Cyprinid Species Research Articles

De novo RNA-seq assembly and differential transcriptome analysis of Carassius auratus gibelio after Cyprinid herpesvirus 2 infection

Carassius auratus gibelio, in the family Cyprinidae, is one of the most popular freshwater aquaculture species in China. The infection of domestic cyprinid species by Cyprinid herpesvirus 2 (CyHV-2) causes herpesvirus hematopoietic necrosis (HVHN). Until now, the pathogenic mechanism of CyHV-2 has been unclear. In this study, we used RNA sequencing to investigate the gene expression patterns in C. auratus gibelio after CyHV-2 infection. We identified 163,365 unigenes with de novo transcriptome sequencing using the Trinity and TGICL software. In total, 8011 differentially expressed genes (DEGs) were identified in the CyHV-2-infected fish vs healthy fish, 4170 of which were upregulated and 3841 downregulated. A Gene Ontology (GO) analysis showed that most of the DEGs functioned in the cellular hyperosmotic response, inflammatory response, creatine: sodium symporter activity, voltage-gated potassium channel complex, complement activation, and oxygen binding categories. A Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that the top five KEGG pathways enriched in upregulated genes were neuroactive ligand-receptor interaction, pyrimidine metabolism, IL-17 signaling pathway, glutathione metabolism, and arginine biosynthesis. The top five KEGG pathways enriched in downregulated unigenes were cytokine–cytokine receptor interaction, complement and coagulation cascades, Staphylococcus aureus infection, drug metabolism, and glycine, serine, and threonine metabolism. The expression of five key immunity-related genes was confirmed with real-time PCR. Specifically, the genes encoding interleukin-11 and interleukin-13 receptor, which are involved in immunity, were significantly upregulated and downregulated in CyHV-2-infected fish, respectively. Our findings not only extend our understanding of the host's response to CyHV-2, but also clarify the molecular pathogenicity mechanisms involved.

<i>Pethia arunachalensis</i>, a new species of small barb (Teleostei: Cyprinidae) from Arunachal Pradesh, India

Pethia arunachalensis, a novel cyprinid species, is described from the Nao-dhing River, Brahmaputra Basin, Arunachal Pradesh, India. The new species is diagnosed in having an incomplete lateral line, 6-7 lateral-lined pored scales, absence of barbels and a distinct black caudal spot. A key to the species of the genus Pethia established in the Ganga-Brahmaputra drainage is provided.

Histopathology and immunohistochemistry of gills of Van fish (Alburnus tarichi Güldenstädt, 1814) infected with myxosporean parasites

ABSTRACT The Van fish are a cyprinid species endemic to Turkey’s largest soda lake, Lake Van, and have great economic value because they are a food source. Once a year, the fish take part in reproductive migration to the fresh waters flowing into the lake. The fish migrate from an extreme environment with high salinity (2.2%) and high pH (9.8). These fish are unable to reproduce in this alkaline environment and must migrate to fresh water during their breeding season. The aim of the present study is to report the presence of the myxosporean parasites on the gills and the pathological changes. Changes in gill histopathology, mucocytes, mitochondria-rich cells, expression of Heat Shock Protein 70 (Hsp70), and ATPase (NKA) were observed in the gill tissue. As a result of the histopathological changes in gills, infected fish had abundant plasmodia with different sizes. Plasmodia were found on gill filaments inside white ovoid-shaped structures. It was observed that plasmodia were contained on the primary filament which changed the histological structure of the gill tissue to a large extent. It was determined that the density and size of mucocytes in the infected areas of the gill tissue increased, whereas the number of mitochondria-rich cells decreased. Hsp70, an indicator of stress, was not different between normal and infected fish.

