Freshwater Fish Aquaculture Research Articles

Investigating transcriptomics and metabolomics differences offers insights into the mechanisms of muscular fat deposition in common carp (Cyprinus carpio)

With the global population increasing and lifestyle improving, the demand for high-quality nutritional aquatic foods has been rising. Muscle fat is a crucial nutritional index for evaluating the quality of fish flesh. However, the comprehensive and systematic understanding of the molecular mechanism underlying differences in muscle fat deposition remains insufficient. In this study, we integrated transcriptomics and metabolomics of selected samples with extremely high and low muscle fat in common carp (Cyprinus carpio), the major freshwater aquaculture fish in Asia, to identify critical genes, metabolites and metabolic pathways. We totally identified 204 differentially expressed genes (DEGs) and 1528 differentially accumulated metabolites (DAMs). Glycerolipid, glycerophospholipid and glyoxylate and dicarboxylate metabolisms were enriched through both transcriptomics and metabolomics. These lipid metabolism pathways may be regulated by some critical signal transduction pathways, including Extracellular matrix [ECM]-receptor interaction, mTOR signaling pathway and FoxO signaling pathway. Combined with the validation of gene expression and biochemical indices, a supposed regulatory network was established. To our knowledge, it is the first study to apply a multi-omics approach in fish with naturally different muscle fat to comprehensively elucidate the mechanism. This study could deepen our understanding of the molecular mechanism of muscle fat deposition and be helpful for improving the quality of fish.

Application Of Microbubble Technology To Increase Oxygen Content In The Aquaculture Of Tambaqui (Colossoma Macropomum)

The oxygen consumed is used to oxidize food substances to produce energy. Therefore, the metabolic rate is usually indicated by the rate of oxygen consumption per time unit. In most intensive aquaculture systems, oxygen content is widely used due to the high stocking density and maximum feeding rates. This study aimed to evaluate the growth performance of freshwater pomfret (Colossoma macropomum) treated with increased oxygen in two different systems. The study was conducted in a laboratory scale by applying T-test data analysis. The difference of treatment level applied in the comparison of aeration and microbubble consists of two treatments and three replications. The researcher used commercial floating pellets PF0 with 25% protein content, the feeding rate was 5% of the biomass. The feed was given daily during the culture for two times a day. Data of the study were analyzed using T-test on the Statistical Product and Service Solutions (SPSS) software Version 17.0. Results of the study showed that aeration system using microbubble resulted in dissolved oxygen (DO) of 6.5 ± 0.17, 100% pomfret fish survival rate (SR), Survival Growth Rate (SGR) of 1.83 ± 0.24, Feed Conversion Ratio (FCR) of 1.37 ± 0.17, Protein Efficiency Ratio (PER) of 2.79 ± 0.37, Feed Utilization Efficiency (FUE) of 0.67 ± 0.09, Absolute Weight Growth of 52.02 ± 1.60; it was better than using aeration. This study has developed a model of freshwater pomfret fish aquaculture to provide growth value.

Whole-genome re-sequencing reveals genetic structure and selection signals of different populations in Megalobrama amblycephala

Characterization of genetic variants is crucial for understanding the molecular mechanisms behind selected traits and enhancing the rate of genetic gain through artificial selection. This study explored the genetic diversity and population structure of blunt snout bream Megalobrama amblycephala, a key freshwater fish in Chinese aquaculture. We conducted whole-genome re-sequencing of individuals from six populations, comprising three natural and three genetically improved strains, to assess genetic diversity, population structure and the impacts of selective breeding. We identified 17,009,590 high-quality biallelic single nucleotide polymorphism (SNP) loci. Genetic diversity assessments revealed low levels of polymorphism across populations, with genetically improved strains showing moderate to high genetic differentiation from their source populations. The study also highlighted runs of homozygosity (ROH) and analyzed linkage disequilibrium (LD) decay, indicating minimal recent inbreeding and diverse recombination events among populations. Selective sweep analyses uncovered significant selection loci associated with growth and hypoxia tolerance traits. Enrichment analyses identified genes involved in olfactory signal transduction, immune response, and metabolism pathways, which are closely related to these selective traits. These findings offer insights into the genetic basis of critical traits in M. amblycephala, contributing to the conservation of germplasm resources and supporting ongoing selective breeding efforts.

