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Rainbow trout (Oncorhynchus mykiss) is a significant cold-water fish farmed in China. Currently, most molecular marker-assisted breeding applications in rainbow trout rely on SSR markers. Although many rainbow trout SSR markers have been developed, methods for mining many polymorphic SSR markers from the genome and identifying them efficiently and rapidly are still lacking. For this reason, this study used in silico simulation method to rapidly develop a large number of polymorphic SSR markers quickly. A total of 354,613 SSR loci with two to six nucleotide repeat motifs were mined from 32 chromosomes of the rainbow trout reference genome using GMATA. The chromosome sequences of the reference genome were then aligned to the whole genome sequencing data (10×) of 68 rainbow trout samples. In silico genotyping was performed using the HipSTR programme to compare and count the variation in the number of repeats of the motifs of the SSR loci in the samples. The loci with high deletion rates and monomorphism were discarded, while those with more than one nonreference allele were kept. The final set of polymorphic SSR loci screened was 78,828. Finally, 4,821 SSR loci were selected with more than 3 alleles and no deletion in all rainbow trout samples and were physically mapped. The average polymorphic information content of these loci was 0.692, indicating high levels of polymorphism. These SSRs were utilized to analyse the genetic diversity and population structure of the 68 rainbow trout samples. The results showed that these 68 samples were divided into two groups. These newly discovered polymorphic SSR markers will provide valuable information for evaluating the construction of rainbow trout family lines for genetic diversity and improvement. [ABSTRACT FROM AUTHOR]

Being the world's largest seafood producer, China's mariculture is critical for ensuring national and global food security, yet greatly threatened by climate change. It is essential to assess the potential opportunities and challenges for Chinese mariculture in light of climate change. Although the impact of climate change on mariculture potential at a global scale has been investigated, studies at sub-national scales of China are scarce, particularly those that take into account multiple environmental stressors and species. Here, we applied a combination of physical and biological models to quantify the spatiotemporal variation in the mariculture potential of seven finfish species and seven bivalve species cultured in China under the emission scenarios SSP5-8.5 and SSP1-2.6 in the twentyfirst century. Our results demonstrated that the spatiotemporal trends in culture potential was species-specific. Finfish was less affected than bivalves. Four finfish species and seven bivalve species showed a continuously declining trend in culture potential and most species showed a northward shift of the centroid with high growth potential under SSP5-8.5. Under the scenario SSP1-2.6, the culture potential of finfish species mostly showed a stable or increasing trend, while that of bivalve species declined in the mid-twentyfirst century and partially recovered in the late twentyfirst century. Cold-water species exhibited a greater loss of culture potential than warm-water and eurythermal species. In the SSP5-8.5 and SSP1-2.6 scenarios, the cold-water species Oncorhynchus mykiss and Patinopecten yessoensis experienced the most significant loss in culture potential among finfish and bivalve species. Meanwhile, the culture potential for two out of the four warm-water species, specifically Epinephelus spp. and Sciaenops ocellatus, saw an increase. The culture potential for eight eurythermal species remained stable or declined. This study helps to identify mariculture potential for different species and sea areas and can inform the development of climate-resilient mariculture in China. [ABSTRACT FROM AUTHOR]

Simple Summary: Doxycycline, an approved aquacultural antibiotic, is extensively used in the treatment of bacterial diseases in fish. Since fish are poikilothermic organisms, their body temperature and metabolic rate are primarily influenced by the temperature of the water. Therefore, temperature may be affected by pharmacokinetic behavior and withdrawal times of drugs. The current study was undertaken to look at the differences in pharmacokinetics, tissue residues, and withdrawal times of doxycycline following oral administration in rainbow trout reared at 10 and 17 °C. The increment of water temperature from 10 to 17 °C decreased the elimination half-life, the body clearance, and the distribution volume of doxycycline and increased plasma concentrations. The withdrawal times for plasma and tissues decreased with the temperature increase. The results contributed to the determination of an optimal dosing regimen and the safe consumption of edible tissues in rainbow trout that were administered doxycycline and reared at different temperatures. The purpose of this study was to compare the pharmacokinetics, tissue residues, and withdrawal times of doxycycline after oral administration in rainbow trout reared at 10 and 17 °C. Fish received a 20 mg/kg oral dose of doxycycline after a single or 5-day administration. Six rainbow trout were used at each sampling time point for plasma and tissue samples, including liver, kidney, and muscle and skin. The doxycycline concentration in the samples was determined using high-performance liquid chromatography with ultraviolet detector. The pharmacokinetic data were evaluated by non-compartmental kinetic analysis. The WT 1.4 software program was used to estimate the withdrawal times. The increase of temperature from 10 to 17 °C shortened the elimination half-life from 41.72 to 28.87 h, increased the area under the concentration–time curve from 173.23 to 240.96 h * μg/mL, and increased the peak plasma concentration from 3.48 to 5.50 μg/mL. At 10 and 17 °C, the doxycycline concentration was obtained in liver > kidney > plasma > muscle and skin. According to the MRL values stated for muscle and skin in Europe and China (100 μg/kg) and in Japan (50 μg/kg), the withdrawal times of doxycycline at 10 and 17 °C were 35 and 31 days, respectively, for Europe and China and 43 and 35 days, respectively, for Japan. Since temperature significantly affected pharmacokinetic behavior and withdrawal times of doxycycline in rainbow trout, temperature-dependent dosing regimens and withdrawal times of doxycycline might be necessary. [ABSTRACT FROM AUTHOR]