Genetic structure of natural populations of endangered Tor mahseer, Tor tor (Hamilton, 1822) inferred from two mitochondrial DNA markers

Tor tor, Tor mahseer, an endangered cyprinid species, is important as a sport fish. Genetic divergence in natural populations of T. tor was investigated using two mitochondrial genes, Cytb (Cytochrome b) and ATPase6/8. Analysis of 140 sequences of Cytb (1121 bp) and ATPase6/8 (842 bp) genes revealed 12 and 7 haplotypes, respectively, whereas 23 haplotypes were found in concatenated sequences (1963 bp). Sequence analysis of mitochondrial regions revealed balancing selection and displayed low nucleotide and moderate haplotype diversities. Mantel tests identified a positive relationship between pairwise geographical and genetic distances for the study region. Results of AMOVA based on genes pointed out that the genetic variations were mainly due to variation in within populations (ATPase6/8: 62.73%, Cytb: 42.13%, concatenated sequences: 48.31%). The total Fst was found to be significant in both genes with a value of 0.5787 (p <0 .05) and 0.3726 (p <0 .05) for Cytb and ATPase6/8genes respectively, whereas 0.51687 (p <0 .05) was found in combined sequences, which revealed sub-structuring in the T. tor natural populations. Population pair-wise Fst ranged from 0.00901– to 0.85631 for Cytb and 0.09910– to 0.64731 for ATPase6/8genes, whereas 0.02039 to 0.85436 in combined sequences. Results indicated the presence of four genetic stocks in the populations studied. The baseline information about stock characterisation in this study would be applicable for planning strategies for conservation, management and sustainable fisheries of this species.

Transcriptome analysis in the skin of Carassius auratus challenged with Aeromonas hydrophila

Skin plays an important role in the innate immune responses of fish, particularly towards bacterial infection. To understand the molecular mechanism of mucosal immunity of fish during bacterial challenge, a de novo transcriptome assembly of crucian carp Carassius auratus skin upon Aeromonas hydrophila infection was performed, the latter with Illumina Hiseq 2000 platform. A total of 118111 unigenes were generated and of these, 9693 and 8580 genes were differentially expressed at 6 and 12 h post-infection, respectively. The validity of the transcriptome results of eleven representative genes was verified by quantitative real-time PCR (qRT-PCR) analysis. A comparison with the transcriptome profiling of zebrafish skin to A. hydrophila with regards to the mucosal immune responses revealed similarities in the complement system, chemokines, heat shock proteins and the acute-phase response. GO and KEGG enrichment pathway analyses displayed the significant immune responses included TLR, MAPK, JAK-STAT, phagosome and three infection-related pathways (ie., Salmonella, Vibrio cholerae and pathogenic Escherichia coli) in skin. To our knowledge, this study is the first to describe the transcriptome analysis of C. auratus skin during A. hydrophila infection. The outcome of this study contributed to the understanding of the mucosal defense mechanisms in cyprinid species.

Novel Mechanisms for IGF-I Regulation by Glucagon in Carp Hepatocytes: Up-Regulation of HNF1α and CREB Expression via Signaling Crosstalk for IGF-I Gene Transcription.

Glucagon, a key hormone for glucose homeostasis, can exert functional crosstalk with somatotropic axis via modification of IGF-I expression. However, its effect on IGF-I regulation is highly variable in different studies and the mechanisms involved are largely unknown. Using grass carp as a model, the signal transduction and transcriptional mechanisms for IGF-I regulation by glucagon were examined in Cyprinid species. As a first step, the carp HNF1α, a liver-enriched transcription factor, was cloned and confirmed to be a single-copy gene expressed in the liver. In grass carp hepatocytes, glucagon treatment could elevate IGF-I, HNF1α, and CREB mRNA levels, induce CREB phosphorylation, and up-regulate HNF1α and CREB protein expression. The effects on IGF-I, HNF1α, and CREB gene expression were mediated by cAMP/PKA and PLC/IP3/PKC pathways with differential coupling with the MAPK and PI3K/Akt cascades. During the process, protein:protein interaction between HNF1α and CREB and recruitment of RNA Pol-II to IGF-I promoter also occurred with a rise in IGF-I primary transcript level. In parallel study to examine grass carp IGF-I promoter activity expressed in αT3 cells, similar pathways for post-receptor signaling were also confirmed in glucagon-induced IGF-I promoter activation and the trans-activating effect by glucagon was mediated by the binding sites for HNF1α and CREB located in the proximal region of IGF-I promoter. Our findings, as a whole, shed light on a previously undescribed mechanism for glucagon-induced IGF-I gene expression by increasing HNF1α and CREB production via functional crosstalk of post-receptor signaling. Probably, by protein:protein interaction between the two transcription factors and subsequent transactivation via their respective cis-acting elements in the IGF-I promoter, IGF-I gene transcription can be initiated by glucagon at the hepatic level.

