 g/L) on Hefang crucian carp (12.0 ± 1.1 g) over a 96-hour period. The experiment is divided into three groups, each with three replicates, and each replicate contains 30 fish. We employed a comprehensive approach integrating histology, physiological and biochemical assays, transcriptomics, as well as artificial intelligence (AI)-assisted analysis. This multifaceted method allowed us to examine changes in gill and liver morphology, osmoregulation, antioxidant capacity, immune response, and physiological metabolism. Results showed that gill and liver tissue damage increased with rising water alkalinity. Serum sodium (Na+), potassium (K+), blood ammonia, and gill Na+/K+-ATPase (NKA) levels increased significantly (p < 0.05). Hepatic antioxidant enzymes initially increased, then decreased with prolonged stress. Serum and liver immunoenzyme indices were higher in bicarbonate-treated groups compared to controls. Carbonate treatment altered lipid and glucose metabolism in both serum and liver. Transcriptome analysis, enhanced by large language models (LLMs), revealed differentially expressed genes (DEGs) significantly associated with ion binding, transport, apoptosis, and metabolism. In conclusion, excessive carbonate intake in fish alters serum physiological functions and affects hepatic metabolic functions. Crucian carp primarily regulate hepatic antioxidant systems, utilize carbohydrate breakdown for energy requirements, and employ lipids in osmoregulation. This study provides insights into fish adaptation to saline-alkaline environments and offers support for the development of aquaculture in saline-alkaline waters.

Multiple effects of dietary supplementation with Lactobacillus reuteri and Bacillus subtilis on the growth, immunity, and metabolism of largemouth bass (Micropterus salmoides)

Probiotics play an essential role in the largemouth bass (Micropterus salmoides) aquaculture sector. They aid the fish in sickness prevention, intestinal structure improvement, food absorption, and immune system strengthening. In this experiment, Bacillus subtilis (BS, 107 CFU/g) and Lactobacillus reuteri (LR, 107 CFU/g) were added to the feed and then fed to M. salmoides for 35 days. The effects of two probiotics on the growth, immunity, and metabolism of M. salmoides organisms were studied. The results revealed that the BS group significantly increased the growth rate and specific growth rate of M. salmoides, while both the BS and LR groups significantly increase the length of villi M. salmoides intestines. The BS group significantly increased the levels of AKP, T-AOC, and CAT in the blood of M. salmoides, as well as AKP levels in the intestine. Furthermore, the BS group significantly increased the expression of intestinal genes Nrf2, SOD1, GPX, and CAT, while significantly decreasing the expression of the keap1 gene. M. salmoides gut microbial analysis showed that the abundance of Planctomycetota was significantly different in both control and experimental groups. Analyzed at the genus level, the abundance of Citrobacter, Paracoccus, Luedemannella， Sphingomonas, Streptomyces and Xanthomonas in the both control and experimental groups were significantly different. The BS group's differentially expressed genes were predominantly enriched in oxidative phosphorylation pathways in the intestine, indicating that they had a good influence on intestinal metabolism and inflammation suppression. In contrast, differentially expressed genes in the LR group were primarily enriched in the insulin signaling and linoleic acid metabolism pathways, indicating improved intestine metabolic performance. In conclusion, B. subtilis and L. reuteri improve the growth and health of M. salmoides, indicating tremendous potential for enhancing intestinal metabolism and providing significant application value.

Effect of tea polyphenol-trehalose complex coating solutions on physiological stress and flesh quality of marine-cultured Turbot Scophthalmus maximus during waterless transport

OBJECTIVE

The waterless transport of live fish has changed the present situation of live-fish transport. However, the waterless transport environment may cause stress in fish. This research evaluated the effect of tea polyphenol-trehalose (TPT) coating solutions on Turbot Scophthalmus maximus during waterless transport.

METHODS

After cold acclimation, Turbot were coated and subsequently transported in a waterless environment for 18 h. Physiological and biochemical parameters were measured, including lysozyme (LZM) and immunoglobulin M (IgM) activities, serum creatinine (Cr) and uric acid (UA) concentrations, and nutritional flavor.

RESULT

The results showed that the nonspecific immunity of Turbot was inhibited during the waterless transport; the LZM activity first increased and then decreased, and the serum Cr and UA concentrations significantly increased. In addition, the waterless transport promoted the breakdown of Turbot flesh proteins, leading to changes in nucleotides and free amino acids (FAAs). After waterless transport, the LZM and IgM activities in the TPT-treated Turbot were higher than those in the control group (CK), and the changes in FAA content and nucleotides were smaller than those observed in the CK group.