Fluoranthene (FLU) has gained much attention in recent years because of its continuous discharge in natural waters and toxicity to aquatic ecosystems. However, it is difficult to control and manage FLU pollution because of the lack of a rational and scientific water quality criteria (WQC) of FLU. To solve these data gaps, the US EPA established an interspecies correlation estimation (ICE) model, which can be utilized to develop the SSD and HC5 (hazardous concentration, 5th percentile). Moreover, an improved model was developed using a combination of North American ICE models supplemented with China-specific species. In this study, to verify the applicability of the two ICE models, measured acute toxicity data for FLU were obtained from 9 acute toxicity tests using indigenous Chinese aquatic species from different taxonomic levels. Original and improved ICE-based SSD curves, which were generated using 3 surrogate species (Daphnia magna, Oncorhynchus mykiss, and Lepomis macrochirus), were compared with SSD curves based on measured data. The results showed that HC5 was 1.838, 1.062, and 0.570 mg/L for the original ICE, improved ICE, and measured data, respectively. The improved ICE-based HC5 value for FLU was within twofold of the HC5 value based on measure data, while the original ICE-based HC5 value was threefold higher than the HC5 value based on measure data. This indicated that the improved ICE had better predictability in extrapolating data with acceptable deviation than the original ICE. Furthermore, their differences between HC5 derived from two SSD curves were not significant. Generally, the improved ICE model was verified as a valid approach for generating SSDs with limited toxicity data and for deriving WQC for FLU. [ABSTRACT FROM AUTHOR]

Infectious pancreatic necrosis virus (IPNV) is the causative agent of rainbow trout (Oncorhynchus mykiss) IPN and causes significant loss of fingerlings. The currently prevalent IPNV genogroups in China are genogroups 1 and 5. However, in this study, we isolated and identified a novel IPNV, IPNV-P202019, which belonged to genogroup 7. Here, a total of 200 specific-pathogen-free rainbow trout (10 g average weight) were divided randomly into four groups to investigate the distribution of different IPNV strains (genogroups 1, 5, and 7) in 9 tissues of rainbow trout by means of intraperitoneal (ip) injection. Fish in each group were monitored after 3-, 7-, 14-, 21- and 28- days post-infection (dpi). The study showed no mortality in all groups. The distribution of IPNV genogroups 1 and 5 was similar in different tissues and had a higher number of viral loads after 3, 7, or 14 dpi. However, the distribution of IPNV genogroup 7 was detected particularly in the spleen, head kidney, and feces and had a lower number of viral loads. The results of this study provide valid data for the distribution of IPNV in rainbow trout tissues and showed that IPNV genogroups 1 and 5 were still the prevalent genogroups of IPNV in China. Although rainbow trout carried IPNV genogroup 7, the viral load was too low to be pathogenic. [ABSTRACT FROM AUTHOR]

Infectious hematopoietic necrosis virus (IHNV) is a major fish viral pathogen causing acute clinical disease and death in a variety of salmonids. IHNV isolates have been classified into five major genogroups according to the phylogenetic analysis of partial G gene fragments or the complete G gene sequence: U, M, E, L and J. Genogroup U strains have been reported in North America and Japan prior to 1982, and genogroup J is the only genogroup that has been reported in China. Here, one of IHNV strain (BjLL) was isolated from a local farm in China and were characterized in this study. The homogenate tissues of infected fry induced IHNV‐positive cytopathic effects in epithelioma papulosum cyprinid (EPC) cells that were confirmed by RT‐PCR and sequencing. The complete genome sequence of BjLL comprised 11,129 nucleotides, which had been submitted to GenBank (accession no. MF509592). By the sequence comparison and phylogenetic analysis for the G gene sequence of BjLL with 51 reference sequences in GenBank, we confirmed that this Chinese isolate belonged to genogroup U. Furthermore, virus exposure experiments with juvenile rainbow trout were conducted to assess the virulence and pathogenicity of BjLL. Compared with GS‐2014 of genogroup J, BjLL was an obviously less virulent strain that could result in lower mortality. Besides, typical clinical symptoms and pathological damages could be seen in fish following infection of BjLL. The present study is the first report of genogroup U IHNV infection in China and will provide essential information for future studies on pathogenesis of IHNV BjLL and development of efficient control strategies. [ABSTRACT FROM AUTHOR]

The reduction of the fish and non-fish resources in the World Ocean (in particular in the Black Sea) over the last 20 - 30 years is an indisputable fact. This is due to many factors, but anthropogenic ones are dominant. Among them the most important are overfishing of hydrobionts, poor water quality and climate change. A real alternative to compensate these losses and to creat healthy sources of quality seafood for humans is aquaculture - technology that can satisfy the "protein" hunger worldwide. In this regard, the purpose of the present article is to analyze the state of the Bulgarian Black Sea aquaculture and to outline the prospects for its development, based on native and introduced marine species. Modern aquaculture production in Bulgaria is dominated by the production cyprinids and salmonids in freshwater aquaculture farms, and by black mussel (Mytilus galloprovincialis) only in marine aquaculture farms. This imbalance (81.7% vs 18.3%) shows that the resources of the Bulgarian Black Sea water areas are not used sufficiently for this purpose. The indepth analysis of available literature sources (scientific articles, official reports, monographs, plans and programs, etc.), as well as the shared experience of colleagues from China, the world leader in the field of fish farming and aquaculture, give us grounds to consider the following species as promising for cultivation in the Bulgarian Black Sea water areas: Rainbow trout (Oncorhynchus mykiss Walbaum, 1792), Mullet (Mugil cephalus Linnaeus, 1758), Turbot (Psetta maxima Linnaeus, 1758), White mussel (species of bivalve molluscs: Chamelea galina Linnaeus, 1758, Donax trunculus Linnaeus, 1758, Mya arenaria Linnaeus, 1758 and Anadara kagoshimensis Tokunaga, 1906), Rapana (Rapana venosa Valenciennes, 1846), shrimp, micro- and macro- algae, introduced marine species like Sea cucumber (Holothuroidea). Future studies will show which species are environmentally friendly and cost-effective for cultivation in Bulgarian Black Sea aquatory. [ABSTRACT FROM AUTHOR]

BACKGROUND Financial loss and health risk caused by the substitution of rainbow trout for other salmonid species have become a common issue around the world. The situation could be further exacerbated in China by the 'abused' common name of San Wen Yu (the corresponding Chinese ideogram 三文鱼) for salmonids, considering the absence of a standardized naming system for seafood species. To prevent such episodes, the present study aimed to develop novel loop‐mediated isothermal amplification (LAMP) and polymerase chain reaction (PCR) assays targeting the mitochondrial cytochrome b gene for rapid identification of rainbow trout in processed fish products. RESULTS: Rainbow trout‐specific primers (LAMP and PCR) were designed, and the specificity against 23 different fish species was confirmed. The minimum amount of detectable DNA for LAMP assay reached 500 pg, up to 10‐fold less than for PCR assay. In addition to agarose gel electrophoresis, naked‐eye inspection of the LAMP‐positive samples using SYBR Green I under daylight or ultraviolet light was also validated. Finally, commercial San Wen Yu products made from rainbow trout could be accurately identified using the newly developed LAMP and PCR assays, further cross‐confirmed by mini DNA barcoding and neighbor‐joining dendrograms. CONCLUSIONS: The LAMP and PCR assays established in the study allow a fast and accurate identification of rainbow trout in processed fish products. © 2020 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

