Large Yellow Croaker Larimichthys Crocea Research Articles

Effects of antimicrobial peptide APSH‐07 on the growth performance, anti‐oxidation responses, stress resistance and intestine microbiota in large yellow croakerLarimichthys crocea

A 65‐day feeding trial was conducted to investigate the effects of dietary antimicrobial peptide APSH‐07 on the growth performance, anti‐oxidation responses, stress resistance and intestine microbiota of large yellow croaker Larimichthys crocea. Four isonitrogenous and isolipidic diets were formulated with 0, 30, 60 and 90 mg/kg of APSH‐07, respectively. The results showed that the fish fed with 90 mg/kg of dietary APSH‐07 had the significantly highest specific growth rate (p < .05). The activities of catalase, superoxide dismutase, the total anti‐oxidative capacity and lysozyme had the significantly highest values in liver of fish fed with 90 mg/kg of dietary APSH‐07 (p < .05). Serum glucose increased significantly in fish fed diets without APSH‐07 supplementation after temperature stress, while serum cortisol increased significantly in those after trawl stress (p < .05). Fish fed with 90 mg/kg of dietary APSH‐07 showed significantly higher operational taxonomic units, ACE estimator and phylogenetic diversity whole tree in intestine microbiota compared to fish fed without APSH‐07 (p < .05). In conclusion, under the present experimental condition, 90 mg/kg of antimicrobial peptide APSH‐07 supplementation in diet had the better growth performance, higher anti‐oxidation and stress resistance capacity, and a potentially more beneficial intestine microbial community of large yellow croaker.

TRAF3 enhances TRIF-mediated signaling via NF-κB and IRF3 activation in large yellow croaker Larimichthys crocea

As a member of tumor necrosis factor receptor (TNFR)-associated factor (TRAF) family, TRAF3 is an important regulator of NF-κB and type I interferon (IFN) activation, especially in Toll-like receptors (TLRs)- and retinoic acid inducible gene I (RIG-I)-like receptors (RLRs)-mediated signaling pathway. In the present study, a TRAF3 homologue named Lc-TRAF3 was characterized in large yellow croaker (Larimichthys crocea). The open reading frame (ORF) of Lc-TRAF3 contains 1788 bp encoding a protein of 595 amino acids (aa). Sequence analysis indicated that Lc-TRAF3 is conserved in vertebrates, constituted with a N-terminal RING finger, two TRAF-type zinc fingers, and a C-terminal TRAF-MATH domain. The genome organization of Lc-TRAF3 is conserved in fish, with 13 exons and 12 introns, but different from that in birds or mammals, which contains 10 exons and 9 introns. Lc-TRAF3 was identified as cytosolic protein base on fluorescence microscopy analysis. Expression analysis revealed that Lc-TRAF3 was broadly distributed in examined organs/tissues, with the highest expression level in gill and weakest in brain, and could be up-regulated under poly I:C, LPS, PGN, and Pseudomonas plecoglossicida stimulation in vivo. Interestingly, overexpression Lc-TRAF3 could induce the activation of NF-κB, and Lc-TRAF3 co-transfected with Lc-TRIF induced a significantly higher level of NF-κB and IRF3 promoter activity, implying that Lc-TRAF3 may function as an enhancer in Lc-TRIF-mediated signaling pathway.

Liver transcriptome analysis reveals the molecular responses to low-salinity in large yellow croaker Larimichthys crocea