CONCLUSION

This study shows that the use of TPT coating solution can reduce the impact of waterless transportation stress on the immune and metabolic functions of Turbot and can maintain the meat quality and flavor of Turbot.

Pleurotus eryngii root waste and soybean meal co-fermented protein improved the growth, immunity, liver and intestinal health of largemouth bass (Micropterus salmoides)

The present study aimed to evaluate the effect of king oyster mushroom (Pleurotus eryngii) root waste and soybean meal co-fermented protein (CFP) on growth performance, feed utilization, immune status, hepatic and intestinal health of largemouth bass (Micropterus salmoides). Largemouth bass (12.33 ± 0.18 g) were divided into five groups, fed with diets containing 0 %, 5 %, 10 %, 15 % and 20 % CFP respectively for 7 weeks. The growth performance and dietary utilization were slightly improved by the supplementation of CFP. In addition, improved immunoglobulin M (IgM) content and lysozyme activity in treatments confirm the enhancement of immunity in fish by the addition of CFP, especially in fish fed 20 % CFP (P < 0.05). Furthermore, CFP significantly improved liver GSH (glutathione) content in groups D10 and D15 (P < 0.05), and slightly improved total antioxidant capacity (T-AOC), superoxide dismutase (SOD) activity while slightly reduced malondialdehyde (MDA) content. Simultaneously, the upregulation of lipolysis-related genes (PPARα, CPT1 and ACO) expression and downregulation of lipid synthesis-related genes (ACC and DGAT1) expression was recorded in the group D20 compared with the control (P < 0.05), which were consistent with the decreased liver lipid contents, suggests that lipid metabolism was improved by CFP. In terms of intestinal structural integrity, ameliorated intestinal morphology in treatments were consistent with the upregulated Occludin, Claudin-1 and ZO-1 genes expression. The intestinal pro-inflammatory cytokines (TNF-α and IL-8) expression were suppressed while the anti-inflammatory cytokines (IL-10 and TGF-β) were activated in treatments. The expression of antimicrobial peptides (Hepcidin-1, Piscidin-2 and Piscidin-3) and intestinal immune effectors (IgM and LYZ) were slightly up-regulated in treatments. Additionally, the relative abundance of intestinal beneficial bacteria (Firmicutes) increased while the relative abundance of potential pathogenic bacteria (Fusobacterium and Proteobacteria) decreased, which indicated that the intestinal microbial community was well-reorganized by CFP. In conclusion, dietary CFP improves growth, immunity, hepatic and intestinal health of largemouth bass, these data provided a theoretical basis for the application of this novel functional protein ingredient in fish.

The Role of Cholesterol during the Ovarian Maturation and Lipid Metabolism of Female Chinese Mitten Crab (Eriocheir sinensis)

In previous study, we found that the cholesterol requirement of Eriocheir sinensis was 0.27%, to further investigate the effects of cholesterol on health status, ovarian maturation, and lipid metabolism of female Eriocheir sinensis broodstock. Two diets containing 0% and 0.25% (actually 0.05% and 0.27%) cholesterol were fed to the female crabs (average weight: 49.21 ± 0.11 g) for 4 months and sampled once a month. The results showed that the body weight (BW), survival rate (SR), meat yield (MY), condition factor (CF), hepatosomatic index (HSI), and gonadosomatic index (GSI) of Eriocheir sinensis were significantly affected by treatment time and compared with the cholesterol deficient group, supplementing cholesterol significantly increased BW, HSI, and GSI (P < 0.05). In addition, long-term lack of cholesterol will lead to a significant decrease in the activity of ACP, AKP, and SOD and a significant increase in the content of MDA. The histological results showed that cholesterol significantly increased the volume of oocytes (P < 0.05). Further studies found that 0.27% cholesterol significantly increased the transcription levels of vtg and vgr in hepatopancreas and ovaries, which may be the main reason for the increase of oocyte size (P < 0.05). When fed with 0.27% cholesterol diet, the contents of nutrients in hepatopancreas and ovaries increased significantly, especially lipids and cholesterol (P < 0.05). Through the analysis of mRNA expression level of genes related to lipid metabolism, it was found that cholesterol enhanced the transcription level of genes related to lipid synthesis and transport in hepatopancreas, thereby promoting the accumulation of lipid in the organism. Furthermore, compared with control group, the levels of juvenile hormone (JH), 17β-estradiol (E2), methyl farnesoate (MF), and ecdysone in the organism were significantly increased after feeding a diet with 0.27% cholesterol (P < 0.05). In summary, supplementing an appropriate amount of cholesterol in the diet can improve the growth performance of Eriocheir sinensis broodstock, enhance the body's antioxidant and immune system, and promote the accumulation of nutrients in the ovaries, thereby promoting ovarian maturation.