In order to meet the demand of salmon market, Chinese scientists and entrepreneurs are working on salmon mariculture far offshore in the Yellow Sea, China. Rainbow, steelhead trout and Atlantic salmon were selected as the main culture species. The aims of the present study were as follows: (a) investigate the effect of the salinity acclimation method on the growth, osmoregulation and energy budget in two forms of Oncorhynchus mykiss, rainbow and steelhead trout and (b) explore the optimal size of steelhead trout for the seawater entry. In trial I, rainbow (mean = 99.44 g) and steelhead trout (mean = 99.01 g) were reared for 40 days after undergoing salinity acclimation at three rates: an abrupt increase in salinity from 0 to 30 g/L (T30); an abrupt increase in salinity to 14 g/L, followed by a daily increase of 2 g/L (T2) or 6 g/L (T6) until reaching 30 g/L; and no salinity exposure (control treatment) (T0). In trial II, steelhead trout with body weights of approximately 100 and 400 g were cultured for 60 days with two treatments, T0 and T2, and the specific growth rate (SGR) was calculated every 10 days. In trial I, in both kinds of fish, the optimal growth performance, survival rate, osmoregulation and energy budget were observed in the T0 treatment, followed by the T2 treatment. These results indicate that O. mykiss with a body weight of approximately 100 g can adapt to sea water with a gradual transition (T2), but they are still not suitable for the seawater entry because of low growth. Based on the recorded SGRs in trial II, our formulated regression formula revealed that approximately 200 g is the optimal size of steelhead trout for the transition to sea water. [ABSTRACT FROM AUTHOR]

Specific locus amplified fragment sequencing‐based genotyping was performed in rainbow trout, Oncorhynchus mykiss with 385 individuals from a freshwater breeding program in China to develop genome‐wide single nucleotide polymorphism markers. Genomic prediction and variance component estimation were carried out for carcass fat content using genomic‐relatedness‐based best linear unbiased predictor (GBLUP) and genomic‐relatedness‐based restricted maximum likelihood methods. The 10‐fold cross‐validation analysis results showed that the genetic model including both additive and dominance effects had the best accuracy, and the observed predictive ability of the GBLUP estimates was 0.455 ± 0.050. Using this model to analyze the full data set of 385 individuals, the additive genomic heritability of carcass fat content was hα2 = 0.623 ± 0.175 with a negligible dominance effect. Our results suggested that the carcass fat content was mainly controlled by additive alleles. Thus, selective breeding could be performed based on the additive GBLUP values, and the methodology of genomic selection provides a reliable and feasible approach for optimizing carcass fat content of rainbow trout. [ABSTRACT FROM AUTHOR]

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• A recombinant IHNV virus expressing VP2 gene of IPNV was successfully constructed. • The recombinant virus showed significant protection efficacy against IHNV and IPNV. • The recombinant virus induced upregulation of innate and adaptive immune responses. • The recombinant virus could be a vaccine candidate protecting rainbow trout against two or more diseases. Infectious pancreatic necrosis virus (IPNV) and infectious hematopoietic necrosis virus (IHNV) are two common viral pathogens that cause severe economic losses in all salmonid species in culture, but especially in rainbow trout. Although vaccines against both diseases have been commercialized in some countries, no such vaccines are available for them in China. In this study, a recombinant virus was constructed using the IHNV U genogroup Blk94 virus as a backbone vector to express the antigenic gene, VP2, from IPNV via the reverse genetics system. The resulting recombinant virus (rBlk94-VP2) showed stable biological characteristics as confirmed by virus growth kinetic analyses, pathogenicity analyses, indirect immunofluorescence assays and western blotting. Rainbow trout were immunized with rBlk94-VP2 and then challenged with the IPNV ChRtm213 strain and the IHNV Sn1203 strain on day 45 post-vaccination. A significantly higher survival rate against IHNV was obtained in the rBlk94-VP2 group on day 45 post-vaccination (86%) compared with the PBS mock immunized group (2%). Additionally, IPNV loads decreased significantly in the rBlk94-VP2 immunized group in the liver (28.6-fold to 36.5-fold), anterior kidney (21.7-fold to 44.2-fold), and spleen (14.9-fold to 22.7-fold), as compared with the PBS mock control group. The mRNA transcripts for several innate and adaptive immune-related proteins (IFN-γ, IFN-1, Mx-1, CD4, CD8, IgM, and IgT) were also significantly upregulated after rBlk94-VP2 vaccination, and neutralizing antibodies against both IHNV and IPNV were induced on day 45 post-vaccination. Collectively, our results suggest that this recombinant virus could be developed as a vaccine vector to protect rainbow trout against two or more diseases, and our approach lays the foundations for developing live vaccines for rainbow trout. [ABSTRACT FROM AUTHOR]

Rainbow trout is one of the fastest-growing aquaculture species and infectious hematopoietic necrosis virus (IHNV) is endemic throughout almost all rainbow trout farms in China nowadays. In this study, IHNV GS21 was identified as the causative pathogen, which resulted in massive mortality of rainbow trout occurring in northwest China. GS21 isolate was propagated in Chinook salmon embryonic cell line (CHSE-214) and induced apparent cytopathic effects (CPE) at 3 days post-infection (dpi). Phylogenetic analysis revealed that GS21 isolate was clustered with other reported Chinese isolates within the J genogroup. Moreover, the complete cDNA sequence of GS21 isolate was obtained and it possesses more than 98 % of ANI values and 89 % of DDH values with other Chinese IHNV isolates. The detailed sequence analysis of G gene revealed the distinct amino acid substitutions of G230, G252, G270, and I277 in GS21 isolate. Furthermore, the artificially infected rainbow trout exhibited similar clinical disease symptoms as natural infection did. The cumulative mortality infected by GS21 isolate of 104 PFU/mL reached 93 % at approximately 13.5 °C. Additionally, viral loads in tissues increased first and declined then as well as the expression of immune-associated genes. Collectively, our results characterized a novel IHNV GS21 isolate that can lead to massive mortality in juvenile rainbow trout and provided a basis to define the pathogenic characteristics and evolutionary relationship of IHNV and host immune response against IHNV infection. • IHNV GS21 is identified as the causative pathogen of the emerging rainbow trout disease in Gansu nowadays. • GS21 possesses distinct substitutions of G230, G252, G270, and I277 in G protein compared to other reported IHNV isolates. [ABSTRACT FROM AUTHOR]

