Dissolved oxygen and ammonia affect ammonia production via GDH/AMPK signaling pathway and alter flesh quality in Chinese perch (Siniperca chuatsi)

The dissolved oxygen (DO) and ammonia are crucial to the growth of Chinese perch (Siniperca chuatsi). Information on the effects of DO and total ammonia nitrogen (TAN) in regulating ammonia nitrogen excretion and flesh quality in Chinese perch is scanty. This study aimed to evaluate the effects of dissolved DO at oxygen levels of 3 mg/L and 9 mg/L, as well as the TAN concentrations of 0.3 mg/L and 0.9 mg/L on ammonia excretion and flesh quality. Results showed that the ammonia contents in plasma, muscle, and liver of the 9 mg/L DO group were significantly higher than those of the 3 mg/L DO group (P < 0.05). However, the expression of AMPK-related signaling pathway genes (gdh, lkb1, and ampd) and flesh quality indicators (gumminess, chewiness, hardness) in the 9 mg/L DO group were significantly lower than those in the 3 mg/L DO group. Under long-term exposure to 0.9 mg/L TAN, the ammonia contents in plasma and gill filaments, as well as muscle flesh quality (resilience, gumminess, chewiness, cohesiveness), were significantly lower than those in the 0.3 mg/L TAN group (P < 0.05). However, the activities of GDH and AMPD enzymes in the 0.9 mg/L TAN group were significantly higher than those in the 0.3 mg/L TAN group. In summary, when fish are exposed to 3 mg/L DO and 0.9 mg/L TAN in the environment for a long time, their amino acids are used for transamination and deamination, resulting in insufficient energy supply for Chinese perch, whereas 9 mg/L DO and 0.9 mg/L TAN caused deterioration of the flesh quality.

Dietary supplementation of VA enhances growth, feed utilization, glucose and lipid metabolism, appetite, and antioxidant capacity of Chinese perch (Siniperca chuatsi)

The aim of this study was to investigate the effect of dietary vitamin A on juvenile Chinese perch (Siniperca chuatsi). Chinese perch were fed with five experimental diets containing 0, 20, 40, 60, and 80 mg VA·kg-1 for 8 weeks. Results showed that dietary vitamin A significantly influenced the fish's growth, feed utilization, glucose and lipid metabolism, appetite, and antioxidant capacity. Vitamin A-supplemented groups had higher weight gain rate (WGR) and specific growth rate (SGR) compared to the control group. Feed conversion ratio (FCR) was also lower in the vitamin A-supplemented groups. Dietary vitamin A had no significant effect on the survival rate (SR). Compared to the control group, fish fed with vitamin A had increased feed intake (FI), and the expression of appetite-promoting genes (npy and agrp) was significantly higher in the 40 mg VA·kg-1 group. Vitamin A also enhanced the utilization of dietary protein by Chinese perch. The serum glucose content of the fish fed with 40 mg VA·kg-1 diet was significantly higher than that of the control group and 20 mg VA·kg-1 diet, indicating that the promoting effect of VA on gluconeogenesis was greater than that on glycolysis. Additionally, dietary vitamin A increased the expression of lipid metabolism-related genes (hl and fas) and antioxidant genes (nrf2 and gpx) in the fish. These results suggest that the optimal vitamin A requirement of juvenile Chinese perch bream was estimated to be 37.32 mg VA·kg-1 based on broken-line regression analysis of WGR. In conclusion, this study provides valuable insights into the potential benefits of dietary vitamin A on the growth, metabolism, and antioxidant capacity of Chinese perch.

Effects of flow velocity on the growth performance, antioxidant activity, immunity and intestinal health of Chinese Perch (Siniperca chuatsi) in recirculating aquaculture systems