The immunosuppressive, growth-hindering, hepatotoxic, and oxidative stress and immune related-gene expressions-altering effects of gibberellic acid in Oreochromis niloticus: A mitigation trial using alpha-lipoic acid

This study aimed to examine the effects of gibberellic acid (GBA) on growth, hemato-biochemical parameters related to liver functions, digestive enzymes, and immunological response in Oreochromis niloticus. Besides, the probable underlying mechanisms were explored by assessing antioxidant, apoptotic, and immune-related gene expression. Furthermore, the likelihood of restoration following alpha-lipoic acid (LIP) dietary supplementation was explored. The fish (average initial weight 30.75 ± 0.46) were equally classified into four groups: the control group, the LIP group (fed on a basal diet plus 600 mg/kg of LIP), the GBA group (exposed to 150 mg GBA/L), and the GBA + LIP group (exposed to 150 mg GBA/L and fed a diet containing LIP and GBA) for 60 days. The study findings showed that LIP supplementation significantly reduced GBA's harmful effects on survival rate, growth, feed intake, digestive enzymes, and antioxidant balance. Moreover, the GBA exposure significantly increased liver enzymes, stress markers, cholesterol, and triglyceride levels, all of which were effectively mitigated by the supplementation of LIP. Additionally, LIP addition to fish diets significantly minimized the histopathological alterations in the livers of GBA-treated fish, including fatty change, sharply clear cytoplasm with nuclear displacement to the cell periphery, single-cell necrosis, vascular congestion, and intralobular hemorrhages. The GBA-induced reduction in lysozyme activity, complement C3, and nitric oxide levels, together with the downregulation of antioxidant genes (cat and sod), was significantly restored by dietary LIP. Meanwhile, adding LIP to the GBA-exposed fish diets significantly corrected the aberrant expression of hsp70, caspase- 3, P53, pcna, tnf-a, and il-1β in O. niloticus liver. Conclusively, dietary LIP supplementation could mitigate the harmful effects of GBA exposure on fish growth and performance, physiological conditions, innate immunity, antioxidant capability, inflammatory response, and cell apoptosis.

Effect of Tea Polyphenols, α-Lipoic Acid and Their Joint Use on the Antioxidant and Lipid Metabolism Performance of Hybrid Grouper (♀Epinephelus fuscoguttatus × ♂E. lanceolatu) Fed with High-Lipid Diets

This study investigated tea polyphenols (TP), α-lipoic acid (ALA) and their joint use on the antioxidant and lipid metabolic performance of hybrid grouper (♀Epinephelus fuscoguttatus × ♂E. lanceolatu) took food with high-fat diets. Six high-lipid diets with isonitrogen (50% of dry matter) and isolipid (17% of dry value) were designed, in which a total content of 1,000 mg/kg additives were added to each group except for the control group (FL). The additives addition ratios in each group were ALA (AL), TP (PL), ALA : TP = 1 : 1 (EL), ALA : TP = 1 : 2 (OL), ALA : TP = 2 : 1 (TL). Each diet was divided into three repeat groups with 30 tails (6.84 ± 0.01 g) in each group and fed for 8 weeks. The consequences were as follows: (1) the highest weight gain rate, specific growth rate, as well as the lowest feed conversion ratio and ingestion rate were discovered in the OL team, which were opposite to the TL group. (2) The body fat content and muscle fat content in the fish oil group were the lowest (P < 0.05), while those of the TL group were the highest. (3) Serum catalase, glutathione peroxidase, total antioxidant capacity, and superoxide dismutase activities were the highest, and the content of reactive oxygen species was the lowest in the OL group. (4) The OL group has the highest hepatic lipase activity and the lowest very low-density lipoprotein content of the liver. In contrast, the TL group had the highest fatty acid synthetase (FAS) activity (P < 0.05). (5) The oil-red aspects of liver tissue displayed lipid particles in other groups were reduced to different degrees compared with FL group, and the OL group showed the best lipid-lowering effect. (6) Compared with the FL group, the relative expressions of FAS, acetyl-CoA carboxylase (acc), and apolipoprotein b-100 (apoB100) genes in the liver were decreased. The relative expressions of lipoprotein lipase (lpl) and peroxisome proliferators-activated receptors-α (pparα) genes related to lipid catabolism were increased, among which the OL group had the most significant change (P < 0.05). (7) According to the 7-day challenge test of Vibrio alginolyticus, the OL group had the highest survival rate. To sum up, both ALA and TP have positive effects on relieving the lipid metabolism disorder of hybrid grouper. If they are jointly used, adding ALA : TP in a ratio of 1 : 2 (OL) may have the best effect, and an addition ratio of 2 : 1 (TL) may inhibit the hybrid grouper growth and increase the feeding cost.