Rainbow trout (Oncorhynchus mykiss) is an important cold-water fish widely cultivated in China. The frequent occurrence of viral diseases caused by infectious hematopoietic necrosis virus (IHNV) seriously restricted the healthy development of the rainbow trout farming industry. However, the immune defense mechanism induced by IHNV in rainbow trout has not been fully elucidated. In the present study, we detected mRNA and miRNA expression profiles in rainbow trout head kidney after IHNV infection using RNA-seq and identified key immune-related genes and miRNAs. The results showed that a total of 7486 genes and 277 miRNAs were differentially expressed, and numerous differentially expressed genes (DEGs) enriched in the immune-related pathways such as Toll-like receptor signaling pathway, RIG-I-like receptor signaling pathway, NOD-like receptor signaling pathway, cytokine-cytokine receptor interaction, and JAK-STAT signaling pathway were significantly up-regulated, including LGP2 , MDA5 , TRIM25 , IRF3 , IRF7 , TLR3 , TLR7 , TLR8 , MYD88 , and IFN1. Integration analysis identified six miRNAs (miR-141-y, miR-200-y, miR-144-y, miR-2188-y, miR-725-y, and miR-203-y) that target at least six key immune-related genes (TRIM25 , LGP2 , TLR3 , TLR7 , IRF3 , and IRF7). Further, we verified selected immune-related mRNAs and miRNAs through qRT-PCR and confirmed the reliability of the RNA-seq results. These findings improve our understanding of the immune mechanism of rainbow trout infected with IHNV and provide basic data for future breeding for disease resistance in rainbow trout. • A total of 7486 genes and 277 miRNAs were differentially expressed in rainbow trout head kidney following IHNV infection. • Numerous differentially expressed genes enriched in the immune-related signaling pathways were significantly up-regulated. • Integration analysis identified six miRNAs that target at least six key immune-related genes. [ABSTRACT FROM AUTHOR]

Infectious pancreatic necrosis virus (IPNV) is the pathogen of infectious pancreatic necrosis (IPN), which can cause high mortality in salmonids, harm the healthy development of salmon-trout aquaculture, and lead to huge economic losses. However, in China, there is currently neither a commercially available vaccine to prevent IPNV infection nor antiviral drugs to treat IPNV infection. The genome of IPNV consists of two segments of dsRNA named A and B. Segment B encodes the RNA-dependent RNA-polymerase (RdRp) VP1 which is essential for viral RNA replication and is therefore considered an important target for the development of antiviral drugs. In this study, we investigate whether 2′-C-methylcytidine (2CMC), a nucleoside analog which target viral polymerases, has an inhibitory effect on IPNV both in vitro and in vivo. The results show that 2CMC inhibits IPNV infection by inhibiting viral RNA replication rather than viral internalization or attachment. In vivo experiment results showed that 2CMC could inhibit viral RNA replication and reduce viral load in rainbow trout (Oncorhynchus mykiss). In our study, we have revealed that 2CMC has a potent inhibitory effect against IPNV infection. Our data suggest that 2CMC is an attractive anti-IPNV drug candidate which will be highly valuable for the development of potential therapeutics for IPNV. • 2CMC inhibits IPNV infection both in vitro and in vivo. • 2CMC inhibits viral replication rather than viral internalization and attachment. • The antiviral effect of 2CMC was via inhibiting RdRp. • 2CMC may be a promising drug for treating IPNV infections. [ABSTRACT FROM AUTHOR]

Infectious pancreatic necrosis virus (IPNV) is the causative pathogen of infectious pancreatic necrosis (IPN), which causes high mortality and great economic losses in salmon and trout aquaculture. IPNVs are divided into seven genotypes, and all IPNV isolates that have been reported in China belong to genogroups I and V. Because of restrictions on imported vaccines, China has no commercial vaccine against IPNV; Therefore, more effective antiviral drugs and vaccines are needed. Traditional Chinese medicine (TCM) has been used to treat endemic and pandemic diseases and is reported effective against viral infections. We screened a TCM library containing 1483 compounds and found that bufalin exhibited anti-IPNV activity. Bufalin inhibits infections from IPNV genogroups I and V by inhibiting viral internalization and RNA replication rather than viral attachment. In vivo results showed that bufalin significantly inhibited viral loads in IPNV-targeted tissues in rainbow trout. Mechanistic research showed that bufalin's antiviral effects occurred via Na+/K+-ATPase. Our results indicate that bufalin inhibits IPNV infections both in vitro and in vivo and may be a promising drug for treating IPNV infections. • Bufalin inhibits IPNV infection both in vitro and in vivo. • Bufalin inhibits viral internalization and RNA replication rather than viral attachment. • The antiviral effect of bufalin was via Na+/K+-ATPase. • Bufalin may be a promising drug for treating IPNV infections. [ABSTRACT FROM AUTHOR]

Organochlorine pesticides (OCPs) and organophosphate pesticides (OPPs) posed severe threats to the aquatic environment in China. The toxicity data of 18 priority OCPs and OPPs for Chinese and American species were collected, and their species sensitivity distributions (SSDs) and ecotoxicity were compared. Physicochemical characteristics and chemical structures were used to analyze the difference in the pesticide toxicity. Results suggested that there is no significant difference between the HC 5 values (hazardous concentration protecting 95% of species) of China and America as a whole. However, the HC 5 values of nearly half of these pesticides (8/18) differ dramatically between Chinese and American due to the different resident species distribution. It indicated that it is necessary to develop local water quality criteria in China. The regression analysis of pesticides toxicity differences indicated a decrease in LC 50 /EC 50 values (for Oncorhynchus mykiss and Carassius auratu) with the increase in molecular weights of pesticides. Pesticides with larger MWs might be more toxic to aquatic species. Similar trend was also observed in the regression analysis of a decrease in both American and Chinese HC 5 values for with increase of the number of containing halogen atoms. It indicated the potency of these parameters to be used to predict the ecotoxicity of pesticide. • HC 5 s of partial pesticides between China and America are dramatically different. • A positive correlation was revealed between pesticide ecotoxicity vs. MW. • Pesticide HC 5 values is negative to the number of containing halogen atoms. [ABSTRACT FROM AUTHOR]