Identification of body coloration related genes in ricefield eel (Monopterus albus) using GWAS

Body color is one of the most diverse external morphological characteristics of fish. It not only affects the function of fish predation and individual communication but also has important economic value. The ricefield eel (Monopterus albus) is a popular freshwater aquaculture fish species in China. Few studies have suggested some candidate genes involved in the formation of body color in this fish; however, further genetic evidences are required. Genome-wide association analysis (GWAS) is a powerful analytical method for identifying relationships between target traits and genetic markers or candidate genes in natural populations. In this study, two populations of ricefield eel with different body coloration were used to study the genetic factors that regulate the formation of body color. Through GWAS, 67 SNPs, 463 genes and 5 signaling pathways were found to be associated with body color. These results suggest that a complex molecular regulatory mechanism regulates ricefield eel body coloration. Our findings lay the foundation for subsequent genome selection breeding of ricefield eel.

Evolution and Prospects of Freshwater Fish Species and Aquaculture in Colombia: A Historical Perspective

Since the 1970s Colombia has been aware of the importance of aquaculture and inland fisheries in the future of its economy due to the constant increase of a population that is increasingly in need of protein of animal origin. In 1972, a joint project between the Government of Colombia and the Food and Agriculture Organization of the United Nations was approved and aimed at studying inland fishing and developing aquaculture in the country. The work of the project is described, as are the fish culture and fisheries research activities starting with the situation in the 1970s but comparing it with recent findings. A list of the main capture and culture fish species is given. Colombian fishing production has had great variations, but first inland water fishing was more important than marine. For instance, in 1972 total fish catch was 104,390 tons and 79% of that originated from inland waters. After the continental fisheries went down, the marine fisheries accounted in 2019 already 78 per cent of the total catch of the country. Mean standing fish crop estimates in 1975‒76 from the bay, open water and vegetation habitats in four floodplain lakes were 118, 12 and 251 kg/ha indicating clearly that the fish productivity on the Magdalena floodplain was relatively low. The aquaculture sector has been growing rapidly, reflecting global trends, and producing more than capture fisheries. Aquaculture produced 88,000 tons in 2013, which was a three-fold increase from the mid-1990s. Again twofold increase took place before 2020 when the production was almost 180,000 tons. Future development prospects of inland fisheries and aquaculture are discussed and a mention is made of the present situation of ornamental fish cultivation and trade in Colombia.

Induction of diploid gynogenesis in Micropterus salmoides using irradiated heterogeneous sperm from Siniperca chuatsi

The artificial induction of gynogenesis in fish breeding can be used to produce monosex populations. Micropterus salmoides (largemouth bass) is an important freshwater aquaculture fish, and the females grow faster than the males. In this study, we aimed to determine the best way to artificially induce largemouth bass spawning and identify suitable heterologous sperm donors to induce gynogenetic largemouth bass by suppressing extrusion of the second polar body in fertilized eggs. With respect to the artificial induction of spawning in LB, four groups were tested for hormone types. The results showed that a single intramuscular injection of the hormone combination HCG (2000 IU/kg) + LHRH-A2 (20 μg/kg) + DOM (5 mg/kg) into female largemouth bass could yield desirable spawning results, and the mean number of eggs per female in kg was 28,780 ± 4574. With respect to suitable sperm donors, largemouth bass eggs were fertilized with sperm from five fish species, and it was found that mandarin fish (Siniperca Chuatsi) sperm can activate the development of largemouth bass eggs, but most of the embryos died during development, which indicated that mandarin fish are the potential of suitable heterologous sperm donors for gynogenetic experiments with largemouth bass. The suitable optimal induction conditions were detected for chromosome doubling. The results indicated that the most effective method for promoting gynogenesis in largemouth bass was to expose inseminated eggs to a temperature of 3 °C for 15 min, beginning 2 min after fertilization. In addition, the DNA content, karyotype and morphological characteristics of the gynogenetic offspring were consistent with those of the largemouth bass. Examination of sex-specific markers and artificial propagation of the gynogenetic largemouth bass revealed that all the tested fishes were female, indicating female homogamety (XX) in the largemouth bass. In summary, in this study, we established an improved artificial spawning technique for largemouth bass and successfully induced diploid gynogenetic largemouth bass using irradiated heterogeneous sperm from mandarin fish. Our study lays a foundation for the mono-sex breeding of largemouth bass.