The Effects of Lipoic Acid on Yolk Nutrient Utilization, Energy Metabolism, and Redox Balance over Time in Artemia sp

Lipoic acid (LA) is a mitochondrial coenzyme that, depending on the concentration and exposure time, can behave as an antioxidant or pro-oxidant agent and has a proven ability to modulate metabolism by promoting lipid and glucose oxidation for energy production. To assess the effects of LA on energy metabolism and redox balance over time, Artemia sp. nauplii was used as an animal model. The administered concentrations of the antioxidant were 0.05, 0.1, 0.5, 1.0, 5.0, and 10.0 µM. Therefore, possible differences in protein, triglyceride, glucose, and lactate concentrations in the artemia samples and total ammoniacal nitrogen (TAN) in the culture water were evaluated. We also measured the effects of LA on in vivo activity of the electron transport system (ETS), antioxidant capacity, and production of reactive oxygen species (ROS) at 6, 12, 18, and 24 h post-hatching. There was a decrease in glucose concentration in the LA-treated animals, and a decrease in ammonia production was observed in the 0.5 µM LA treatment. ETS activity was positively regulated by the addition of LA, with the most significant effects at concentrations of 5.0 and 10.0 µM at 12 and 24 h. For ETS activity, treatments with LA presented the highest values at 24 h, a period when ROS production decreased significantly, for the treatment with 10.0 µM. LA showed positive regulation of energy metabolism together with a decrease in ROS and TAN excretion.

Effects of Dietary Alpha-Lipoic Acid on Growth Performance, Serum Biochemical Indexes, Liver Antioxidant Capacity and Transcriptome of Juvenile Hybrid Grouper (Epinephelus fuscoguttatus♀ × Epinephelus polyphekadion♂)

We aimed to investigate the effects of dietary alpha-lipoic acid (α-LA) on the growth performance, serum biochemical indexes, liver morphology, antioxidant capacity, and transcriptome of juvenile hybrid groupers (Epinephelus fuscoguttatus♀ × Epinephelus polyphekadion♂). Four experimental diets supplemented with 0 (SL0), 0.4 (L1), 0.6 (L2), and 1.2 (L3) g/kg α-LA were formulated and fed to three replicates of juvenile hybrid grouper (24.06 ± 0.15 g) for 56 d. The results indicated that dietary 0.4 and 0.6 g/kg α-LA significantly decreased the weight gain rate in juvenile hybrid groupers. Compared with SL0, the content of total protein in the serum of L1, L2, and L3 increased significantly, and alanine aminotransferase decreased significantly. The content of albumin in the serum of L3 increased significantly, and triglyceride, total cholesterol, and aspartate aminotransferase decreased significantly. In addition, the hepatocyte morphology in L1, L2, and L3 all showed varying degrees of improvement, and the activities of glutathione peroxidase and superoxide dismutase in the liver of L2 and L3 were significantly increased. A total of 42 differentially expressed genes were screened in the transcriptome data. KEGG showed that a total of 12 pathways were significantly enriched, including the pathway related to immune function and glucose homeostasis. The expression of genes (ifnk, prl4a1, prl3b1, and ctsl) related to immune were significantly up-regulated, and the expressions of gapdh and eno1 genes related to glucose homeostasis were significantly down-regulated and up-regulated, respectively. In summary, dietary supplementation of 0.4 and 0.6 g/kg α-LA inhibited the growth performance of juvenile hybrid groupers. A total of 1.2 g/kg α-LA could reduce the blood lipid level, improve hepatocyte damage, and increase the hepatic antioxidant enzyme activity. Dietary α-LA significantly affected the pathway related to immune function and glucose homeostasis.