The cultivation of Chinese Perch (Siniperca chuatsi) in recirculating aquaculture systems (RASs) has become a common trend. To explore the effect of flow velocity on the growth performance, antioxidant activity, immunity and intestinal health of Chinese Perch in RAS, 240 Chinese Perch with an initial weight of 70.66 ± 0.34 g were selected and randomly divided into 4 groups: control group [CK, 0 body length per second (bl/s)], low flow velocity (LF, 0.4 bl/s), middle flow velocity (MF, 0.8 bl/s) and high flow velocity (HF, 1.2 bl/s) for a 56-days experiment. The results showed that the flow velocity significantly increased the weight gain rate and feed intake in Chinese Perch. At 1.2 bl/s, the flow velocity increased the intestinal trypsin content and intestinal villus length. Furthermore, the relative expression of appetite-related genes showed a tendency to increase, and the relative expression of appetite-inhibiting genes had a significant decrease in HF. Regarding immune-related indicators, the activities of alanine aminotransferase (ALT) and aspartate transaminase (AST) were significantly higher in MF and HF. However, the activities of lysozyme (LZM) significantly decreased. Moreover, the activities of total superoxide dismutase (T-SOD) and catalase (CAT) were significantly higher in the CK group than in the other groups. Excessive flow velocity also caused the mRNA level of most immune-relevant genes to markedly decrease. With regard to intestinal health, the intestinal content sequencing results showed that MF could increase the intestinal diversity index of Chinese Perch. In addition, with increasing flow velocity, the relative abundance of Proteobacteria gradually increased, while the proportion of Firmicutes decreased. In conclusion, although the high flow velocity could promote growth, feeding, and digestion, inhibit fat deposition and increase the intestinal microbial abundance, the flow velocity caused stress, which leads to a decline in immunity and increases the death rate and the risk of intestinal disease in Chinese Perch. These findings provide theoretical support for the development of RASs for Chinese Perch.

Effects of early low temperature exposure on the growth, glycolipid metabolism and growth hormone (gh) gene methylation in the late stage of Chinese perch (Siniperca chuatsi)

Temperature is an important factor affecting the early development, growth and physiology of fish, as well as on aspects of feeding and metabolism. Here, we investigated the impact of low temperature on the growth, glycolipid metabolism and growth hormone (gh) gene methylation in the late stage of Chinese perch (Siniperca chuatsi). Chinese perch larvae were exposed to temperatures with 21 °C (low temperature group (LT)) and 25 °C (control group) for 7 days, and then the LT group was slowly heated to 25 °C and raised at this temperature for two months. Results indicated that the LT group exhibited significantly lower growth rate and weight gain rate than the control group (p < 0.05), but no obvious food intake (FI) were detected yet between LT group and control group. The larvae exposed at 21 °C relative to the 25 °C group had significant decreased transcript levels of GH-IGF axis genes (gh, igf1 and igf2) in Chinese perch juvenile (p < 0.05). Further analysis of the DNA methylation levels of gh showed that the LT group had higher at the CpG sites of -3029 and - 3032 than the control group in larvae (p < 0.05), whereas the DNA methylation levels at CpG sites of -2982 and - 3039 of gh were significantly lower compared with the control group in juveniles (p < 0.05). In addition, the plasma glucose was significantly increased in the LT group (p < 0.05), suggesting the metabolism of blood glucose slowed at low temperature. In larvae, the expressions of glycolipid metabolism genes (ins-ra and ins-rb) in LT group were significantly up-regulated compared to control group in larvae (p < 0.05), while down-regulated in juveniles (p < 0.05). The expression level of ucp2 mRNA was continuously up-regulated under low temperature stress. All these data demonstrate that early exposure to low temperature affected the growth and glycolipid metabolism of Chinese perch.

Metabolic responses of Chinese perch (Siniperca chuatsi) to different levels of dietary carbohydrate

There are great differences in metabolic responses to different levels of carbohydrate among different carnivorous fish species. To explore metabolic responses of Chinese perch to moderate and high level of dietary carbohydrates, three diets containing 7.3% (LC), 17.5% (MC), and 27.5% (HC) of carbohydrates were provided to Chinese perch for 56 days. The results showed that MC and HC groups exhibited an increase in weight gain (WG) and hepatic glycogen content, and a decrease in feed conversion efficiency, compared with the LC group. The MC and HC groups also showed the increase in mRNA levels of phosphofructokinase and citrate synthase related to the aerobic oxidation pathway, which might be responsible for the increase in WG. Moreover, compared with the LC group, the HC group exhibited high levels of plasma indices (glucose, pyruvic acid, lactic acid, total triglyceride, total cholesterol, and low-density lipoprotein) and liver lipid resulting from the increased mRNA levels of fatty acid synthesis-related genes (ATP citrate lyase, acetyl-CoA carboxylase α, and fatty acid synthase), low level of crude protein caused by inhibition of TOR pathway, and liver damage induced by low antioxidant capacity and infiltration of inflammatory cells, but the MC group did not. The above results indicated that 17.5% dietary carbohydrate might be utilized effectively in Chinese perch and part carbohydrates were converted into glycogen to maintain glucose homeostasis; 27.5% dietary carbohydrate could not be fully utilized. The 27.5% carbohydrate diet induced the up-regulation of aerobic oxidation, glycogen synthesis, and fat synthesis pathways which might not be sufficient to maintain glucose homeostasis.