The large yellow croaker Larimichthys crocea is a euryhaline marine fish with wide consumptions and high commercial values in China. Low-salinity culture of L. crocea has been proposed to suppress the pathogens with low cost. However, the responses of L. crocea at molecular level to low salinity have not been fully understood. In this study, Illumina RNA-seq gene expression system was applied to globally screen the genes and pathways involved in the responses in liver tissues of L. crocea to low-salinity conditions. Compared with the control (24 ppt), a total of 1369, 685, 2980 and 3469 differentially expressed genes (DEGs) were identified in low-salinity treatments (8, 6, 4 and 2 ppt) for 40 days, respectively. Among them, 164 DEGs were common in 4 low-salinity groups. According to the KEGG pathway analysis, the DEGs were involved in material metabolism (carbohydrate, protein, and lipid metabolism), energy metabolism, growth, immune system, signal transduction, transcription and translation, and apoptosis. With respect to metabolism, up-regulated oxidative phosphorylation was the primary enriched pathways in response to low salinities of 6 ppt (S6) and 4 ppt (S4). The salinities of 8 ppt (S8) and 2 ppt (S2) were characterized by enhanced anabolism and inhibited material and energy metabolism, respectively. Concerning immune responses, innate immunity was promoted in S6 and S4 groups as a general stress response. L. crocea cultured in S4 group suffered few immune and inflammation risks, indicated by the negative responses to CD209 antigen (CD209) and C-reactive protein (crp). Moreover, low salinities induced higher absolute weight gain rate (AWGR) and survival rate of L. crocea, and S4 group presented the highest AWGR and survival rate. Our findings indicated that salinity of 4 ppt was preferable for the low-salinity farming of L. crocea. Overall, this work provides new insights into the molecular responses of L. crocea to low-salinity and references for L. crocea culture in low salinities.

Effects of replacement of dietary fish oil by rapeseed oil on growth performance, anti-oxidative capacity and inflammatory response in large yellow croaker Larimichthys crocea

A 12-week feeding trial was conducted to evaluate the effects of replacement of dietary fish oil by rapeseed oil on the growth, anti-oxidative capacity and inflammatory responses of large yellow croaker Larimichthys crocea (initial body weight: 36.02 ± 0.58 g). The control diet was designed to contain 6.5% of fish oil, and named as FO. Based on it, the fish oil was 50% and 100% replaced by rapeseed oil to make the other two diets (FR and RO, respectively). Results showed that the specific growth rate was significantly reduced, and the crude lipid contents in muscle and liver were significantly increased in the RO group. The total anti-oxidative capacity and expressions of superoxide dismutase 1 and 2, glutathion peroxidase and nuclear factor erythroid 2-related factor 2 in liver of fish fed RO were significantly lower. Dietary rapeseed oil significantly decreased expressions of arginase I and interleukin 10, and increased expressions of TNFα, interleukin 1β, toll-like receptor 22 and myeloid differentiation factor 88 in liver. In conclusion, high dietary rapeseed oil could suppress growth performance and liver anti-oxidative capacity, and induce inflammation of large yellow croaker.

Transcriptomic Analysis of the Cold-Pretreated Larimichthys crocea Showing Enhanced Growth Fitness in Cold Water.

The large yellow croaker Larimichthys crocea is an economically important marine fish species endemic to China and East Asia. Ningde area of Fujian Province is a major L. crocea aquaculture and spawning center in China. L. crocea cultivated at the Zhoushan area appears to be popular but suffered high mortality in cold water during winter seasons. To reduce the mortality rate, we pretreated fish with cold shocks prior to shift to cold water. In this study, we show that cold-pretreated L. crocea 12days after shift to cold water increase the viability by 5.77-fold compared to the unpretreated (live fish 75 versus 13, p value = 1.775e-06, n = 100). The highest loss of 31 out of 100 fish in the unpretreated group occurred in day 3 after temperature shift. To identify the pretreatment-induced transcriptional changes that may be attributed to cold-resistance and survival, we performed RNA-seq analysis of a total of 48 fish that were prior to and 48h, 54h, and 72h after temperature shift in pretreated and unpretreated groups in sextuplicate. Transcriptomic profiling analysis indicates that pretreatment-induced transcriptional alterations of enzymes involved in FASI, β-oxidation, PUFA synthesis, oxidative phosphorylation, and molecular chaperones persisted after temperature shift, suggesting that these metabolic pathways may play a role in L. crocea cold-resistance and survival. Our study provides insights on how the pretreatment enhances the L. crocea growth fitness in cold water.

Impacts of replacement of dietary fish oil by vegetable oils on growth performance, anti-oxidative capacity, and inflammatory response in large yellow croaker Larimichthys crocea.