Availability of animal food organisms and their utilization by cyprinids in Sri Lankan hill-stream pools

The food and feeding of cyprinid fishes in three stream pools in South West Sri Lanka, was investigated from 29 June 1984 to 25 February 1986. S.W. Sri Lanka was chosen as a study site because the rainforest and its fish fauna are here severely threatened. Feeding ecology was studied by gut contents analysis. The availability of prey organisms in the environment was quantified and food utilization in each pool was estimated by comparing diet compositions of the fish species with the food availability. Seven cyprinid species represented more than 98% of the fish numbers caught. These were Pethia cumingii (PC), Puntius dorsalis (PD), Dawkinsia singhala (DS), Pethia nigrofasciata (PN), Systomus pleurotaenia (SP), Devario malabaricus (DM) and Rasbora daniconius (RD). Three of these species: the two surface feeders DM and RD and the generalist SP fed &gt; 33 % (biovolume) on terrestrial arthropods. Since we were not able to quantify the availability of terrestrial arthropods - mainly ants falling from the trees into the stream - these three species were not included in part of the analysis. Chironomid larvae were most abundant and, on basis of biovolume, the most important animal food items of the remaining four cyprinid species (PC, PD, DS, PN). PD and PN strongly positively selected chironomid larvae, but DS and PC only weakly negatively. Although coleopterans and ephemeropterans were after chironomid larvae the most abundant food items in the environment the former were often negatively selected and ephemeropterans positively, so that the latter were generally after chironomid larvae the most frequently eaten food items.

Phylogenetic and secondary RNA structure analysis of monogenean gill ectoparasites(Dactylogyrus spp.) parasitizing certain freshwater fishes.

The current study is the first phylogenetic and secondary RNA structure analysis of Dactylogyrus species parasitising gill filaments of Iraqi cyprinid fishes. Most previous phylogenetic studies have targeted on primary DNA sequence data. Nevertheless, RNA secondary configuration is principally helpful in systematics since they comprise features that do not appear in the primary sequence and provide morphological information. The primary objective was molecular-based identification of Dactylogyrids species using evolutionary tree and secondary RNA structure prediction. A total of 681 fish were collected from the Lesser Zab River in the northeast of Iraq in the sub-district of Altun-Kopru from August 2016 to September 2017 and brought to the Zoology Research Laboratory, Salahaddin University-Erbil, Iraq. All fish were classified as 18 cyprinid species. The species of Dactylogyrus were identified by the 28S rDNA subunit using PCR and sequencing methods, and the obtained nucleotide sequences were then compared with the available GenBank sequences. Phylogenetic relationships were concluded using Neighbour-Joining (NJ), Maximum Likelihood (ML), and Minimum Evolution (ME) methods. The results justify the validation of 11 Dactylogyrus species (three of them were newly recorded in Iraq). Additionally, out of nine infected fish species, seven of them were regarded as a new host for Dactylogyrus species. Secondary RNA configuration prediction using minimum free energy was considered as a hopeful tool for species identification. This was considered the first comprehensive phylogenetic study in the area. It was concluded that PCR sequencing, phylogenetic and secondary RNA analysis were proper molecular methods for identifying Dactylogyrids species on the gills of fishes.

Integrative study of population structure of Telestes dabar, the strictly endemic cyprinid species from the Dinaric karst on the Balkan Peninsula

Diversification of the genus Telestes (Cyprinidae), endemic to the Euro-Mediterranean biogeographic subregion, mirrored an evolutionary footprint of complex biogeographical history. Hence, hidden diversity and noticeably high endemicity of freshwater ichthyofauna were discovered in the Dinaric karst on the Balkan Peninsula. One such example includes two steno-endemic Dinaric karst (Bosnia and Herzegovina) cyprinid species, Telestes dabar and T. metohiensis. Although the conservation status of T. metohiensis has been evaluated, T. dabar from Dabarsko Polje has not yet been assessed for the IUCN Red List due to its taxonomically ambiguous position and data deficiencies. Our first aim was to evaluate the resolution of taxonomic ambiguities of the two putative species, T. dabar and T. metohiensis, by the complementary use of two mitochondrial DNA markers (cytb and COI mtDNA). The results clearly demonstrated the evolutionary independence of T. dabar (Dabarsko Polje) and T. metohiensis (Nevesinjsko Polje) and confirmed the usefulness of both markers for assessing the species borders. In addition, population structure of putative T. dabar was analyzed using cytb and COI mtDNA and morphological parameters (linear measurements and landmark-based geometric morphometric data). A high genetic admixture and homogeneity in T. dabar from Dabarsko Polje were found and confirmed using both morphometric approaches as no statistically significant differences were consistently registered between different samples.