Genome-wide DNA methylation profiles provide insight into epigenetic regulation of red and white muscle development in Chinese perch Siniperca chuatsi

Fish skeletal muscles are composed of spatially well-separated fiber types, namely, red and white muscles with different physiological functions and metabolism. To compare the DNA methylation profiles of the two types of muscle tissues and identify potential candidate genes for the muscle growth and development under epigenetic regulation, genome-wide DNA methylation of the red and white muscle in Chinese perch Siniperca chuatsi were comparatively analyzed using bisulfate sequencing methods. An average of 0.9 billion 150-bp paired-end reads were obtained, of which 86% were uniquely mapped to the genome. Methylation mostly occurred at CG sites at a ratio of 94.43% in the red muscle and 93.16% in the white muscle. The mean methylation levels at C-sites were 5.95% in red muscle and 5.83% in white muscle, whereas the mean methylation levels of CG, CHG, and CHH were 73.23%, 0.62%, and 0.67% in red muscle, and 71.01%, 0.62%, and 0.67% in white muscle, respectively. A total of 4192 differentially methylated genes (DMGs) were identified significantly enriched in cell signaling pathways related to skeletal muscle differentiation and growth. Various muscle-related genes, including myosin gene isoforms and regulatory factors, are differentially methylated in the promoter region between the red and white muscles. Further analysis of the transcriptional expression of these genes showed that the muscle regulatory factors (myf5, myog, pax3, pax7, and twitst2) and myosin genes (myh10, myh16, myo18a, myo7a, myo9a, and myl3) were differentially expressed between the two kinds of muscles, consistent with the DNA methylation analysis results. ELISA assays confirmed that the level of 5mC in red muscle was significantly higher than in white muscle (P < 0.05). The RT-qPCR assays revealed that the expression levels of the three DNA methylation transferase (dnmt) subtypes, dnmt1, dnmt3ab, and dnmt3bb1, were significantly higher in red muscle than in white muscle. The higher DNA methylation levels in the red muscle may result from higher DNA methylation transferase expression in the red muscles. Thus, this study might provide a theoretical foundation to better understand epigenetic regulation in the growth and development of red and white muscles in animals, at least in Chinese perch fish.

The miRNA expression profile directly reflects the energy metabolic differences between slow and fast muscle with nutritional regulation of the Chinese perch (Siniperca chuatsi)

Fish skeletal muscles are composed of two distinct types, slow and fast muscles, and they play important roles in maintaining the body's movement and energy metabolism. The two types of muscle are easy to separate, so they are often used as the model system for studies on their physiological and functional characteristics. In this study, we revealed that the carbohydrate and lipid metabolic KEGG pathways are different between slow and fast muscles of Chinese perch with transcriptome analysis. In fast muscle, glucose metabolism was catabolic with higher glycolysis capacity, while in slow muscle, glucose metabolism was anabolic with more glycogen synthesis. In addition, oxidative metabolism in slow muscle was stronger than that in fast muscle. By analyzing the expression levels of 40 miRNAs involved in metabolism in the muscles of Chinese perch, 18 miRNAs were significantly upregulated and 7 were significantly downregulated in slow muscle compared with fast muscle. Based on functional enrichment analysis of their target genes, the differential expression levels of 17 miRNAs in slow and fast muscles were reflected in their carbohydrate and lipid metabolism. Among these, 15 miRNAs were associated with carbohydrate metabolism, and 6 miRNAs were associated with lipid metabolism. After 3 days of starvation, the expression levels of 15 miRNAs involved in glucose metabolism in fast and slow muscles increased. However, after 7 days of starvation, the mRNA levels of miR-22a, miR-23a, miR-133a-3p, miR-139, miR-143, miR-144, miR-181a and miR-206 decreased to basal levels. Our data suggest that the possible reason for the difference in glucose and lipid metabolism is that more miRNAs inhibit the expression of target genes in slow muscle.