High glucose induces apoptosis, glycogen accumulation and suppresses protein synthesis in muscle cells of olive flounder Paralichthys olivaceus

The effect and the mechanism of high glucose on fish muscle cells are not fully understood. In the present study, muscle cells of olive flounder (Paralichthys olivaceus) were treated with high glucose (33 mM) in vitro. Cells were incubated in three kinds of medium containing 5 mM glucose, 5 mM glucose and 28 mM mannitol (as an isotonic contrast) or 33 mM glucose named the Control group, the Mannitol group and the high glucose (HG) group, respectively. Results showed that high glucose increased the ADP:ATP ratio and the reactive oxygen species (ROS) level, decreased mitochondrial membrane potential (MMP), induced the release of cytochrome C (CytC) and cell apoptosis. High glucose also led to cell glycogen accumulation by increasing the glucose uptake ability and affecting the mRNA expressions of glycogen synthase and glycogen phosphorylase. Meanwhile, it activated AMP-activated protein kinase (AMPK), inhibited the activity of mammalian target of rapamycin (mTOR) signalling pathway and the expressions of myogenic regulatory factors (MRF). The expressions of myostatin-1 (mstn-1) and E3 ubiquitin ligases including muscle RING-finger protein 1 (murf-1) and muscle atrophy F-box protein (mafbx) were also increased by the high glucose treatment. No difference was found between the Mannitol group and the Control group. These results demonstrate that high glucose has the effects of inducing apoptosis, increasing glycogen accumulation and inhibiting protein synthesis on muscle cells of olive flounder. The mitochondria-mediated apoptotic signalling pathway, AMPK and mTOR pathways participated in these biological effects.

Optineurin promotes myogenesis during muscle regeneration in mice by autophagic degradation of GSK3β

Skeletal muscle regeneration is essential for maintaining muscle function in injury and muscular disease. Myogenesis plays key roles in forming new myofibers during the process. Here, through bioinformatic screen for the potential regulators of myogenesis from 5 independent microarray datasets, we identify an overlapping differentially expressed gene (DEG) optineurin (OPTN). Optn knockdown (KD) delays muscle regeneration in mice and impairs C2C12 myoblast differentiation without affecting their proliferation. Conversely, Optn overexpression (OE) promotes myoblast differentiation. Mechanistically, OPTN increases nuclear levels of β-catenin and enhances the T-cell factor/lymphoid enhancer factor (TCF/LEF) transcription activity, suggesting activation of Wnt signaling pathway. The activation is accompanied by decreased protein levels of glycogen synthase kinase 3β (GSK3β), a negative regulator of the pathway. We further show that OPTN physically interacts with and targets GSK3β for autophagic degradation. Pharmacological inhibition of GSK3β rescues the impaired myogenesis induced by Optn KD during muscle regeneration and myoblast differentiation, corroborating that GSK3β is the downstream effector of OPTN-mediated myogenesis. Together, our study delineates the novel role of OPTN as a potential regulator of myogenesis and may open innovative therapeutic perspectives for muscle regeneration.

Docosahexaenoic acid lessens hepatic lipid accumulation and inflammation via the AMP-activated protein kinase and endoplasmic reticulum stress signaling pathways in grass carp (Ctenopharyngodon idella)

The liver is the primary organ for frontline immune defense and lipid metabolism. Excessive lipid accumulation in the liver severely affects its metabolic homeostasis and causes metabolic diseases. Docosahexaenoic acid (DHA) is known for its beneficial effects on lipid metabolism and anti-inflammation, but its molecular mechanism remains unknown, especially in fish. In this study, we evaluated the protective effects of DHA on hepatic steatosis of grass carp (Ctenopharyngodon idella) in vivo and in vitro and mainly focused on the AMP-activated protein kinase (AMPK) and endoplasmic reticulum stress (ER stress) signaling pathway analysis. Grass carp were fed with purified diets supplemented with 0%, 0.5% and 1% DHA for 8 weeks in vivo. 1% DHA supplementation significantly decreased the liver triglyceride (TG), malondialdehyde (MDA), serum tumor necrosis factor α (TNFα) and nuclear factor kappa B (NFκB) contents. DHA administration suppressed ER stress and decreased the mRNA expressions related to hepatic inflammation and lipogenesis, accompanied by the activation of AMPK. Correspondingly, DHA activated the AMPK signaling pathway, and inhibited palmitic acid (PA)-evoked ER stress and lipid accumulation and inflammation of grass carp hepatocytes in vitro. In contrast, the inhibitor of AMPK (compound C, CC) abrogated the effects of DHA to improve PA-induced liver injury and ER stress. In conclusion, DHA inhibits ER stress in hepatocytes by the activation of AMPK and exerts protective effects on hepatic steatosis in terms of improving antioxidant ability, relieving hepatic inflammation and inhibiting hepatic lipogenesis. Our findings give a theoretical foundation for further elucidation of the beneficial role of DHA in vertebrates.