Biocontrol of multidrug resistant pathogens isolated from fish farms using silver nanoparticles combined with hydrogen peroxide insight to its modulatory effect

This study was divided into two parts. The first part involved the isolation, and detection of the prevalence and antimicrobial resistance profile of Aeromonas hydrophila, Pseudomonas aeruginosa, and Vibrio species from Nile tilapia fish and marine aquatic water. One hundred freshly dead Nile tilapia fish were collected from freshwater aquaculture fish farms located in Al-Abbassah district, Sharkia Governorate, and 100 samples of marine aquatic water were collected from fish farms in Port Said. The second part of the study focused on determining the in vitro inhibitory effect of dual-combination of AgNPs-H2O2 on bacterial growth and its down regulatory effect on crucial virulence factors using RT-PCR. The highest levels of A. hydrophila and P. aeruginosa were detected in 43%, and 34% of Nile tilapia fish samples, respectively. Meanwhile, the highest level of Vibrio species was found in 37% of marine water samples. Additionally, most of the isolated A. hydrophila, P. aeruginosa and Vibrio species exhibited a multi-drug resistance profile. The MIC and MBC results indicated a bactericidal effect of AgNPs-H2O2. Furthermore, a transcriptional modulation effect of AgNPs-H2O2 on the virulence-associated genes resulted in a significant down-regulation of aerA, exoU, and trh genes in A. hydrophila, P. aeruginosa, and Vibrio spp., respectively. The findings of this study suggest the effectiveness of AgNPs-H2O2 against drug resistant pathogens related to aquaculture.

Assessment and Assay Comparison for Detection of Antimicrobial Residues in Freshwater Aquaculture Fish in Erbil Governorate, Iraq.

The excessive and uncontrolled application of antibiotics in the fish farming industry, coupled with a lack of health monitoring and medication practices, is a driving force behind the escalating development of antimicrobial resistance. The present study assessed and compared qualitative field diffusion (QFD) and disk diffusion (DD) assays for the detection of antimicrobial residues (ARs) in diverse freshwater aquaculture fish. A total of 380 freshwater aquaculture fish (160 fresh and 180 frozen) samples were systematically collected between January and June 2021 from various retail stores located in Erbil Governorate, Iraq. Based on QFDA results, overall, ARs were detected (52; 15.3%) at a relatively lower frequency with comparatively higher frequency (21; 31.1%) in fresh than (31; 17.2%) frozen fish samples. On the other hand, DDA also revealed a comparable (45; 13.2%) prevalence rate of ARs. However, a low detection was observed more in fresh (17; 10.6%) than frozen (28; 15.6%) fish samples. Moreover, no statistically significant disparity (χ2 = 0.069; p = 0.79) between two assays and types of fish was recorded. In conclusion, the results of the present study showed that detecting a considerable frequency of ARs in these fish samples raises concerns about potential threats to public health. This underscores the necessity for understanding antibiotic application in aquaculture and its potential connection to antibiotic resistance in bacterial pathogens. Such comprehension is pivotal for formulating and implementing effective control and farm management strategies to address this pressing issue.