Immunohistochemical analysis of pigment cell tumors in two cyprinid species.

Pigment cell tumors, also known as chromatophoromas, are cutaneous spindle cell neoplasms originating from pigment cells (chromatophores) in the dermis of teleosts, amphibians, and reptiles. Chromatophoromas share similar histologic morphology to other spindle cell tumors and are not always pigmented. Therefore, immunohistochemical analysis may be useful in distinguishing these neoplasms from tumors of other cellular origin when poorly pigmented. We performed 3 immunohistochemistry assays (PNL-2, melan A, and SOX10) on 8 cutaneous neoplasms from 8 teleosts diagnosed as chromatophoromas based on histologic morphology. Semiquantitative analysis of immunoreactivity was evaluated on each immunohistochemical assay using a 0-3 scale. PNL-2 exhibited mild-to-moderate (1 or 2) immunoreactivity in 7 of the cases, and resident chromatophores (internal control) were also immunoreactive in these cases. Melan A exhibited mild-to-moderate (1 or 2) immunoreactivity in 4 cases (and with resident chromatophores in these cases); SOX10 was not immunoreactive in any cases. Our results indicate that PNL-2 may be a useful marker in teleosts to distinguish tumors of chromatophore origin. Melan A could also be useful, but appears to be less sensitive, and SOX10 is likely not a useful marker for these neoplasms in teleosts.

Asian Fish Tapeworm (Schyzocotyle acheilognathi) Found in New York State for the First Time After a Long-Term Fish-Parasite Survey

The first report of Asian fish tapeworm (AFT), Schyzocotyle acheilognathi (Yamaguti, 1934) Brabec, Waeschenbach, Scholz, Littlewood and Kuchta, 2015, is provided for New York State. This finding resulted from a long-term fish parasite survey in various water bodies in Otsego County in central-east New York that took place during 2008–2018. In total, 1,637 individual fish representing 44 species were examined for AFT, with 4 (9%) of the 44 species of fish infected with S. acheilognathi. These 4 species were all cyprinids: Notemigonus crysoleucas (golden shiner), Notropis heterodon (blackchin shiner), Pimephales promelas (fathead minnow), and Semotilus atromaculatus (creek chub). Among these host species, the prevalence of Schyzocotyle acheilognathi was highest in Notemigonus crysoleucas, with 19 (15.7%) of 121 fishes infected. The infection in Notropis heterodon constitutes a new host record for S. acheilognathi. The observed occurrence of S. acheilognathi only in cyprinid species was generally consistent with previously reported infection patterns for this cestode, but we note that AFT was absent from multiple fish species in our survey that had elsewhere been reported as hosts. The source of AFT for water bodies in Otsego County, New York is unknown, but bait-bucket introduction of infected Notemigonus crysoleucas is considered a possible explanation. This study contributes to a growing body of molecular data for this highly invasive tapeworm by providing sequence data for 2 markers (large ribosomal subunit, 28S, and cytochrome c oxidase I) for 6 specimens.

Strip Spawning Methodology for Captive Propagation of Broadcast‐Spawning Cyprinids in the Great Plains

AbstractIn the summer of 2011, large parts of Texas and Oklahoma experienced their worst drought in recorded history. Most of the rivers and streams in this region are inhabited by cyprinids that broadcast semibuoyant pelagic ova. These fish depend on flowing water for the hormonal cues that induce spawning and to allow ova to develop and hatch as they float downstream. During the drought, the Brazos and Canadian rivers, Texas, were reduced to isolated streambed pools. Monitoring efforts concluded that pelagic, broadcast‐spawning cyprinids experienced complete reproductive failure in the Brazos River and had very little spawning success in the Canadian River. Personnel from the Texas Parks and Wildlife Department, U.S. Fish and Wildlife Service, and Texas Tech University began salvage operations in both rivers in September 2011 to ensure the survival of imperiled cyprinids. In spring 2012, standard captive propagation techniques were used with several species of cyprinids, with little success. As a result, we developed new techniques for four species of pelagic, broadcast‐spawning cyprinids from the Brazos and Canadian rivers that could greatly increase hatchery program efficacy.