Valine acts as a nutritional signal in brain to activate TORC1 and attenuate postprandial ammonia-N excretion in Chinese perch (Siniperca chuatsi)

An emerging concept is that the hypothalamic nutrient sensor can regulate peripheral energy metabolism via a brain-liver circuit. Valine is an essential branched-chain amino acid (BCAA) that drives intracellular signaling cascades by the activation of target of rapamycin complex 1 (TORC1) which is critical to protein metabolism in mammals. However, in teleost fish, it remains scarce in this area especially about how the intraventricular (ICV) injection of valine can mediate the protein metabolism in peripheral organs. This study would tentatively explore the effects of ICV injection of valine on protein metabolism in peripheral organs through evaluating the postprandial ammonia-N excretion rate in Chinese perch. The control group was injected with 5-μL PBS, and the Val group was injected with 20-μg L valine dissolved into 5-μL PBS. The ammonia-N excretion rate of Val group was lower than control group at 4-, 12-, and 24-h postinjection, while the concertation of plasma glucose was increased sharply at 0.5-, 4-, 12-, and 24-h postinjection. We further checked both mRNA level and the enzyme activity of glutamate dehydrogenase (GDH) in the liver and adenosine monophosphate deaminase (AMPD) in muscle, and we found that they were obviously decreased in Val group at 4-, 12-, and 24-h postinjection. The phosphorylation level of ribosomal protein S6, a downstream target protein of TORC1, was markedly enhanced in the liver of Val group at 4-, 12-, and 24-h postinjection. Collectively, these results illustrated that ICV injection of valine can attenuate protein degradation in peripheral organs by depressing the GDH and AMPD enzyme activity; on the other hand, the injected valine can trigger the activation of TORC1 in the liver via a brain-liver circuit and then interdict proteolysis.

MiRNAs-Modulation of Nrf2 Signaling Networks in Regulation Oxidative Stress of Chinese Perch Skeletal Muscle After Fasting Treatment

Nrf2 is an important transcription factor involved in the antioxidant response and is widely expressed in animal tissues. The function of Nrf2 is regulated by its negative regulator Keap1 by inducing its cytoplasmic degradation. Recent studies have suggested that Nrf2 is also regulated post-transcriptionally via miRNAs. However, to date, how miRNAs regulate Nrf2 in fish skeletal muscles is unknown. In this study, the full-length cDNAs with 2398 bp of the Nrf2 was firstly cloned by SMART RACE amplification tools from Chinese perch. The Nrf2 gene structure and its 3'-UTR region for possible miRNA binding sites, as well as its spatial expression profile were assayed. Then, we employed TargetScan Fish tool MiRNAnome to predict putative sites for five miRNAs including miR-181a-5p, MiR-194a, MiR-216a, miR-459-5p, and miR-724. Using qRT-PCR assay, we found that Nrf2 mRNA levels have negative correlation with all five miRNAs expression in muscle of nutritionally deprived fish, and that ectopic expression of miR-181a-5p alone reduces Nrf2 mRNA levels. Luciferase reporter assay in a heterologous cell system revealed that each of the five miRNAs reduced Nrf2 expression, suggesting a direct regulatory mechanism. Moreover, the miR-181a-5p suppression using specific antagomir led to a significant increase in Nrf2 expression in vivo. At the same time, the expression levels of the antioxidant enzymes CAT, ZnSOD, GPx, GSTA, and GSTA genes increased significantly after injecting miR-181a-5p antagomir. Taken together, these findings provide evidence that miRNAs are involved in the Nrf2 signaling networks in regulation of oxidative stress in fish, at least in Chinese perch muscle.