Mildronate triggers growth suppression and lipid accumulation in largemouth bass (Micropterus salmoides) through disturbing lipid metabolism

Many metabolic diseases in fish are often associated with lowered mitochondrial fatty acid β-oxidation (FAO). However, the physiological role of mitochondrial FAO in lipid metabolism has not been verified in many carnivorous fish species, for example in largemouth bass (Micropterus salmonids). In the present study, a specific mitochondrial FAO inhibitor, mildronate (MD), was used to investigate the effects of impaired mitochondrial FAO on growth performance, health status, and lipid metabolism of largemouth bass. The results showed that the dietary MD treatment significantly suppressed growth performance and caused heavy lipid accumulation, especially neutral lipid, in the liver. The MD-treated fish exhibited lower monounsaturated fatty acid and higher long-chain polyunsaturated fatty acids in the muscle. The MD treatment downregulated the gene expressions in lipolysis and lipogenesis, as well as the expressions of the genes and some key proteins in FAO without enhancing peroxisomal FAO. Additionally, the MD-treated fish had lower serum aspartate aminotransferase activity and lower pro-inflammation- and apoptosis-related genes in the liver. Taken together, MD treatment markedly induced lipid accumulation via depressing lipid catabolism. Our findings reveal the pivotal roles of mitochondrial FAO in maintaining health and lipid homeostasis in largemouth bass and could be hopeful in understanding metabolic diseases in farmed carnivorous fish.

Effects of dietary methionine on growth performance, muscle nutritive deposition, muscle fibre growth and type I collagen synthesis of on-growing grass carp (Ctenopharyngodon idella)

In the current research, a 60-d experiment was conducted with the purpose of exploring the impacts of methionine (Met) on growth performance, muscle nutritive deposition, muscle fibre growth and type I collagen synthesis as well as the related signalling pathway. Six diets (iso-nitrogenous) differing in Met concentrations (2·54, 4·85, 7·43, 10·12, 12·40 and 15·11 g/kg diets) were fed to 540 grass carp (178·47 (SD 0·36) g). Results showed (P < 0·05) that compared with Met deficiency, optimal level of dietary Met (1) increased feed intake, feed efficiency, specific growth rate and percentage weight gain (PWG); (2) increased fish muscle protein, lipid and free amino acid contents and improved fish muscle fatty acid profile as well as increased protein content in part associated with the target of rapamycin complex 1 (TORC1)/S6K1 signalling pathway; (3) increased the frequency distribution of muscle fibre with >50 µm of diameter; (4) increased type I collagen synthesis partly related to the transforming growth factor-β1/Smads and CK2/TORC1 signalling pathways. In conclusion, dietary Met improved muscle growth, which might be due to the regulation of muscle nutritive deposition, muscle fibre growth and type I collagen synthesis-related signal molecules. Finally, according to PWG and muscle collagen content, the Met requirements for on-growing grass carp (178-626 g) were estimated to be 9·56 g/kg diet (33·26 g/kg protein of diet) and 9·28 g/kg diet (32·29 g/kg of dietary protein), respectively.

Akt1/mTORC1 signaling modulates adaptive immune response of Nile tilapia by promoting lymphocyte activation and proliferation

Serving as a significant signaling molecule, RAC-alpha serine/threonine-protein kinase (Akt1) plays indispensable roles in cell cycle, growth, survival, metabolism, as well as immune response. However, how Akt1 regulates adaptive immune response in early vertebrate, especially the teleost, is largely unknown. Here, using a Nile tilapia Oreochromis niloticus model, we investigated the regulatory role of Akt1 in adaptive immunity of teleost. Both sequence and structure of the O. niloticus Akt1 (OnAkt1), were evolutionarily conserved comparing with the counterparts from other vertebrates. mRNA of OnAkt1 was widely expressed in lymphoid organs/tissues of Nile tilapia, with relative higher level in PBL. After Nile tilapia was infected by Aeromonas hydrophila, both transcription and phosphorylation levels of OnAkt1 were obviously elevated in spleen lymphocytes at the adaptive immune stage, suggesting Akt1 participated in primary adaptive immune response of Nile tilapia. Furthermore, OnAkt1 transcript or phosphorylation was dramatically augmented after spleen lymphocytes were activated by T cell specific mitogen PHA or lymphocyte agonist PMA. More critically, inhibition of Akt1 by specific inhibitor crippled the activation of downstream mTORC1 signaling, and impaired the up-regulation of T cell activation markers CD44, IFN-γ and CD122 in spleen lymphocytes upon PHA-induced T cell activation. Meanwhile, blockade of Akt1-activated mTORC1 signaling also decreased the frequency of BrdU⁺ lymphocytes during A. hydrophila infection, indicating the critical role of Akt1 in regulating lymphocyte proliferation of Nile tilapia. Together, our results demonstrated that Akt1 modulated adaptive immune response of Nile tilapia by promoting lymphocyte activation and proliferation via mTORC1 signaling. Our study enriched the regulatory mechanism of lymphocyte-mediated adaptive immunity in teleost, and thus provided novel insights into the evolution of adaptive immune system.