The rainbow trout is a cold-water fish cultured in China. Heat stress has a serious impact on the summer survival and the yield of rainbow trout. A better understanding of the regulatory response of rainbow trout to heat stress will help in determining the relationship between heat stress signaling pathways and adaption mechanisms and help contribute to breeding new high-temperature tolerant strains of rainbow trout. In this study, the 48-h median lethal temperature (48h-LT 50) of rainbow trout was determined as 22.5°C. We developed control (16°C) and heat-treated (22.5°C) groups and extracted RNA from the head kidney tissues for high-throughput sequencing to study the microRNA (miRNA) expression profiles. Twelve up-regulated and five down-regulated miRNAs were identified between the control and heat-treated groups. A total of 22 target genes were predicted for 6 of the differentially expressed miRNAs, including 31 negative miRNA–mRNA interactions. Important regulatory pathways under heat stress are related to the metabolism and immune responses of the rainbow trout. Our findings provide preliminary data for investigating the high-temperature molecular mechanism of the rainbow trout and can help producers to reduce the economic losses caused by high temperature weather. • 48 h median lethal temperature (48h-LT 50) of rainbow trout was determined as 22.5°C. • 12 up regulated and 5 down regulated miRNAs were associated with regulation of heat stress in rainbow trout. • Important regulatory pathways under heat stress are related to the metabolism and immune responses of the rainbow trout. [ABSTRACT FROM AUTHOR]

Salmonid larvae, especially rainbow trout larvae, are suffering from disease caused by infectious hematopoietic necrosis virus (IHNV) with high mortality worldwide. As well, IHNV strains had been isolated from rainbow trout in China and caused huge loss. Since there had been no commercial vaccine to control IHNV outbreaks in China, a DNA vaccine encoded glycoprotein based on a local isolated IHNV strain was developed with a series of CpG sequence used as adjuvant, and the protection of the vaccine under natural culture condition was carried out. As a result, a high survival rate of 85% was obtained in vaccinated fish compared with 60% in untreated group after a serious nature infection. An innate immune response was induced in the early state of infection represented by significant up-regulations of Mx-1 and IFN-γ , resulting in a low IHNV load in vaccinated fish. Moreover, specific antibody of IgM and neutralizing antibody (NAb) was provoked after the vaccination and expressions of CD4 and CD8 were gradually increased. These results suggested that both innate and adaptive immunity were induced by the DNA vaccine during the field trial, which may guide for further control of IHNV outbreaks in farm rainbow trout culture. • The IHNV DNA vaccine was developed with a novel local strain isolated in Gansu. • Partial protection rate was obtained under natural farm conditions. • IHNV load was controlled to a low level by vaccination. • An overall immunity with both innate and adaptive immunity was activated. [ABSTRACT FROM AUTHOR]

Using species outside Salmonidae to prepare salmon products has been widely revealed as a new type of fraud in China and other countries with less stringent labeling stipulations, highlighting the necessity to establish proper methods for rapid screening of Salmonidae ingredient. The present work selected mitochondrial Cytb gene as the target, and developed a novel mini-DNA barcoding assay to identify the salmonids ingredient in processed fish products. Results showed that the novel method is highly specific for salmonids detection and only the seven common salmonids species were successfully amplified. With the inclusion of HRM analysis, we can make an accurate differentiation of Salar salar , Oncorhynchus mykiss , and the other wild-caught Oncorhynchus species, which are deep in the scandal of species mislabeling. Moreover, a closed-tube visual detection can also be achieved by the preaddition of HNB (hydroxyl naphthol blue) and SYTO 9 in the reaction mixture, allowing an easy and rapid way to distinguish positive from negative. Finally, the novel assay was successfully applied on commercial products and the absence of salmonids ingredient indicated mislabeling with 4 commercial products. Overall, mini-DNA barcoding is a robust tool for fish species identification and the novel method is effective in screening Salmonidae ingredient. [Display omitted] • The novel MDB method is highly specific for salmonids detection. • HRM can differentiate S. salar , O. mykiss , and other wild-caught Oncorhynchus species. • The visual method enables a simple way to distinguish positive and negative results. • The absence of salmonids ingredient indicates mislabeling with 4 salmon products. [ABSTRACT FROM AUTHOR]