Perforin-expressing IGT+ B cell with cytotoxic activity, a novel player in the innate immune response of teleost fish

We have monoclonal antibodies (mAbs) against CD4-1 (6D1) and CD8α (2C3) in ginbuna crucian carp Carassius auratus langsdorfii. In our previous studies we showed that 2C3 mAb positive cells are the primary cell type showing specific cytotoxicity against allogeneic targets, suggesting that CD8α+ lymphocytes in ginbuna are equivalent to cytotoxic T lymphocytes (CTLs) in mammals. We further demonstrated the helper T cell function of 6D1 mAb positive cells by studying mixed leukocyte culture (MLC) and hapten/carrier effects. Here, we report that our mAbs cross-react with zebrafish lymphocytes. First, mAbs 6D1 and 2C3 recognized 7–11% of zebrafish lymphocytes that were ZAP-70 positive and had the typical morphology of lymphocytes. Second, to verify the cell types reacting with the 6D1 and 2C3 mAbs we examined the expression profiles of zebrafish lymphocyte surface markers in FACS-sorted lymphocytes from kidney. cd4-1 (cd8a) and tcrac but not iglc transcripts were detected in 6D1(2C3)+ lymphocytes, whereas cd4-1 (cd8a) transcripts were not found in 6D1 (2C3)- lymphocytes. Third, we further confirmed that 6D1 reacted with zebrafish CD4-1 but not CD4-2, and 2C3 recognized zebrafish CD8α expressed on HEK293T cells. Collectively, these findings suggest that 6D1+ and 2C3+ lymphocytes in zebrafish are equivalent to CD4+ and CD8α+ T lymphocytes in mammals, respectively. Furthermore, we found the cross-reactivity of our 6D1 and 2C3 mAbs with other cyprinid species including goldfish, common carp and grass carp.

An outline of the biology, distribution, and conservation of Neretva nase, Chondrostoma knerii (Actinopterygii: Cypriniformes: Cyprinidae), endemic to the Neretva River basin (Croatia and Bosnia and Herzegovina)

Background. The Neretva nase, Chondrostoma knerii Heckel, 1843, is an endemic cyprinid species distributed in the Neretva River basin in Croatia and Bosnia and Herzegovina, designated in the EU Habitats Directive as a species requiring conservation within member states. According to the IUCN, the species is catalogued as vulnerable (VU). Available scientific data indicate that significant aspects of its biological and ecological characteristics, as well as conservation requirements, are scarce and largely composed of outdated records. This paper provides a summary of the main life history traits, particularly those related to the conservation challenges and a detailed list of the current state of knowledge. Materials and methods. This review was based on published literature in the form of research articles, monographs, books and technical reports, as well as unpublished data Results. All available data were organized, critically analysed and presented in a comprehensive form. Issues related to species conservation were highlighted with respect to the impact of development activities. The long-term monitoring data of reproduction activity in the Hutovo Blato wetland were presented, showing the lowering of spring inflow capacity as the major factors for spawning success. Conclusion. This review will, hopefully, serve as foundation and indicative example for future research aimed at better understanding the origin and status of this fish species in order to assure effective management and conservation programs.

The genetic diversity, individual relatedness and possible mating system of an isolated population of the Cyprinid species Megalobrama pellgrini in upper reaches of the Changjiang (Yangtze) River, China

Megalobrama pellegrini is a cyprinid fish endemic to upper reaches of the Changjiang (Yangtze) River, China, which is also an important economic species in the local area. In recent years, resources of this species have decreased sharply and its conservation has drawn great attention. In the present study, we collected 120 individuals from the Longxi River, a tributary isolated from the main channel of the Changjiang River, where M pellegrini is still relatively abundant. Using two different molecular markers, mitochondrial cytochrome b (cyt b) gene, and nuclear microsatellite (simple sequence repeat, SSR), we analyzed the genetic diversity of this isolated population. The results show that sequence genetic diversity was low (Hd: 0.290 and Pi. 0.000 77 for cyt b gene), while the SSR genetic diversity was high (Ho: 0.824 4±0.147 2, He: 0.823 5±0.145 1). Analysis indicated that this population had experienced a bottleneck, with inbreeding and small effective population size (around 50). Based on SSR data, relatedness analyzing revealed that the 120 samples were grouped into 10 completely independent clusters. It was inferred that the mating system of M pellegrini was polygamy. We suggested that the low genetic diversity could be induced by the overfishing and inbreeding depression. Therefore, we suggested that the urgent conservation measures should be taken to control the overfishing and give better conditions for the fish to grow and spawn, then to restore population size.