Interactions between dietary lipid levels and chronic exposure of legal aquaculture dose of sulfamethoxazole in juvenile largemouth bass Micropterus salmoides

Antibiotics have been widely used (mainly mixed with feed) in aquaculture, while few studies have evaluated the interactions between feed composition and antibiotics. Sulfamethoxazole (SMX) is a fat-soluble antibiotic, an eight weeks feeding trial was conducted to investigate the interactions between dietary lipid levels and chronic exposure of legal aquaculture dose of sulfamethoxazole in juvenile largemouth bass Micropterus salmoides, and evaluated the possible human health risk. Six practical diets were formulated to three levels of crude lipid (11, 14.5, 18 %) and two levels of SMX (0 and 0.3 %), namely low fat (LF), moderate fat (MF), high fat (HF), low fat and SMX (LFS), moderate fat and SMX (MFS), high fat and SMX (HFS), respectively. Each diet was assigned to three tanks (20 fish per tank, average weight 30.65 ± 0.02 g). Growth and organ indices were increased by SMX. Higher malformation rate and lower hypoxia stress resistance were found in fish exposed to SMX than those not exposed. Cholesterol and bile acid synthesis related gene expressions were down-regulated by SMX exposure. Oxidative stress, inflammation and apoptosis were increased in fish exposed to SMX. Significant interactions between dietary lipid levels and SMX on renal immune response of fish were observed. Remarkable damage of intestinal histology was observed in fish fed the diet HFS. In addition, dietary SMX exposure increased pathogen susceptibility of largemouth bass and induced dysbiosis of gut microbiota. The concentrations of SMX in muscle of fish fed diets containing SMX were higher than those fed other diets, and close to the maximum residue limit (MRL) in China and international organizations. Although chronic legal aquaculture dose of dietary SMX also increased the target hazard quotient (THQ) and estimated daily intake (EDI), there is no health risk in adults and children consuming fish filet.

Systemic effect of dietary lipid levels and α-lipoic acid supplementation on nutritional metabolism in zebrafish (Danio rerio): focusing on the transcriptional level

Considering the excessive lipid accumulation status caused by the increased dietary lipid intake in farmed fish, this study aimed to investigate the systemic effect of dietary lipid levels and α-lipoic acid supplementation on nutritional metabolism in zebrafish. A total of 540 male zebrafish (0.17 g) were fed with normal (CT) and high lipid level (HL) diets for 6 weeks, then fed on 1000 mg/kg α-lipoic acid supplementation diets for the second 6 weeks. HL diets did not affect whole fish protein content, but increased ASNS expression (P < 0.05). Dietary α-lipoic acid increased whole fish protein content, and decreased the expressions of protein catabolism-related genes in muscle of high lipid level groups (P < 0.05). Furthermore, HL diets increased the whole fish lipid content and the expressions of gluconeogenesis and lipogenesis-related genes (P < 0.05), and α-lipoic acid counteracted these effects and decreased the whole fish triglyceride and cholesterol contents and expressions of lipogenesis-related genes, with the enhanced expressions of lipolytic genes, especially in high lipid groups (P < 0.05). HL diets did not affect hepatocyte mitochondrial quantity or the mRNA expressions of mitochondrial biogenesis and electron transport chain-related genes; they were significantly increased by dietary α-lipoic acid (P < 0.05). These results indicated that high dietary lipid promotes lipid accumulation, while α-lipoic acid increases protein content in association of enhanced lipid catabolism. Thus, dietary α-lipoic acid supplementation could reduce lipid accumulation under high lipid, which provides a promising new approach in solving the problem of lipid accumulation in farmed fish.