A 12-week feeding trial was conducted to evaluate the effects of replacement of dietary fish oil by palm and linseed oils on the growth performance, anti-oxidative capacity, and inflammatory responses of large yellow croaker (initial body weight: 36.82 ± 0.29g). The control diet was designed to contain 6.5% of fish oil, and named as FO. On the basis of the control diet, the fish oil was 100% replaced by palm and linseed oils, and these two diets were named as PO and LO, respectively. Results showed that the specific growth rate significantly reduced in the PO and LO groups. Crude lipid content in liver of fish fed FO was significantly lower than that in the PO and LO groups. Fatty acid composition in liver reflected the dietary input. Compared with the FO group, palm oil inclusion significantly decreased expressions of superoxide dismutase 1, catalase, and nuclear factor erythroid 2-related factor 2 in liver, while linseed oil inclusion significantly increased expressions of above genes. However, both of the PO and LO groups had a significantly lower total anti-oxidative capacity in liver than the fish fed FO. Dietary palm and linseed oils significantly decreased expressions of arginase I and interleukin 10, and increased expressions of tumor necrosis factor α, interleukin 1β, toll-like receptor 22, and myeloid differentiation factor 88 in liver. In conclusion, total replacement of dietary fish oil by palm and linseed oils could suppress growth performance and liver anti-oxidative capacity, and induce inflammatory responses of large yellow croaker.

Growth characteristics of cage-cultured large yellow croaker Larimichthys crocea

Large yellow croaker Larimichthys crocea (LYC) is the most cultured marine fish species in China. We described growth characteristics of cage-cultured LYC from three typical culture districts: Jiaocheng (JC), Shacheng (SC) and Xiapu (XP) in Fujian Province, China. ANOVA revealed significant differences in average body length and weight among areas (P < 0.01), with Duncan’s multiple range test indicating fishes from XP had the best grow performance. Length-weight relationships for fishes from JC, SC and XP were: W=2.39 × 10−5×L2.99, W=2.22 × 10−5×L2.96, W=1.94 × 10−5×L2.98, respectively. All groups had isometric growth, with fishes from XP having the highest asymptotic length L∞ (34.9 cm), followed by fishes from SC (33.5 cm) and JC (27.8 cm). Trends in asymptotic weight (W∞) were similar, with values for fishes from XP, SC and JC being 748.3 g, 651.0 g and 484.4 g, respectively. Inflexion points of body weight occurred at 12, 17 and 18 months of age for fishes from JC, XP and SC, respectively. A significant negative correlation was apparent between fish fatness and water temperature (r = - 0.54, P < 0.05). LYC stock had faster growth and a smaller asymptotic size within an aquaculture environment compared to wild LYC stock.

Molecular Characterization, Tissue Distribution and Localization of Larimichthys crocea Kif3a and Kif3b and Expression Analysis of Their Genes During Spermiogenesis

KIF3A and KIF3B are two N-terminal motor proteins belonging to the kinesin-II superfamily that play essential roles in spermiogenesis. To understand the roles played by KIF3A/3B during spermatogenesis of large yellow croaker Larimichthys crocea, we studied the testis characteristics at different developmental stages of L. crocea, and determined the spatiotemporal expression patterns of kif3a and kif3b during spermiogenesis. Quantitative real-time PCR (qRT-PCR) showed that the overall trends of kif3a/3b mRNA abundance during testis development are similar. From stage II to stage V, kif3a/3b mRNA abundances first increased and then fell after reaching a peak at stage IV. Interestingly, the mRNA abundances of both genes at stage V were higher than those at stages II and III. In addition, it is worth of noting that kif3b mRNA abundance was higher than that of kif3a at all stages. Fluorescence in situ hybridization results revealed that kif3a/3b mRNA abundance dynamics were consistent with the migration of mitochondria, the deformation of nucleus, and the formation of tail. The mRNA hybridization signals of both genes first appeared either around the nuclear periphery or on the side of the nuclei, then appeared at one side of nuclei, and finally were mainly on the tail during spermiogenesis. Our findings contributed to better understanding the molecular mechanisms of spermiogenesis in fish; and suggested that KIF3A and KIF3B may participate in the intracellular transport of mitochondria, nuclear deformation, and the formation of tail during the spermiogenesis in L. crocea.