Impact of Aeromonas hydrophila and infectious spleen and kidney necrosis virus infections on susceptibility and host immune response in Chinese perch (Siniperca chuatsi)

Co-infections with pathogenic microorganisms are common in aquaculture, resulting in more serious economic losses than single-pathogen infection. Infection of Aeromonas hydrophila (A. hydrophila) often occurs together with infectious spleen and kidney necrosis virus (ISKNV) in Chinese perch (Siniperca chuatsi) culture ponds. In this study, A. hydrophila and ISKNV were inoculated into Chinese perch to mimic individual infection, secondary infection, and mixed infection. The effects of concurrent infections on the susceptibility and the immune response of the host and changes in bacterial and viral load were studied. The results showed relatively complex interaction between ISKNV and A. hydrophila for different infection modes, acting in an antagonistic or synergistic manner. The experimental groups infected with a mixture of ISKNV and A. hydrophila showed higher mortality rate than groups infected with single-pathogen or secondary infection groups, suggesting a synergistic lethal effect of A. hydrophila and ISKNV co-infection. Serious clinical symptoms and obvious histopathological changes were observed in moribund fish under the mixed-infection condition. In addition, obviously higher mortalities were caused by secondary bacterial infections than the number caused by secondary viral infections. ISKNV-primary infection increased the mortality caused by secondary bacterial infections, but A. hydrophila-primary infection did not significantly increase the mortality caused by secondary viral infections. Co-infected fish showed high expression levels of IRF1, Mx, Viperin, Hepcidin, TNFα, and IL-1β mRNAs relative to the levels in healthy fish, which suggested that the co-infection of these two pathogens activated the host immune system and caused host inflammation. These results of infection with A. hydrophila and ISKNV provided the theoretical basis to analyze the pathogenic effects and interaction between pathogens, and could facilitate design of strategies for clinical prevention and control measures of outbreak of fulminant hemorrhagic disease and bacterial sepsis in Chinese perch.

High-Quality Genome Assembly and Annotation of the Big-Eye Mandarin Fish (Siniperca knerii)

The big-eye mandarin fish (Siniperca knerii) is an endemic species of southern China. It belongs to the family Sinipercidae, which is closely related to the well-known North American sunfish family Centrarchidae. Determining the genome sequence of S. knerii would provide a foundation for better examining its genetic diversity and population history. A novel sequenced genome of the Sinipercidae also would help in comparative study of the Centrarchidae using Siniperca as a reference. Here, we determined the genome sequence of S. knerii using 10x Genomics technology and next-generation sequencing. Paired-end sequencing on a half lane of HiSeq X platform generated 56 Gbp of raw data. Read assembly using Supernova assembler resulted in two haplotype genomes with 732.1 Mb in size and an average GC content of 40.4%, which is consistent with genome size previously reported or estimated using k-mer counting. A total of 7,989 scaffolds with an N50 score of 12.64 Mb were obtained. The longest scaffold was 30.54 Mb. Evaluation of the genome completeness using BUSCO confirmed that 96.5% genes of the Actinopterygii Benchmarking Universal Single-Copy Orthologs were found in the assembled genome of S. knerii Gene prediction using Maker annotation kit resulted in 28,440 genes, of which 25,899 genes had at least one hit comparing to the NCBI Nr database, KEGG or InterProScan5. Pairwise sequentially Markovian coalescent (PSMC) analysis of the genome showed that there was a bottleneck event of the population of S. knerii between 70 ka - 20 ka, which was concordant with the Tali glacier period, suggesting a population decline of S. knerii probably due to climate conditions.

Growth and Metabolic Response of Chinese Perch to Different Dietary Protein-to-Energy Ratios in Artificial Diets