Cinnamaldehyde improves the growth performance and digestion and absorption capacity in grass carp (Ctenopharyngodon idella)

The present study evaluated the effect of cinnamaldehyde (CIN) on the growth performance and digestion and absorption capacity of grass carp (Ctenopharyngodon idella). Fish were fed five diets including graded levels of CIN for 60 days. The results indicated that (1) appropriate CIN supplementation increased the growth performance and promoted the intestine growth of grass carp; (2) dietary appropriate CIN supplementation increased the digestion and absorption capacity by increasing the activities of intestinal and hepatopancreas digestive enzymes (lipase, chymotrypsin, trypsin, and amylase) and intestinal brush border enzymes (creatine kinase (CK), Na⁺/K⁺-ATPase, γ-glutamyl transpeptidase (γ-GT), and alkaline phosphatase (AKP)); (3) dietary CIN increased the absorption capacity which may be associated with the upregulated messenger RNA (mRNA) abundances of their amino acid transporters (AATs) in the intestine, which might be associated with activating the target of rapamycin (TOR) signaling pathway. The best CIN supplementation in the diets of grass carp was estimated to be 76.40 mg kg^-1 diet based on the best percent weight gain (PWG). In general, CIN increased the digestion and absorption capacity of grass carp and raised the mRNA abundances of AATs which may be partly related to activation of the TOR signaling pathway.

Feeding Faba Beans (Vicia faba L.) Reduces Myocyte Metabolic Activity in Grass Carp (Ctenopharyngodon idellus)

In this study, we aimed to explore the effects of faba bean (Vicia faba L.) on the energy metabolism of grass carp (Ctenopharyngodon idellus). A total of 180 fish (∼2900 g) were randomly assigned to six tanks (2.5 × 2.5 × 1.2 m; 30 individuals per tank) and fed either faba bean (Vicia faba L.) or a commercial diet for 120 days (3% body weight, twice per day). The results showed that faba bean-fed grass carp (FBFG) had significantly lower growth and higher fat accumulation in the mesenteric adipose tissue and hepatopancreas than commercial diet-fed grass carp (CDFG). Compared with CDFG, FBFG exhibited no significant difference in proximate composition of the muscle; however, an obvious decrease in muscle fiber size and significantly higher hardness, chewiness, and gumminess were observed. Transcriptome results showed that a total of 197 genes were differentially regulated in the dorsal muscle. Down-regulated genes included four genes annotated with myocyte development and 12 transcripts annotated with components of myofibrils. In addition, the FBFG group exhibited significantly lower expression of genes associated with oxygen transport, the mitochondrial respiratory chain, and creatine metabolism, suggesting reduced energy availability in the muscle of the FBFG. Moreover, using western-blotting and enzyme assays, we found decreased protein levels in the mitochondrial electron transport respiratory chain and creatine metabolism activities, as well as increased expression of autophagy marker protein levels, in the muscle of FBFG. Overall, our results suggest that an abnormal energy distribution may exist in grass carps after feeding with faba bean, which is reflected by a mass of fat deposition in the adipose tissue and hepatopancreas and subdued metabolic activity in the muscle.

The comparisons in protective mechanisms and efficiencies among dietary α-lipoic acid, β-glucan and l-carnitine on Nile tilapia infected by Aeromonas hydrophila

Dietary α-lipoic acid (LA), β-glucan (Gluc) and l-carnitine (L-Ca) are commonly used additives to promote fish growth and stress resistance in aquaculture production. However their mechanisms and efficiencies in helping fish to resist diseases have not been compared before. In this study, we fed Nile tilapia (Oreochromis niloticus) with diets containing appropriate doses of LA, Gluc and L-Ca for five weeks and further intraperitoneally injected the fish with Aeromonas hydrophila. After dietary treatment, none of the additives affected the fish growth, but dietary Gluc and L-Ca reduced protein and lipid body contents in fish, respectively. After A. hydrophila challenge, all fish treated with the three dietary additives showed higher survival rate, but those fed on dietary L-Ca had lower survival than those fed on LA and Gluc diets, indicating high protection efficiency of LA and Gluc. The protective mechanisms of the three feed additives were quite different under A. hydrophila infection. Dietary LA induced higher total antioxidant capacity and higher mRNA expression of anti-oxidative genes than other additives in liver and also activated partly the immune function in serum and spleen. Gluc largely increased the immune function by activating the immunity enzymes in serum, inducing inflammation in liver and increasing the expression of immune genes in spleen and head kidney. Gluc also increased partly the antioxidant capacity in serum and liver and lipid catabolism in liver. L-Ca largely increased lipid catabolism in liver while it increased partly the antioxidant capacities in serum and liver. Taken together, these results indicate that, dietary LA, Gluc and L-Ca have various protective mechanisms and differ in their efficiencies on resisting A. hydrophila infection in Nile tilapia.