Transcriptome analysis of rare minnow (Gobiocypris rarus) infected by the grass carp reovirus

Grass carp shares the largest portion of the aquaculture production in China, but hemorrhagic disease caused by grass carp reovirus (GCRV) often results in tremendous loss of fingerlings and yearlings, causing significant economic damages. However, it is difficult to study antiviral mechanisms in grass carp in vivo due to its large size and long reproductive cycle. Therefore, a small cyprinid species named rare minnow with high sensitivity to GCRV, is regarded as a useful model to study the mechanisms of this disease. In this study, rare minnows were infected with the type-IIGCRV (GCRV-HZ08), and pathogenesis was investigated by BGISEQ-500 transcriptome sequencing of four cDNA libraries, hepatopancreas, gills, head-kidney and spleen, and real time quantitative PCR (qRT-PCR). We obtained 51.22 Gb bases in total, and de novo assembled 107,756 unigenes with an average length of 1,441 bp. GO analysis revealed that the differentially expressed genes (DEGs) involved in the defense mechanisms were the most enriched GO terms in all four tissues. KEGG analysis revealed that the most enriched pathways were “Influenza A”, “Herpes simplex infection”, “Transcriptional misregulation in cancer” and “Metabolic” pathways. We also performed a comparative transcriptomic study between GCRV-infected rare minnow and grass carp data. This revealed that “IL-17 signaling pathway”, “NF-kappa B signaling pathway” and “Influenza A” pathways are conserved (important) in the regulation of anti-GCRV infection in both species, and need to be further investigated. Furthermore, a total of four immune-related DEGs were selected for qRT-PCR validation, and the results confirmed the RNA-seq data. These results enhance our understanding of the antiviral responses of cyprinid fish infected by GCRV.

Oxygen Depletion Affects Kinematics and Shoaling Cohesion of Cyprinid Fish

Numerous anthropogenic stressors impact rivers worldwide. Hypoxia, resulting from organic waste releases and eutrophication, occurs very commonly in Mediterranean rivers. Nonetheless, little is known about the effects of deoxygenation on the behavior of Mediterranean freshwater fish. To fill this knowledge gap, we assessed the impact of three different dissolved oxygen levels (normoxia, 48.4%, 16.5% saturation) on kinematics indicators (swimming velocity, acceleration, distance traveled) and shoaling cohesion of adult Iberian barbel, Luciobarbus bocagei, a widespread cyprinid species inhabiting a broad range of lotic and lentic habitats. We conducted flume experiments and video-tracked individual swimming movements of shoals of five fish. Our results reveal significant differences between the treatments regarding kinematics. Swimming velocity, acceleration, and total distance traveled decreased stepwise from the control to each of the two oxygen depletion treatments, whereby the difference between the control and both depletion levels was significant, respectively, but not between the depletion levels themselves. Shoaling cohesion showed dissimilarities between the treatments regarding the maximum distance between fish, as the high depletion treatment differed from each of the other two, indicating that under severe oxygen depletion some individuals move away from the shoal. Overall, our results show how oxygen depletion changes fish behavior, which may entail ecological responses, highlighting the need to maintain an unfragmented river network to ensure movement dispersal among habitats, thus providing conditions for species escapement from hypoxia.

Biofloc formation improves water quality and fish yield in a freshwater pond aquaculture system