The effect of dietary nutrients on novel farm species has always garnered wide research and economic interest. Chinese perch, an economically important carnivorous fish, accepts an artificial diet after taming, so it is essential to evaluate and optimize the nutritional and metabolic demands of this species. However, little is known about the effect of an artificial diet on the growth and metabolism of Chinese perch. Therefore, the present study evaluated the growth and metabolic responses of Chinese perch to experimental diets with different dietary protein/energy (P/E) ratios. Five isoenergetic diets (18 kJ/g) with graded levels of P/E ratios of 30.58, 33.22, 35.90, 38.6, and 41.35 mg/kJ (named A, B, C, D, and E) were formulated. A total of 225 Chinese perch (64.89 ± 0.28 g) were divided into five groups (triplicate tanks for each group), distributed into 15 (350 L) fiberglass tanks, and fed twice a day at 4% of fish wet body weight with the respective P/E ratio diets for 10 weeks. Compared with the other groups, Chinese perch in Group C showed significantly improved growth performance, weight gain (WG), specific growth rate (SGR), viscerosomatic index (VSI), hepatosomatic index (HSI), intraperitoneal fat (IPF), feed utilization, feed intake (FI), feed conversion ratio (FCR), protein efficiency ratio (PER), protein retention efficiency (PRE), energy retention efficiency (ERE), and feed efficiency (FE) as well as whole-body, muscle, and liver composition. Chinese perch in Group A, on the other hand, had the lowest growth performance, feed utilization, and body composition compared with the other groups. The activities of nitrogen metabolism-related enzymes (alanine aminotransferase (ALT), aspartate aminotransferase (AST) glutamate dehydrogenase (GDH), and adenosine 5′-monophosphate deaminase (AMPD)) as well as the mRNA expression of the GDH and AMPD genes were significantly lower than those in the other groups. Similarly, the expression of NPY and AgRp were significantly higher in Group C compared with the other groups. However, the gene expression of CART and POMC was not affected by the dietary P/E ratios. In Group A, the expression of mTOR, S6K, and 4EBP1 was significantly lower and that of AMPK, LKB1, and eEF2 was significantly higher when compared with the other groups. Biochemical analysis of blood showed that ALT, AST, total protein (TP), alkaline phosphatase (ALP), glucose (GLU), blood urea nitrogen (BUN), and triglyceride (TG) levels were also affected by the dietary P/E ratio. From our results, we concluded that Chinese perch growth performance and nutrient metabolism were significantly affected by the P/E ratio of the artificial diet. Second-order polynomial regression analysis revealed that Chinese perch growth performance was optimal at a P/E ratio of 37.98 in the artificial diet.

Lipid deposition pattern and adaptive strategy in response to dietary fat in Chinese perch (Siniperca chuatsi)

Background

Previous studies in teleost have demonstrated the adaptive strategy to maintain hepatic lipid homeostasis within certain limit. The excess of fat-intake could induce abnormal lipid deposition in liver but not adipose tissue. However, the molecular mechanism between the impaired lipid homeostasis and the aggravated lipid deposition in liver has not been elucidated well in fish.

Methods

Four isonitrogenous diets with different fat levels (2, 7, 12 and 17%) were formulated, named L2, L7, L12 and L17 respectively, and fed Chinese perch (44.50 ± 0.25 g) to apparent satiation for five weeks. Growth index, triglyceride concentrations and expression of genes involved in lipid metabolism were measured.

Results

The maximal growth performance and food intake were observed in L12 group. The lipid content in liver and serum were comparable in L2, L7 and L12 groups, while they were increased significantly in L17 group. Histology analysis also demonstrated that mass lipid droplets emerged in hepatocyte and then induced hepatic steatosis in L17 group. Compared to L2 group, the lipolytic genes related to fatty acids (FAs) transport (lpl & hl) and FAs β-oxidation (cpt1 & cs) were increased in L7 and L12 group. Relative mRNA levels of the gluconeogenesis (pc, pepck & g6pase) were also increased, in contrast, the lipogenic genes (srebp1, accα & fas) were decreased. Compared to L12 group, L17 group had higher mRNA levels of the FAs transport and the lipogenesis. But the lipolytic genes related to FAs β-oxidation were steady and the mRNA levels of gluconeogenesis were down-regulated instead.

Conclusions

Within certain limit, the increase of dietary fat in L7 and L12 group was propitious to reduce the consumption of protein and improve growth performance in Chinese perch. It was due to the homeostasis of hepatic triglyceride (TG) pool and serum glucose through promoting the FAs β-oxidation and gluconeogenesis respectively. Both the increase of lipogenesis and the absence of FAs β-oxidation in L17 group could trigger the esterification of FAs, indeed, the inhibition of gluconeogenesis could also aggravate triglyceride accumulation in liver and induce hepatic steatosis.