Crossbreeding is a common technical approach for the development of new commercial fish strains characterized by high performance and a short generation time, for the Chinese market. Here, five strains - Bohai, Denmark, Donaldson, Norway, and California - of rainbow trout were used in a complete diallel cross, along with self-breeding within each strain, to estimate general combining ability; specific combining ability ( SCA); and linebred, maternal, and reciprocal effects. These strains were defined based on their location of origin; the Bohai strain was domesticated and has been maintained since 1959 by the Bohai cold-water fish experimental station in China. Applying univariate and multivariate genetic analyses for body weight using the data set from this complete diallel cross experiment, we found that the cross combination with the Donaldson strain exhibited the most positive growth performance, whereas the Bohai ♀ × Donaldson ♂ cross was the highest performing cross combination in the experiment. Multiple significance tests showed that 40% (4 of 10) of the significant SCA based on univariate analyses ( P < 0.05) were not significant based on multivariate analyses ( P > 0.05). These results suggested that multivariate genetic analyses may provide more reliable reference guidelines for decision making by managers of breeding programs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Products 6PPD-Q, 4-DBAP and 4-HDPA were detected in 6PPD water solutions. • 6PPD-Q hydrolysis half-lives (12.8–16.3 d) were longer than 6PPD (4.83–64.1 h). • For chiral 6PPD and 6PPD-Q, no enantioselective hydrolysis and conversion occurred. • 6PPD was highly toxic to G. rarus , and 6PPD-Q was "very highly toxic" to O. mykiss. • S -6PPD-Q toxicity was 2.6 times higher than R -6PPD-Q to O. mykiss. As a ubiquitous tire antidegradant, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) is persistently released into the environment. It is highly toxic to aquatic organisms, and its transformation product 6PPD-quinone (6PPD-Q), is "very highly toxic" to Oncorhynchus kisutch at a median lethal concentration (LC 50) of < 0.1 ng/mL. Notably, 6PPD and 6PPD-Q are chiral compounds. Here, enantioselective evaluations, including hydrolysis and acute toxicity were conducted after preparing the enantiomer, confirming the enantiomer absolute configuration and establishing enantioseparation methods. In the 6PPD hydrolysis experiments, the products 6PPD-Q, phenol, 4-[(1,3-dimethylbutyl)amino]- (4-DBAP) and 4-hydroxydiphenylamine (4-HDPA) were detected. In different water solutions, the hydrolysis of 4-DBAP and 4-HDPA was very fast (0.87–107 h), while the 6PPD-Q hydrolysis half-lives (12.8–16.3 d) were significantly longer than 6PPD (4.83–64.1 h). At the enantiomeric level, no enantioselective hydrolysis and conversion occurred. R -6PPD generated R -6PPD-Q, and S -6PPD generated S -6PPD-Q, and the formation rate of S -6PPD-Q was 1.77 times faster than R -6PPD-Q. In terms of the enantioselective toxicity, the 6PPD enantiomer was highly toxic to China-specific Gobiocypris rarus (LC 50 , 162–201 ng/mL), and it had no enantioselective difference. 6PPD-Q was "very highly toxic" (LC 50 , 1.66–4.31 ng/mL) to Oncorhynchus mykiss , which is of commercial importance, and the toxicities of rac -6PPD-Q and S -6PPD-Q were 1.9 and 2.6 times higher than R -6PPD-Q. Furthermore, the formation concentrations of S -6PPD-Q and R -6PPD-Q in 6PPD water solutions were higher than the LC 50 values of O. kisutch and O. mykiss , and the toxicity of 6PPD-Q was highly species-specific, which should raise concern. These results provide important information for environmental risk assessments of 6PPD and 6PPD-Q, especially from the perspective of enantiomers. [ABSTRACT FROM AUTHOR]

Weissellosis of rainbow trout is caused by the Gram-positive bacteria Weissella ceti and has been reported in China, Brazil and the United States. This disease can result in high mortality in market-sized fish and thus can cause significant economic loss. Thus far, phenotypic characterization and 16 S r RNA sequencing have been used to confirm a Weissellosis diagnosis. Here, we present the development of PCR-based diagnostic tools for the rapid identification and quantification of W. ceti within bacteriological culture and infected tissues. A duplex PCR, which amplifies both genus- and strain-specific targets, positively identifies isolates as W. ceti NC36. A q PCR assay was also developed to quantify pathogen load from infected tissues, using a W. ceti NC36 unique locus. A proof of concept study was performed to demonstrate that quantification using traditional plate count methods and q PCR were significantly correlated when assessed from infected brain and spleen tissue. These tools were also used to confirm diagnosis of Weissellosis in a commercial rainbow trout farm during an outbreak investigation. These are the first diagnostic tools developed for identification and quantification of W. ceti infection within rainbow trout, contributing to rapid Weissellosis diagnosis, enhanced pathogen surveillance and epidemiological studies. Significance and Impact of the Study Weissellosis is a rapidly emerging infectious disease of farmed rainbow trout caused by Weissella ceti, a Gram-positive lactic-acid bacterium. This disease can cause significant economic loss, and thus, efforts to limit its spread are urgently needed and are dependent on the development of diagnostic tools. The article presents the development of PCR-based diagnostic assays for the rapid identification of W. ceti and for quantification of pathogen load directly from tissues without the need for bacterial amplification or isolation. These tools are critical for rapid confirmation of Weissellosis diagnosis and for studying the epidemiology of this emerging pathogen. [ABSTRACT FROM AUTHOR]

The variance components of additive effects and genetic correlations of body weight (BW) and body measurement traits were estimated in a freshwater strain selected for large size in a breeding program for rainbow trout, Oncorhynchus mykiss, in China. Phenotypic data were collected for BW and measurement traits from 2362 individuals with a two-generation pedigree, and the average information-restricted maximum likelihood method was used for the genetic analysis. The genetic parameters of BW were estimated at three time points (550, 850, and 1000 days post-fertilization [dpf]), showing high heritability in a range from 0.33 to 0.98. However, the heritability estimates of total length (TL) showed lower values ranging from 0.05 to 0.51, with high standard errors. Genetic correlation between TL and BW was almost equal to unity at 550 dpf, and the genetic correlations between TL at 550 dpf and BW at two other time points were all positive and very high (ca. 0.95-0.99). These results indicate that BW and TL selected at 550 dpf had a direct positive effect on BW performance at 1000 dpf, which was 450 d before the date of the target trait observed. [ABSTRACT FROM AUTHOR]