Pre-hypoxia exposure inhibited copper toxicity by improving energy metabolism, antioxidant defence and mitophagy in the liver of the large yellow croaker Larimichthys crocea

This study investigated the effects of moderate hypoxia pre-exposure on energy metabolism, antioxidant defence and mitophagy in the liver of the large yellow croaker Larimichthys crocea exposed to Cu. Fish were pre-exposed to either normoxia or hypoxia (~3.0 mg L−1, 42% O2 saturation) for 48 h, and subsequently were subjected to either control (without Cu addition) or Cu (168 μg L−1) under normoxic conditions for another 48 h. Copper exposure under normoxia induced Cu toxicity that increased mortality, the production of reactive oxygen species (ROS) and malondialdehyde, and aberrant hepatic mitochondrial ultrastructure. Interestingly, hypoxia pre-exposure improved energy metabolism, antioxidant ability and mitophagy response, and reduced the Cu content to inhibit Cu toxicity, reflecting the enhanced survival rate and reduced oxidative damage. In these processes, hypoxia-inducible factor-1α (HIF-1α), transcription factors NFE2-related nuclear factor 2 (Nrf2), and forkhead box O-3 (FoxO3) mRNA levels were correlated with expression of genes related to energy metabolism, antioxidant defence and mitophagy, respectively, indicating HIF-1α, Nrf2, and FoxO3 are required for the induction of their respective target genes. Overall, moderate hypoxia pre-exposure was able to generate adaptive responses to mitigate Cu-induced toxicological effects, underlining a central role of hormesis.

Molecular cloning

Transcription factor c-Jun is a member of AP-1 transcription complex that can be induced by various pathogens and plays a broad regulatory role in vertebrate immune response. In this study, the complete c-Jun cDNA of large yellow croaker Larimichthys crocea (Lcc-Jun) was cloned, whose open reading frame (ORF) is 984 bp long and encodes a protein of 327 amino acids (aa). The deduced Lcc-Jun protein contains three highly conserved domains, a transactivation domain (TAD, Met1-His118), a DNA binding domain (DBD, Lys218-Arg243), and a Leucine zipper domain (LZD, Leu271-Leu299), as found in other specie c-Jun. Lcc-Jun was constitutively expressed in all examined tissues, with the higher levels in blood, heart, and head kidney. Its transcripts were not only induced in spleen and head kidney by poly (I: C) or LPS, but also up-regulated in primary head kidney leukocytes (PKL), macrophages (PKM), and granulocytes (PKG), suggesting that Lcc-Jun may be involved in immune responses induced by poly (I: C), a viral mimic, and LPS, a Gram-negative bacterial component. Overexpression of Lcc-Jun in PKL increased the expression of cytokines and transcription factors involved in T helper 1 (Th1: TNF-α, IFN-γ, and T-bet) and Th2 (IL-4/13 A/B, IL-6, and GATA3) cell development and differentiation, suggesting that Lcc-Jun may play a role in regulation of Th1/Th2 cell response. These results therefore led us to suggest that the c-Jun-mediated signaling pathways may have an important immune-modulatory function in teleost fish.

Impacts of ship noise on the growth and immunophysiological response in the juveniles of two Sciaenidae species,Larimichthys croceaandNibea albiflora

The wild stocks of large yellow croaker Larimichthys crocea and yellow drum Nibea albiflora have been depleted since the 1980. Although the Chinese government has put a lot of effort (e.g., implementing fishing ban and releasing artificially bred fish into naturally distributed sea areas) into restoring their natural resources, the restoration still fails to expectation. We speculate that the slow restoration may be related to the increasing ship noise near the spawning grounds of these two species of fish. To test the harmfulness of ship noise on the L. crocea and N. albiflora, in our previous study, we studied the impacts of ship noise on their behaviors, parallelly, in the present study, we focused on the impacts of noise on their immunophysiological responses. We designed two experiments. In the first experiment, the juveniles were exposed to 120 dB ship noise for only once, then the plasma physiological indices were monitored every 1 hr within 4 hr. In the second experiment, the juveniles were exposed to 120 dB noise twice a day for 30 days, afterwards, the growth, plasma immune indices and intestinal microbiota were analyzed. The results showed that stimulated by ship noise, the physiological indices of L. crocea and N. albiflora both increased sharply within 3 hr. After a month noise stimulation, the growth and immune indices decreased significantly, and the proportion of intestinal microbiota was seriously imbalanced, showing Vibrio and Pseudomonas were dominant and other genera's abundance was quite low, especially some common intestinal probiotics. In addition, we also found that N. albiflora may be more sensitive to ship noise than L. crocea in terms of the required duration of physiological indices recovering to unstimulated level, and growth. This study highlights that ship noise negatively affects L. crocea and N. albiflora, which is helpful for some departments taking measures to protect the natural resource of these two species of fish.