Price volatility characteristics and policy implications of freshwater fish in China

The fisheries industry in China is experiencing rapid growth, but it is also encountering the challenge of frequent fluctuations in aquatic product prices. Freshwater fish aquaculture plays a crucial role in China’s fisheries industry. Analyzing the characteristics of price volatility in freshwater fish is crucial to ensure a stable supply of aquatic products and promote sustainable fisheries industry development. This study focuses on four freshwater fish species, namely crucian carp, grass carp, silver carp, and carp, to analyze the price volatility characteristics of freshwater fish in China from 2006 to 2022. The study uses the price decomposition method and the ARCH model. The results indicate that, from the perspective of dominant characteristics of price volatility, the prices of freshwater fish display periodic volatility with an overall upward trend, as well as significant seasonal and random variations. From the perspective of recessive price volatility characteristics, the price volatility of freshwater fish exhibits clustering and asymmetry. This indicates that the price volatility of freshwater fish is influenced by previous price volatility. Positive news has a greater impact on the price volatility of freshwater fish than negative news. Out of the four freshwater fish species, only the price of crucian carp is characterized by high-risk and high-return volatility.

Antibacterial mechanism of lactobionic acid against Aeromonas salmonicida by transcriptomic analysis and its application in refrigerated grass carp

Aeromonas salmonicida is ubiquitously distributed in aquatic environments and is one of the major pathogens of freshwater aquaculture fish. Recent studies have demonstrated that A. salmonicida plays a crucial role in fish spoilage. In this study, a novel antibacterial agent, lactobionic acid (LBA), was investigated for its antibacterial effect against A. salmonicida. The results showed that the minimum inhibitory concentration (MIC) of LBA was 16 mg/mL. Bacterial cells dropped below the detection limit within 2 h after exposure to 2 MIC of LBA. The cells treated with LBA became rough and sunken, and LBA caused cellular protein leakage and an increase in conductivity. Transcriptomic analysis exhibited that the expression of 1273 genes in A. salmonicida was altered by LBA, including 700 down-regulated and 573 up-regulated genes. The most representative down-regulated genes were enriched in bacterial chemotaxis, two-component system and ATP-binding cassette transporter pathways. LBA showed an effective inhibitory effect on A. salmonicida in refrigerated grass carp and could prolong the storage time of grass carp. Overall, the intervention of LBA resulted in the decrease of cell chemotaxis and disturbance of cellular metabolic processes, which inhibited A. salmonicida. These results revealed the antibacterial mechanism of LBA against A. salmonicida, which provided a strategy for the control of fish spoilage.

Comparison of muscle nutritional composition, texture quality, carotenoid metabolites and transcriptome to underling muscle quality difference between wild-caught and pond-cultured Yellow River carp (Cyprinus carpio haematopterus)

The common carp is one of the most important freshwater aquaculture fish. The quality is an emerging concern for aquatic animals, and wild-caught fish is considered to exhibit better quality compared with cultured fish in some species. In present study, muscle nutritional composition, flesh quality index, scale and fins color, carotenoid metabolites, and RNA-sequencing were compared between wild-caught carp (WCC) and pond-cultured carp (PCC) to elucidate their quality difference. Results showed that WCC showed higher moisture, EPA, DHA, and EAA/TAA compared with PCC (P < 0.05). However, PCC showed higher muscle protein and lipid content, and mono-unsaturated fatty acids (MUFA). Hardness, chewiness, and shear force were significantly higher in WCC compared with PCC. The WCC showed higher a* and b*values in back and caudal fin (P < 0.05). Targeted metabolomics of carotenoids analysis showed that 4 carotenoid metabolites in scale and 6 carotenoid metabolites in fins showed significant difference between WCC and PCC. Furthermore, transcriptome analysis showed that a total of 8624 differentially expressed genes (DEGs) were identified in WCC vs. PCC. Gene function enrichment demonstrated that up-regulated DEGs were mainly in response to cell cycle, immunology regulation, and inositol phosphates metabolism, whereas, down-regulation genes were mainly in response in RNA transport, carbohydrate metabolism, protein and lipid metabolism. The study provided a comprehensive view of nutritional and texture difference between WCC and PCC, and which could provide reference for improving nutritional and texture quality in farmed carp.