Salmonid are farmed far offshore in a submersible cage in China, and air supplementation in the swim bladder is an important issue while the fish are confined in the submersed cage. The objective of this study is to test the effects of different types of air supplementation on the growth, energy budget, and fatty acid composition of the rainbow trout, Oncorhynchus mykiss , confined underwater. The fish were divided into four groups with four replicates (63.84 ± 2.03 g, 13 fish per tank): The control group fish (Ctrl) were cultured in a glass fiber tank with airstone; The mesh group (ME) used a net in a tank to keep the experimental fish from the water surface, and an airstone above the net; The airstone group (AM) added an airstone under the net; And the airdome group (DM) added an airdome under the net. At the end of a 35-day trial, the final mean weight (70.00 ± 1.63 g), percent weight gain (7.09 ± 0.96%) and survival rate (76.92 ± 0.00%) of the fish in ME group were significantly lower than those in Ctrl group (91.54 ± 5.19 g, 43.49 ± 10.35% and 100.00 ± 0.00%, respectively). The final mean weight of AM group was significantly lower than that of Ctrl group, whereas there were no significant differences in other growth indexes between control group, DM and AM group. The proportion of feeding energy allocated to growth in ME group was the lowest, the proportion in AM was significantly higher than ME group and lower than Ctrl group, and there was no significant difference between those in DM and Ctrl groups. The muscle saturated fatty acid level in Ctrl group was significantly lower than those in other groups. In conclusion, the growth of rainbow trout confined underwater for 35 days will slow down due to lower proportion of feeding energy allocated to growth and higher proportion to respiration. The addition of an airdome or airstone can partially compensate for the growth of the fish confined underwater long time. Rainbow trout confined underwater can partially compensate for the loss of buoyancy through increasing the muscle saturated fatty acid content. • Removing surface access for rainbow trout is not feasible, and an air-dome or bubbling partially solved the swim bladder air loss issue from long-term diving. • The empty swim bladder leads to the increase of crude fat content and saturated fatty acid ratio in muscle. • The effects of airdomes, also combined with larger bubble airstone on the growth of salmonid fish need to be studied further. [ABSTRACT FROM AUTHOR]

Abstract: Species sensitivity distributions (SSDs) are usually used in the development of water quality criteria and require a large number of toxicity values to define a hazard level to protect the majority of species. However, some toxicity data for certain chemicals are limited, especially for endangered and threatened species. Thus, it is important to predict the unknown species toxicity data using available toxicity data. To address this need, interspecies correlation estimation (ICE) models were developed by US EPA to predict acute toxicity of chemicals to diverse species based on a more limited data set of surrogate species toxicity data. Use of SSDs generated from ICE models allows for the prediction of protective water quality criteria, such as the HC5 (hazard concentration, 5th percentile). In the present study, we tested this concept using toxicity data collected for zinc. ICE-based-SSDs were generated using three surrogate species (common carp (Cyprinus carpio), rainbow trout (Oncorhynchus mykiss), and Daphnia magna) and compared with the measured-based SSD and corresponding HC5. The results showed that no significant differences were observed between the ICE- and the measured-based SSDs and HC5s. Furthermore, the examination of species placements within the SSDs indicated that the most sensitive species to zinc were invertebrates, especially crustaceans. Given the similarity of SSD and HC5s for zinc, the use of ICE to derive potential water quality criteria for diverse chemicals in China is proposed. Further, a combination of measured and ICE-derived data will prove useful for assessing water quality and chemical risks in the near future. [Copyright &y& Elsevier]

The article presents abstracts on industrial ecology which include the integration of environmental considerations into management-related decision making, a dynamic material flow analysis for strategic construction and demolition waste management in Beijing, China and evaluation of the Chinese tire industry with the use of physical input-output analysis.

Abstract: Six strains of Gram-positive, catalase-negative, non-motile, irregular short rod-shaped Weissella bacteria, with width and length of 0.5–0.6 and 1.2–2.7μm were isolated from diseased rainbow trout Oncorhynchus mykiss (Walbaum) in winter of 2007 at a commercial fishery in Jingmen, Hubei province, China. The diseased rainbow trout exhibited hemorrhage in eyes, anal region, intestine and abdomen wall, petechia of liver, some fish with hydrocele in stomach. Six isolates had identical biochemical reactions, phylogenetic analysis of 16S rDNA sequences, amplified ribosomal DNA restriction analysis (ARDRA), enzymatic profile analysis and antimicrobial susceptibility results, indicating as a single clonal outbreak. But all were different from any other validated twelve Weissella species in the term of physiological and biochemical characters. It is indicated that isolates are phylogenetically closer to Weissella halotolerans, Weissella viridescens and Weissella minor on 16S rDNA phylogenetic analysis result, than to W. halotolerans and W. viridescens on the result of ARDRA study and enzymatic profile analysis. Antimicrobial susceptibility testing was used to scan effective drugs for the therapy of this disease. Experimental infection assays with one isolate were conducted and pathogenicity (by intraperitoneal injection) was demonstrated in rainbow trout O. mykiss (Walbaum) and crucian carp (Carassius auratus gibelio) fingerlings. Because no Weissella was detected in fish feedstuffs and pond water, the source of this pathogen remains unknown, and Weissella isolates were regarded as an opportunistic pathogen for rainbow trout. This is the first report of Weissella strains which can cause disease of cultured fish in the world. [Copyright &y& Elsevier]

Although fish feed supplemented with Chinese parsley (CP), Coriandrum sativum, does not affect the health of rainbow trout Oncorhynchus mykiss, it has the remarkable effect of reducing the uptake of Cd (12–17% compared with controls without CP). Here, we measured the change in the amount of metallothionein (MT) in the liver and kidney using gel permeation chromatography-high-performance liquid chromatography (TSK GEL SW 3000 column). The increase in MT content over time in the Cd-fed groups corresponded to the change in Cd accumulation. Gel permeation was performed with soluble fractions from the fish liver and kidney, and changes in the Cd, Cu, and Zn concentrations over time for each fraction, and the relationship between the form of Cd that accumulated in tissues and its toxicity were measured. A nontoxic MT fraction of 7,000 Da and a high-molecular-weight fraction of approximately 60,000 Da were isolated from the soluble fractions. The induction of nontoxic MT–Cd was higher in the CP-supplemented groups than in the control groups. The synergetic actions of several compounds in CP may contribute to bind MT, thereby preventing accumulation of harmful heavy metals and essential metals in fish. [ABSTRACT FROM AUTHOR]