Bacterial diversity in gut of large yellow croaker Larimichthys crocea and black sea bream Sparus macrocephalus reared in an inshore net pen

Bacterial diversity in the foregut, midgut and hindgut of large yellow croaker Larimichthys crocea and black sea bream Sparus macrocephalus reared in an inshore net pen, formulated feed and seawater were analyzed with Illumina MiSeq high-throughput sequencing platforms. A total of 270 operational taxonomic units (OTUs) were identified from fish guts, formulated feed and seawater, which belonged to 17 phyla and 20 genera. Firmicutes and Proteobacteria dominated at the phylum level, while Bacillus, Lactococcus and Oceanobacillus dominated at the genus level, in fish gut. The similarity in bacterial community between the guts of two fish species was higher than that either between fish gut and formulated feed or between fish gut and seawater. This result indicates that bacterial communities in guts of large yellow croaker and black sea bream were independent on those in the formulated feed and seawater. The common OTUs between fish gut and formulated feed were more than that between fish gut and seawater, suggesting that the impact of the formulated feed on intestinal bacteria of large yellow croaker and black sea bream was greater relative to that of seawater in the net pen. Spatial heterogeneity in bacterial composition along the gut of large yellow croaker and black sea bream was also evaluated.

Comparative study on the organoleptic quality of wild and farmed large yellow croaker Larimichthys crocea

To fill the blank in systematic study on the organoleptic quality of large yellow croaker Larimichthys crocea, we analyzed the organoleptic quality of the fish meat of wild, trash-fish-fed, and compound-feed-fed large yellow croaker. Six fish (weight: 500 g) per group were sampled in the same period, and 89 indices of fish organoleptic quality were measured and analyzed. Results reveal significant differences in the body condition factor, skin/muscle color, flesh texture, odor, and taste aspects between wild and farmed fish. Compared with the wild fish, farmed fish showed fatter body shape, whiter skin or muscle color, tender muscle, higher level of fishy odor or volatile intensity, but lower delicious taste. In addition, compared with trash-fish feeding, compound-feed feeding could improve the body shape, skin color, flesh texture, and fish taste of large yellow croaker, but it also increased the fishy odor. In principle component analysis and cluster analysis, the present study preliminarily established the systematic evaluation with multiple indices to the quality of large yellow croaker. It shall be helpful for the evaluation or improvement of the quality of farmed large yellow croaker.

Replacement of dietary fishmeal by Antarctic krill meal on growth performance, intestinal morphology, body composition and organoleptic quality of large yellow croaker Larimichthys crocea

The present study investigated the growth performance, intestinal morphology, body composition and organoleptic quality of large yellow croaker Larimichthys crocea fed a diet containing different proportions of Antarctic krill Euphausia superba meal (0, 15, 30, 45, 60 and 75%) as a substitute for fishmeal. After a 9-week feeding trial, results showed that the specific growth rate and feed efficiency ratio were not negatively affected by dietary krill meal levels. Increasing levels of dietary krill meal linearly and quadratically increased significantly FI (P < .05). Significant positive linear trends were found between the increasing levels of dietary krill meal and carotenoid concentrations, redness (a*), yellowness (b*) in skin (P < .05). And the color can be distinguished by the human eye when 15% fishmeal protein was replaced by krill meal protein due to the total color difference (ΔE) was >3. Texture and pH in muscle were not negatively affected, however, liquid holding capacity linearly decreased (P < .05). The increasing dietary krill meal resulted in a linear decrease in most of free amino acids and a linear increase in inosinic acid (P < .05). The concentrations of EPA was linearly increased with the increasing krill meal level, n-3/n-6 ratio ranged from 0.68–0.91 within the human dietary requirements. Total amino acid profile kept unchanged among all the treatments. Although the increase of dietary krill meal significantly linearly increased the content of fluorine in muscle (P < .05), the highest content was within the safe edible limit for human. The expression levels of mTOR, 4E-BP1, eIF4E, S6K1, S6 genes related to TOR signaling pathway and phosphorylation of mTOR were not significantly changed among all treatment. These results suggested that Antarctic krill meal could be a viable alternative dietary protein source for large yellow croaker. And 6.59%–32.93% of dietary krill meal can result in a better skin color and fatty acid nutritional value in muscle without negative effects on growth performance of large yellow croaker.