The Assessment of Freshwater Quality in the Sungai Semantan Based on the Malaysian‘s Index of Freshwater Quality

Sungai Semantan is important for fish aquaculture industry in Malaysia. Therefore, the aimed of this article is to assess the index of freshwater quality (WQI) of the Sungai Semantan, Pahang during the rainy season (February to April 2018). The Sungai Semantan WQI was monitored at three stations by assessing six freshwater quality parameters, i.e., DO, BOD, COD, NH3-N, pH, and TSS. The Semantan River’s WQI was assessed using the Malaysian Department of Environment’s WQI classification. The results showed that three freshwater quality parameters, namely DO (6.32 mg/l), COD (46.8 mg/l), and TSS (104.4 mg/l), exceeded the standard at certain stations and classified as Class IV. However, on average, all parameters showed Classes I to III for all stations, and WQI indicated the Semantan River was slightly polluted (WQI 78.2), and classified as Class II. Changes in land use in the Temerloh district for agricultural and urbanisation have exacerbated the Semantan River’s WQI. Contradict to perception that the aquaculture is the main source of freshwater pollution for the Semantan River. Consequently, the Semantan River’s WQI must be monitored regularly, as the river is critical not only for domestic freshwater supply but also for freshwater fish aquaculture and ecotourism.

Estimating SVCV waterborne transmission and predicting experimental epidemic development: A modeling study using a machine learning approach

Viral infectious diseases significantly threaten the sustainability of freshwater fish aquaculture. The lack of studies on epidemic transmission patterns and mechanisms inhibits the development of containment strategies from the viewpoint of veterinary public health. This study raises an epidemic mathematical model considering water transmission with the aim of analyzing the transmission process more accurately. The basic reproduction number R0 was derived by the model parameter including the water transmission coefficient and was used for the analysis of the virus transmission. Spring viremia of carp virus (SVCV) and zebrafish were used as model viruses and animals, respectively, to conduct the transmission experiment. Transmission through water was achieved by connecting two aquarium tanks with a water channel but blocking the fish movement between the tanks. With the collected experimental data, we determined the optimal hybrid machine learning algorithm to analyze the transmission process using an established mathematical model. In addition, future transmission was predicted and validated using the epidemic model and an optimal algorithm. Finally, the sensitivity of model parameters and the simulations of R0 variation were performed based on the modified complex epidemic model. This study is of significance in providing theoretical guidance for minimizing R0 by manipulating model parameters with containment measures. More importantly, since the modified model and algorithm demonstrated better performance in handling freshwater fish transmission problems, this study advances the future application of transmissible disease modeling with larger datasets in freshwater fish aquaculture.

Infection dynamic of Micropterus salmoides rhabdovirus and response analysis of largemouth bass after immersion infection.

Largemouth bass (Micropterus salmoides) is an important economic freshwater aquaculture fish originating from North America. However, the frequent outbreaks of Micropterus salmoides rhabdovirus (MSRV) have seriously limited the healthy development of Micropterus salmoides farming industry. In the present study, a strain of MSRV was isolated and identified from infected largemouth bass by PCR, transmission electron micrograph observation and genome sequences analysis, and tentatively named MSRV-HZ01 strain. Phylogenetic analyses showed that the MSRV-HZ01 presented the highest similarity to MSRV-2021, followed by MSRV-FJ985 and MSRV-YH01. The various tissues of juvenile largemouth bass exhibited significant pathological damage following MSRV-HZ01 immersion infection, and the mortality reached 90%. We also found that intestine was the key organ for MSRV to enter the fish body initially by dynamic analysis of viral infection, and the head kidney was the susceptible tissue of virus. Moreover, the MSRV was also transferred to the external mucosal tissue in later stage of viral infection to achieve horizontal transmission. In addition, the genes of IFN γ and IFN I-C were significantly up-regulated after MSRV infection to exert antiviral functions. The genes of cGAS and Sting might play an important role in the regulation of interferon expression. In conclusion, we investigated the virus infection dynamics and fish response following MSRV immersion infection, which would promote our understanding of the interaction between MSRV and largemouth bass under natural infection.