High-throughput sequencing of the 16S rRNA gene of microbial communities was used to investigate how biofloc technology (BFT) improved water quality and fish yield in freshwater pond aquaculture. Three treatments included conventional treatment (CT), biofloc treatment (BT) and biofloc systems augmented with floc-forming bacterium (Zoogloea resiniphila MMB) treatment (BZT). The feeding trial lasted for 8 weeks with triplicate groups of cyprinid species in nine enclosures, which were placed in an outdoor pond to simulate a real aquaculture environment. Biofloc was generated by adding organic carbon and continuous aeration, which resulted in reducing dissolved nitrogen from 22% to 14% and sedimentary nitrogen from 49% to 5% and increasing nitrogen accumulation in biofloc and fish biomass. Nitrogen content in fish biomass increased from 28% in a CT to 42% when BFT was applied. Changes in the bacterial community and stimulation of biofloc formation played a central part in transferring nitrogen from remaining food, excreta and feces to bacteria and fish biomass. Z. resiniphila MMB did not outcompete indigenous communities and had no impact on floc formation by direct addition to the pond. Filamentous bacteria comprised the major structure of biofloc, while the proportion of zoogloea-forming microorganisms was very low. The proportion of aerobic heterotrophic microorganisms increased in both BFT treatments. Actinobacteria promoted the formation of floc and could have secondary benefits of protecting against fish pathogens, such as Aeromonas sp., though may increase the accumulation of off-flavor in the water and fish tissue.

First detection of spring viraemia of carp virus in common carp (Cyprinus carpio L.) affected by a septicaemic disease in Mexico.

Spring viraemia of carp (SVC) is an infectious disease responsible for severe economic losses for various cyprinid species, particularly common carp (Cyprinus carpio carpio). The causative agent is the SVC virus (SVCV), a member of the Sprivivirus genus, Rhabdoviridae family, and a List 1 pathogen notifiable by the World Organization for Animal Health. This study describes the diagnosis of an SVCV pathogen isolated in October 2015 from wild common carp inhabiting a natural lagoon in central Mexico. While neither an epidemic nor fish mortalities were reported, the collected killed specimens exhibited clinical signs of disease (e.g., exopthalmia, moderate abdominal distension and haemorrhaging, as well as internal haemorrhages and adhesions). Histological results of injuries were consistent with the pathology caused by SVCV. This finding was supported by the isolation of a virus in EPC and BF‐2 cells and subsequent RT‐PCR confirmation of SVCV. The phylogenetic analyses of partial SVCV glycoprotein gene sequences classified the isolates into the Ia genogroup. These findings make this the first report of SVCV detection in Mexico, extending the southern geographical range of SVCV within North America. However, since this pathogen was detected in fish inhabiting a natural body of water without tributaries or effluents, it is difficult to estimate the risk of SVCV for other wild/feral cohabitating cyprinid species in the lagoon. The status of this virus is also unknown for other bodies of water within this region.

Mechanisms for Temperature Modulation of Feeding in Goldfish and Implications on Seasonal Changes in Feeding Behavior and Food Intake.

In fish models, seasonal change in feeding is under the influence of water temperature. However, the effects of temperature on appetite control can vary among fish species and the mechanisms involved have not been fully characterized. Using goldfish (Carassius auratus) as a model, seasonal changes in feeding behavior and food intake were examined in cyprinid species. In our study, foraging activity and food consumption in goldfish were found to be reduced with positive correlation to the gradual drop in water temperature occurring during the transition from summer (28.4 ± 2.2°C) to winter (15.1 ± 2.6°C). In goldfish with a 4-week acclimation at 28°C, their foraging activity and food consumption were notably higher than their counterparts with similar acclimation at 15°C. When compared to the group at 28°C during summer, the attenuation in feeding responses at 15°C during the winter also occurred with parallel rises of leptin I and II mRNA levels in the liver. Meanwhile, a drop in orexin mRNA along with concurrent elevations of CCK, MCH, POMC, CART, and leptin receptor (LepR) transcript expression could be noted in brain areas involved in feeding control. In short-term study, goldfish acclimated at 28°C were exposed to 15°C for 24 h and the treatment was effective in reducing foraging activity and food intake. The opposite was true in reciprocal experiment with a rise in water temperature to 28°C for goldfish acclimated at 15°C. In parallel time-course study with lowering of water temperature from 28 to 15°C, short-term exposure (6–12 h) of goldfish to 15°C could also increase leptin I and II mRNA levels in the liver. Similar to our seasonality study, transcript level of orexin was reduced along with up-regulation of CCK, MCH, POMC, CART, and LepR gene expression in different brain areas. Our results, as a whole, suggest that temperature-driven regulation of leptin output from the liver in conjunction with parallel modulations of orexigenic/anorexigenic signals and leptin responsiveness in the brain may contribute to the seasonal changes of feeding behavior and food intake observed in goldfish.