Cu pre-exposure alters antioxidant defense and energy metabolism in large yellow croaker Larimichthys crocea in response to severe hypoxia

The aim of the present study was to evaluate the effects of Cu pre-exposure on antioxidant defense and energy metabolism in the liver of the large yellow croaker exposed to severe hypoxia. Fish were pre-acclimated to 0 and 30 μg Cu L−1 for 96 h, and subsequently exposed to 7.0 and 1.5 mg DO L−1 for another 24 h. Hypoxic stress alone increased reactive oxygen species and hepatic vacuoles. When compared to hypoxic stress alone, hypoxic stress plus Cu pre-exposure increased mortality and ROS production, and worsened histological structure by inhibiting antioxidant defense and aerobic metabolism, and enhancing anaerobic metabolism, suggesting Cu pre-acclimation aggravated hypoxia-induced oxidative damage. NFE2-related nuclear factor 2 and hypoxia-inducible factor-1α might participate in the transcriptional regulation of genes related to antioxidant response and energy metabolism, respectively. In conclusion, Cu pre-acclimation had a synergistic effect on antioxidant response and energy metabolism in fish under severe hypoxia, which contributes to understanding the molecular mechanisms underlying negative effects of Cu pre-acclimation against hypoxic damage in fish.

Molecular cloning and functional characterization of TRIF in large yellow croaker Larimichthys crocea

As an adaptor in Toll-like receptor (TLR) signaling pathway, Toll/interleukin-1 receptor (TIR) domain containing adaptor inducing interferon-β (TRIF) mediates downstream signaling cascades and plays important roles in host innate immune responses. In the present study, a TRIF ortholog named Lc-TRIF was identified in large yellow croaker (Larimichthys crocea). Sequence comparison analysis revealed that Lc-TRIF has a conserved TIR domain but without TRAF6 binding motif. The genome structure of Lc-TRIF is conserved, with two exons and one intron. Syntenic comparison showed that the loci of fish TRIF was different from that in mammals or birds, and TRAM was absent in the genomes of fish, amphibians, and birds, but present in mammals and reptiles. Expression analysis revealed that Lc-TRIF was broadly expressed in examined organs/tissues, with the highest expression level in gill and weakest in brain, and could be up-regulated under poly I:C, LPS, PGN, and Pseudomonas plecoglossicida stimulation. Fluorescence microscopy results showed that Lc-TRIF exhibited a global localization throughout the entire cell including the nucleus in HEK 293T cells. Additionally, luciferase assays demonstrated that Lc-TRIF expression could significantly induce NF-κB, type I IFN, IRF3 as well as IRF7 promoter activation. These results collectively indicated that Lc-TRIF was function in host antiviral and antibacterial responses via NF-κB and IRF3/7 related signaling pathway.

Rac1 GTPase is a critical factor in phagocytosis in the large yellow croaker Larimichthys crocea by interacting with tropomyosin

The Rho family GTPase Rac1 acts as a molecular switch for signal transduction to regulate various cellular functions. Here, a Rac1 homolog (LcRac1) was identified in large yellow croaker (Larimichthys crocea), one of the most economically important marine fishes. The LcRac1 protein was expressed in Escherichia coli and purified. Subsequently the specific antibody was raised using the purified fusion protein (GST-LcRac1). LcRac1 was ubiquitously expressed in all 12 tissues we examined, with the highest expression in heart and blood and the weakest expression in head-kidney and spleen. Moreover, time course analysis revealed that LcRac1 expression was obviously up-regulated in liver, spleen and head-kidney after immunization with Poly I:C, LPS and Vibrio parahemolyticus. On the other hand, on the basis of protein interaction, it was found that the LcRac1 interacted with Tropomyosin, a crucial protein in the process of phagocytosis. Furthermore, RNAi assays indicated that the phagocytic percentage and phagocytic index were significantly decreased when the LcRac1 gene was silenced by sequence-specific siRNA. Fluorescence microscopy assays revealed FITC-labeled V. parahemolyticus were remarkably decreased after LcRac1 was silenced by sequence-specific siRNA at 24 h. These findings implicate the vital role of LcRac1 in innate immunity in the large yellow croaker.

Comparative analysis of glucose metabolism responses of large yellow croaker Larimichthys crocea fed diet with fish oil and palm oil.