Isolation and pathogenicity evaluation of Escherichia coli O157:H7 from common carp, Cyprinus carpio

Escherichia coli O157:H7 is the primary serotype of enterohaemorrhagic E. coli (EHEC), which can cause diarrhea, hemorrhagic colitis, and hemolytic uremic syndrome. It is considered as a major health concern due to it being a zoonotic disease that is transmitted through food. In this study, a pathogenic bacterium was isolated from infected carp, which identified as E. coli O157:H7 named X21 through genetic sequencing, phylogenetic analysis, physiological and biochemical tests. In the experiment, crucian carp was used as a model to study the pathogenicity of the isolate, the pathological histological observations and cytokines expression of fish tissues were determined after bacterial challenge. The results showed that severe pathological damage observed in the liver, spleen, headkidney of fish infected with isolate X21. Besides, we found that accumulation of IgT+ B cells in the lamina propria of intestine, and up-regulation of SUCH-r, IL-1β, IL-10, IL-11, MyD88, and TNF-α gene in various tissues. After challenged, the survivability of crucian carp infected with isolate X21 stands at a mere 14.27%. To our knowledge, this is the first report that E. coli O157:H7 infected the freshwater fish C. carpio, which indicates that this bacterium is a potential threat to public health and freshwater fish aquaculture.

The Present Situation of the Fisheries Sector in Iraq: A Critical Review

In this review, the status of fisheries in Iraq is described. Iraq has two main water resources, the Tigris and Euphrates Rivers, forming a water area of approximately 700,000 hectares. Surface waters are distributed as natural lakes (39%), dam lakes (13.3%), and rivers and their tributaries (3.7%). On the other hand, marshes constitute 44% of the water sources in Iraq. The Iraqi government began recording fish production from wild and aquaculture in 1986. Total fish production from freshwaters in Iraq in 1991 and 1998 were 18,800 and 30,000 tons, respectively. In 2020, the total fish production in Iraq reached to 241,848 tons (Anonymous, 2022a). The bulk of fish production belonged to carps followed by barbs (genus Barbus) and trouts. With respect to capture fishing in Iraq, a variety of trawl nets (single-bag and multi-bag) and gillnets have commonly been used. The 1970s and 1980s were characterized by low consumption of fish meat (i.e., 4.3 kg in 1979), but it has gradually increased over the last years and has reached a remarkable 10 kg per capita in 2020. In this review, freshwater and marine fish species, aquaculture production and wild catch, institutions and centers specialized in researching and developing fisheries, fish meat consumption, problems of the fishing industry and potential solutions to develop the fishing industry in Iraq are outlined. This is the first study on the present status of fisheries in Iraq.

Characteristics and expression profiles of MHC class Ⅰ molecules in Carassius auratus.

Major histocompatibility complex class Ⅰ (MHC Ⅰ) molecules play a vital role in adaptive immune systems in vertebrates by presenting antigens to effector T cells. Understanding the expression profiling of MHC Ⅰ molecules in fish is essential for improving our knowledge of the relationship between microbial infection and adaptive immunity. In this study, we conducted a comprehensive analysis of MHC Ⅰ gene characteristics in Carassius auratus, an important freshwater aquaculture fish in China that is susceptible to Cyprinid herpesvirus 2 (CyHV-2) infection. We identified approximately 20 MHC Ⅰ genes discussed, including U, Z, and L lineage genes. However, only U and Z lineage proteins were identified in the kidney of Carassius auratus using high pH reversed-phase chromatography and mass spectrometry. The L lineage proteins were either not expressed or present at an extremely low level in the kidneys of Carassius auratus. We also used targeted proteomics to analyze changes in protein MHC Ⅰ molecules abundance in healthy and CyHV-2-infected Carassius auratus. We observed that five MHC Ⅰ molecules were upregulated, and Caau-UFA was downregulated in the diseased group. This study is the first to reveal the expression of MHC Ⅰ molecules at a large scale in Cyprinids, which enhances our understanding of fish adaptive immune systems.