An avirulent Micropterus salmoides rhabdovirus vaccine candidate protects Chinese perch against rhabdovirus infection

In order to develop live vaccine against Siniperca chuatsi rhabdovirus (SCRV) disease, an avirulent virus strain, designed as Micropterus salmoides rhabdovirus Sanshui (MSRV-SS), was selected from six fish rhabdovirus isolates (SCRV-QY、SCRV-SS、SCRV-GM、CMRV-FS、OMBRV-JM、MSRV-SS) by fish challenge assay. When Chinese perch (Siniperca chuatsi) were intraperitoneally injected live virus strain MSRV-SS, they were completely protected from virulent SCRV-GM challenge with a relative percent survival (RPS) of 100% on 18th day post vaccination. Then, the wild type MSRV-SS was purified by plaque clone assays, and the biological characteristics of the clonal strain designed as MSRV-SS-7 were investigated. The MSRV-SS-7 was avirulent to Chinese perch and its growth characteristic was similar to the MSRV-SS. The immune protection effects of clonal MSRV-SS-7 against virulent SCRV-GM were evaluated by intraperitoneal injection (IP) vaccination and immersion (IM) vaccination, their RPSs were all 100%. Altogether, these results indicate that MSRV-SS-7 is a potential live vaccine candidate against SCRV disease.

Co-infections of infectious spleen and kidney necrosis virus and Siniperca chuatsi rhabdovirus in Chinese perch (Siniperca chuatsi)

In spite of the quite common co-infections of viruses in the cultured fish, most of the previous studies have just simply focused on the infection of a single pathogen. In this report, we observed that about 13% of cultured Chinese perch have been co-infected by infectious spleen and kidney necrosis virus (ISKNV) and Siniperca chuatsi rhabdovirus (SCRV). Furthermore, Chinese perch could co-infected by ISKNV and SCRV by intraperitoneally injection with the two viruses. Interestingly, we revealed that the two viruses could even co-infect a single cell of Chinese perch in vivo and a single Chinese perch brain cells (CPB) cell in vitro. The dynamic co-infected viruses loads in the different tissues of Chinese perch showed dependent. When CPB cells were infected with the same 10 MOI of SCRV and ISKNV, the replication of SCRV overwhelmed the replication of ISKNV. When the MOI of ISKNV (10 MOI) was 10,000 times of MOI of SCRV (0.001 MOI), the dynamic virus loads of the two viruses in CPB cells indicated that co-infections could synergistically stimulate both viruses replication at the late time points but not at early time points. The co-infections of ISKNV and SCRV in the cultured Chinese perch will shed a new light on the prevention of the viral diseases of Chinese perch. The development of multivalent vaccine which could be effective for preventing against the co-infections of the viruses is highly needed.

Identification and profiling of growth-related microRNAs in Chinese perch (Siniperca chuatsi)

Background

MicroRNAs (miRNAs) are endogenous small non-coding RNAs that play important roles in the regulation of diverse biological processes in eukaryotes. Chinese perch (Siniperca chuatsi) is one of the most economically important fish species widely cultured in China. Growth is an extremely important characteristic in fish. Individual differences in body size are common in Siniperca chuatsi, which significantly influence the aquaculture production of Siniperca chuatsi. However, the underline growth-related regulatory factors, such as miRNAs, are still unknown.

Results

To investigate the growth-related miRNAs in Siniperca chuatsi, two RNA libraries from four growth-related tissues (brain, pituitary, liver, and muscle) of Siniperca chuatsi at 6-month stage with relatively high or low growth rates (big-size group or small-size group) were obtained and sequenced using Solexa sequencing. A total of 252 known miRNAs and 12 novel miRNAs were identified. The expression patterns of these miRNAs in big-size group and small-size group were compared, and the results showed that 31 known and 5 novel miRNAs were differently expressed (DE). Furthermore, to verify the Solexa sequencing, five DE miRNAs were randomly selected and quantified by quantitative reverse transcription polymerase chain reaction (qRT-PCR). The results showed that their expression patterns were consistent with those of Solexa sequencing. In addition, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis of target genes of DE miRNAs was performed. It showed that the target genes were involved in multiple biological processes including metabolic process, suggesting that metabolic process played an important role in growth of fish.

Conclusions

Siniperca chuatsi is a popular and economically important species in aquaculture. In this study, miRNAs in Siniperca chuatsi with different growth rates were identified, and their expression profiles were compared. The data provides the first large-scale miRNA profiles related to growth of Siniperca chuatsi, which is expected to contribute to a better understanding of the role of miRNAs in regulating the biological processes of growth and possibly useful for Siniperca chuatsi breeding.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-3851-y) contains supplementary material, which is available to authorized users.