In order to study the effects of dietary fatty acid compositions on glucose metabolism, large yellow croaker juveniles Larimichthys crocea (initial weight, 36.80 ± 0.39g) were fed with two experiment diets for 12weeks. The two diets contained 6.5% of fish oil (FO) and palm oil (PO), respectively. Results showed that the contents of saturated fatty acids in liver and muscle, levels of glucose, triglyceride (TG), non-esterified fatty acid (NEFA), and leptin in blood were significantly higher in PO group, while the hepatic glycogen and muscle glycogen significantly decreased (P <0.05). There were no significant differences in blood insulin and adiponectin levels between the two groups (P >0.05). Compared with the FO group, the expressions of glucokinase (GK), glucose-6-phosphate dehydrogenase, glycogen synthase (GYS), glucose transporter 2 (GLUT2), insulin receptor 1 (IR1), insulin receptor substrate 1 (IRS1), insulin receptor substrate (IRS2), and protein kinase B (AKT2) were significantly decreased, and the expressions of phosphoenolpyruvate carboxykinase (PEPCK) in liver were significantly increased in the PO group. Meanwhile, the expressions of GK, phosphofructokinase, GYS, GLUT4, and insulin receptor 2 (IR2) were significantly reduced, and the expressions PEPCK, fructose-1 and 6-diphosphatase in muscle were significantly increased in the PO group. In conclusion, palm oil in diet could inhibit the utilization of glucose and promote the endogenous glucose production in large yellow croaker by reducing the sensitivity of insulin, so as to increase the blood glucose level.

Toxicological effects of waterborne Zn on the proximal and distal intestines of large yellow croaker Larimichthys crocea

The aim of the present study was to compare the differences of Zn-induced antioxidant defense, immunotoxicity and Zn homeostasis between the proximal and distal intestines of the large yellow croaker Larimichthys crocea. Fish were exposed to Zn (2 and 10 mg L-1) for 96 h. In the proximal intestine, high-concentration Zn increased mortality and oxidative damage, but reactive oxygen species (ROS), lipid peroxidation (LPO), protein carbonylation (PC) levels were not affected by low-concentration Zn, indicating Zn-induced oxidative damage was concentration-dependent. Antioxidant defense and immunotoxicity in response to Zn exposure may be involved in ROS/ NFE2-related nuclear factor 2 (Nrf2) and ROS/nuclear transcription factor κB (NF-κB) signaling pathways. In the distal intestine, Zn exposures did not induce oxidative damage, which may result from the improvement of Zn transport, antioxidant and immune defenses. Nrf2 was positively correlated with antioxidant-related gene in the distal intestine, but no relationship was observed between Nrf2 and CAT gene expressions in the proximal intestine. In conclusion, Zn induced toxicological effects were intestinal-region-dependent, which provided some novel insights into Zn toxicology.

Low temperature-induced variation in plasma biochemical indices and aquaglyceroporin gene expression in the large yellow croaker Larimichthys crocea

Low temperature influences multiple physiological processes in fish. To explore the adaptability of the large yellow croaker (Larimichthys crocea) to low temperature, the concentrations of glycerol, blood urea nitrogen (BUN), and triglycerides (TG) in plasma, as well as the expression levels of metabolism-related genes aqp7 and aqp10, were measured after exposure to low temperature stress and during subsequent rewarming. In addition, tissue samples from the intestine and liver were histologically analyzed. We found that the concentrations of plasma glycerol, BUN, and TG, decreased under low temperature stress, suggesting the metabolism of fat and protein slowed at low temperature. The expression levels of aqp7 and aqp10 mRNA were also downregulated under exposure to low temperature. Interestingly, above plasma indices and gene expression returned to basic levels within 24 h after rewarming. Furthermore, the liver and the intestine were damaged under continuous low temperature stress, whereas they were repaired upon rewarming. From the above results, we concluded that aqp7 and aqp10 genes were sensitive to low temperature, and that the decrease in their expression levels at low temperature might reduce energy consumption by L. crocea. However, the adaptation to low temperature was limited because the key metabolic tissues were damaged under continuous exposure to low temperature. Interestingly, the metabolism of L. crocea was basically back to normal within 24 h of rewarming, showing that it has high capacity of self-recovery.