Rainbow trout (Oncorhynchus mykiss) is an important economic fish in China. Skin color affects the economic value of trout. However, the molecular mechanism of the skin color variation between wild-type (WR) and yellow mutant rainbow trout (YR) is unclear. We sequenced mRNAs and miRNAs of dorsal skin to identify key color variation-associated mRNAs and miRNAs between WR and YR. Overall, 2060 out of 3625 differentially expressed genes were upregulated in YR, and 196 out of 275 differentially expressed miRNAs were downregulated in WR. We identified three key YR-upregulated genes related to the formation of xanthophores (GCH1 , SLC2A11 , and SOX10). Interestingly, several genes related to melanogenesis (TYR , TYRP1 , TYRP2 , MC1R , MITF , PMEL , SLC45A2 , and OCA2) were downregulated in WR. Integrated analysis identified five miRNAs that target at least two skin color-related genes (miR-495-y, miR-543-y, miR-665-z, miR-433-y, and miR-382-x). Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses of target genes identified noncoding RNA metabolic process as the most significantly enriched GO term, and several metabolic pathways associated with skin color were enriched significantly, such as tyrosine metabolism, histidine metabolism, and vitamin B6 metabolism. Quantitative real-time PCR of selected mRNAs and miRNAs validated the reliability of the integrated analysis. This study provides in-depth insights into the molecular mechanism of skin color variation between WR and YR, which will accelerate the genetic selection and breeding of rainbow trout with consumer-favored traits. [Display omitted] • Comparative mRNA and miRNA expression was firstly conducted to identify key mRNAs and miRNAs that may be responsible for skin color variation between wild-type and yellow mutant rainbow trout. • Three key positive genes in the formation of xanthophores and several important genes related to melanogenesis were all up-regulated in yellow mutant rainbow trout. • Five miRNAs were identified that target at least two skin color related genes. • Several metabolic pathways related to skin color were significantly enriched. [ABSTRACT FROM AUTHOR]

The article presents a study which focuses on determining the origin of Gyrodactylus brachymystacis Ergens on farmed rainbow trout (Oncorhynchus mykiss) and the seasonal occurrence of an infection on wild Manchurian trout (Brachymystax lenok) in central China. This study, which was conducted at a private fish farm on the Shibianyu River in the Qinling Mountains, examines the prevalence of the infection and determined the mean number of parasites on the different body sites and fins. The spatial distribution of the parasites over the body surfaces is also analyzed.

The article presents a study which describes the history of rainbow trout parasites at a fish farm in Qinling Mountains, China. It has discovered intense infections of monogeneans known as gyrodactylus brachymystacis. The rainbow trout was infected with a parasite that originated from a host fish in the country that led to chronic gyrodactylosis. The morphology and molecular taxonomy of the said parasite are also discussed.

Passive virus surveillance was performed in twenty-nine salmon and trout farms from seven provinces and districts in China during the period 2017–2020. A total of 25 infectious pancreatic necrosis virus (IPNV) isolates were obtained, mainly from rainbow trout (Oncorhynchus mykiss). The molecular evolution of these Chinese IPNV isolates and the previously reported Chinese IPNV strains ChRtm213 and WZ2016 was analyzed, based on their VP2 gene coding region sequences (CDS). All 27 Chinese IPNV isolates clustered within genogroups I and V, with 24 of the IPNV isolates belonging to genogroup I (including ChRtm213 and WZ2016), and only three isolates clustering in genogroup V. The Chinese genogroup I IPNV isolates lacked diversity, composing six haplotypes with 41 polymorphic sites, and the identity of nucleotide and amino acid sequences among the entire VP2 gene CDS from these isolates was 97.44%–100% and 98.19%–100%, respectively. Divergence time analyses revealed that the Chinese genogroup I IPNV isolates likely diverged from Japanese IPNV isolates in 1985 (95% highest posterior density (HPD), 1965–1997), and diverged again in 2006 (95% HPD, 1996–2013) in China. Each of the three Chinese genogroup V IPNV isolates has a unique VP2 gene CDS, with a total of 21 polymorphic sites; the identity of nucleotide and amino acid sequences among all VP2 gene CDS from these isolates was 98.5%–99.5% and 98.6%–99.0%, respectively. The data demonstrate that genogroups I and V are more likely the currently prevalent Chinese IPNV genotypes. [ABSTRACT FROM AUTHOR]

The co-infection of infectious hematopoietic necrosis virus (IHNV) and infectious pancreatic necrosis virus (IPNV) with high mortality was observed in farmed rainbow trout (Oncorhynchus mykiss) in China. Severe extensive necrosis was observed on the major organs of moribund rainbow trout, and tissue fluid from diseased fish was able to cause obvious cytopathic effect in CHSE-214 cells. The co-infection of IHNV and IPNV was detected by RT-PCR and confirmed by an immunofluorescent assay test. The IHNV and IPNV in this co-infection had the same genogroups as the currently prevalent IHNV and IPNV strains in China, and they belonged to genogroup J and genogroup 1, respectively. Distinct from previous studies, the IHNV loads were significantly higher than the IPNV loads in both co-infected tissues and viral cell culture suspension (p < 0.05). Furthermore, the tissue suspensions and cell culture suspensions (cells directly inoculated with pooled tissues suspension from infected fish) were very virulent, causing cumulative mortalities of 94% and 96% in rainbow trout that were challenged at a standard dosage of 100 half tissue culture infective doses (TCID 50). Similar high mortality was observed from rainbow trout challenged with purified IHNV, indicating mortality caused by natural co-infected samples may be solely attributable to IHNV, with no apparent impact from the IPNV in the co-infected sample. However, significantly decreased mortality was obtained from the artificial co-infection performed by challenging rainbow trout with a mixture of purified IHNV and purified IPNV at a 1:1 ratio. Notably, viral interference was not detected in this natural co-infection case, even though it could be observed in fish challenged with the purified viruses from the natural infection sample, indicating that IHNV and IPNV co-infection is far more complicated than previously understood. It is urgent to pay more attention to viral interactions to improve the systematic prevention and control of fish diseases. • IHNV and IPNV co-infection with high mortality in China was firstly reported. • Viral interference was not observed in this natural co-infection. • IHNV loads were far higher than the IPNV loads in the natural co-infection. • The IHNV and IPNV belong to genogroup J and genogroup 1, respectively. [ABSTRACT FROM AUTHOR]

Brachymystax lenok is a cold freshwater fish accustomed to inhabit relatively high concentration of dissolved oxygen and clean upper streams. Here we present 13 polymorphic microsatellite primer pairs from rainbow trout to amplify in 32 B. lenok individuals from Ussuri River of China. The number of alleles ranged from two to seven with an average of 3.9 per locus. Observed heterozygosity ranged from 0.0625 to 0.9677. One locus showed significant deviation from Hardy–Weinberg equilibrium. These 13 loci will provide a good basis for investigation of B. lenok population structure and genetic diversity in different distribution region. [ABSTRACT FROM AUTHOR]