Effects of fasting, temperature, and photoperiod on preproghrelin mRNA expression in Chinese perch

Preproghrelin, a gut/brain peptide, plays an important role in the regulation of food intake and energy homeostasis in teleost and mammals. In the present study, we obtained the full-length preproghrelin cDNA in Chinese perch. The preproghrelin messenger RNA (mRNA) tissue expression showed that level was much higher in stomach and pituitary than in other tissues. The fasting study showed, after gastric emptying (3-6 h), short-term fasting (6-12 h) increased preproghrelin expression in the stomach. While in the pituitary, fasting reduced preproghrelin expression at 1, 3, 12, and 48 h, presenting state fluctuation of self-adjustment. The temperature study showed that the mRNA expression of preproghrelin was the highest in the brain at 26 °C and highest in the stomach at 32 °C, respectively, with different optimum temperature in these two tissues, reflecting spatiotemporal differences of regulation by central nervous system and peripheral organs. The photoperiod study showed that normal light (11 h of lightness and 13 h of darkness) led to highest preproghrelin expression, both in the brain and in the stomach, than continuous light or continuous dark, proving food intake is adapted to natural photoperiod or normal light in this study. These results all indicated that tissue-specific preproghrelin expression of Chinese perch could be significantly affected by environmental factors. Short-term fasting of 6 h after gastric emptying, 26 °C, and normal light led to higher preproghrelin expression, which indicated potential appetite increase in Chinese perch.

Application and development of a TaqMan real-time PCR for detecting infectious spleen and kidney necrosis virus in Siniperca chuatsi

Infectious spleen and kidney necrosis virus (ISKNV) is one of the major epidemiological agents that had caused great economic loss in Chinese perch (Siniperca chuatsi). In this study, a specific TaqMan real-time PCR was developed using a pair of primers and a TaqMan probe specific to the ORF007 gene of ISKNV to rapidly detect ISKNV copies in Chinese perch samples. This assay was optimized to produce linearity from 8.75 × 10⁸ to 8.75 × 10¹ copies in standard curve with an efficiency of 98% and a R² value of 0.9999. Moreover, the minimum detection limit of this assay was 10,000 times more sensitive than that of conventional PCR method. The coefficients of variation of intra- and inter-assay repeatability were less than 2.4% and 3.3%, respectively. The viral distribution in different tissues of diseased Chinese perch was evaluated by TaqMan real-time PCR method and the highest level of viral copies was detected in spleen. Among the 76 diseased Chinese perch clinical samples, 35 and 29 were positive samples based on the TaqMan real-time PCR and conventional PCR methods, respectively, indicating that the TaqMan real-time PCR was more sensitive than conventional PCR. Therefore, the TaqMan real-time PCR should be a useful tool for the early surveillance and quantitation of ISKNV.

Daily rhythmicity of clock gene transcript levels in fast and slow muscle fibers from Chinese perch (Siniperca chuatsi)

Background

Clock genes are considered to be the molecular core of biological clock in vertebrates and they are directly involved in the regulation of daily rhythms in vertebrate tissues such as skeletal muscles. Fish myotomes are composed of anatomically segregated fast and slow muscle fibers that possess different metabolic and contractile properties. To date, there is no report on the characterization of the circadian clock system components of slow muscles in fish.

Results

In the present study, the molecular clock components (clock, arntl1/2, cry1/2/3, cry-dash, npas2, nr1d1/2, per1/2/3, rorα and tim genes) and their daily transcription levels were characterized in slow and fast muscles of Chinese perch (Siniperca chuatsi). Among the 15 clock genes, nrld2 and per3 had no daily rhythmicity in slow muscles, and cry2/3 and tim displayed no daily rhythmicity in fast muscles of the adult fish. In the slow muscles, the highest expression of the most clock paralogs occurred at the dark period except arntl1, nr1d1, nr1d2 and tim. With the exception of nr1d2 and tim, the other clock genes had an acrophase at the light period in fast muscles. The circadian expression of the myogenic regulatory factors (mrf4 and myf5), mstn and pnca showed either a positive or a negative correlation with the transcription pattern of the clock genes in both types of muscles.

Conclusions

It was the first report to unravel the molecular clock components of the slow and fast muscles in vertebrates. The expressional pattern differences of the clock genes between the two types of muscle fibers suggest that the clock system may play key roles on muscle type-specific tissue maintenance and function.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-3373-z) contains supplementary material, which is available to authorized users.