The environmental impact and development direction of grass carp, Ctenopharyngodon idella, aquaculture

AbstractGrass carp, Ctenopharyngodon idella, is the largest freshwater aquaculture fish species worldwide. However, its environmental impacts are increasingly controversial. In this paper, we considered the production of a 1500 g commercial grass carp as an example, analyzed through a life cycle assessment. The results showed that the indicators of global warming potential (GWP), acidification potential, eutrophication potential, freshwater eco‐toxicity potential (FAETP), land competition (LC), and fossil energy consumption of producing 1 kg of grass carp were equivalent to 5.7267 kg of CO2, 0.0648 kg of 1,4‐DCB0, 0.0010 kg of P, 0.0276 kg of SO2, 8.2951 m2, 0.3491 kg of oil, respectively, and were mainly from feed processing and water pollution. Compared with pig, beef, and sheep production, grass carp production has lower environmental impacts, but in terms of GWP, FAETP, and LC were significantly higher than chicken production, especially water pollution and discharge, which is an important consideration. This study clarifies the direction of grass carp production and key focus areas include producing low carbon and nitrogen emission feed, application of ecological engineering aquaculture system, intelligent mechanization technology and equipment.

The myxozoan parasite Myxobolus bejeranoi (Cnidaria: Myxozoa) infection dynamics and host specificity in hybrid tilapia aquaculture.

Nile × blue tilapia hybrid (Oreochromis niloticus × O. aureus) has become an important food fish in intensive freshwater aquaculture. Recently, the parasite Myxobolus bejeranoi (Cnidaria: Myxozoa) was found to infect hybrid tilapia gills at high prevalence, causing immune suppression and high mortality. Here, we explored additional characteristics of M. bejeranoi–tilapia interaction, which enable efficient proliferation of this parasite inside its specific host. Highly sensitive quantitative polymerase chain reaction (qPCR) and in situ hybridization analyses of fry collected from fertilization ponds provided evidence to an early-life infection of fish by a myxozoan parasite, occurring less than 3 weeks post-fertilization. Because Myxobolus species are highly host-specific, we next compared infection rates in hybrid tilapia and in both its parental species following a 1-week exposure to infectious pond water. Analysis by qPCR and histological sections showed that while blue tilapia was as susceptible to M. bejeranoi as the hybrid, Nile tilapia appeared to be resistant. This is the first report of differential susceptibility of a hybrid fish vs its parental purebreds to a myxozoan parasite. These findings advance our understanding of the relationship between M. bejeranoi and tilapia fish and raise important questions regarding the mechanisms that allow the parasite to distinguish between very closely related species and to infect a specific organ at very early-life stages.

Marketing Channels of Freshwater Aquaculture Fish in the Red River Delta of Vietnam: A Case Study in Hai Duong Province

Freshwater aquaculture has played key roles in the livelihood development of farm households in the Red River Delta through freshwater fish ponds, rice-and-fish, and marine cage culture. A market-driven approach is being addressed more and more in promoting new production. This study aimed to analyze the marketing channels of freshwater aquaculture fish in Hai Duong province. The study was conducted with 151 farm households belonging to three fish production system: Fish system engaging fish production only (FS); animal fish system combining animal and fish production (AF) ; and new garden-pond-animal house system (VAC) in the province. The attained results reveal that fish farmers diversified their marketing strategies to obtain a marketing margin of about 87% of the retail price of the finfish along with their value distribution while the remaining portion of the marketing margins belonged to the intermediary market actors. The cost of the purchased fish commodities accounts for the majority of the total cost for all actors. The cost of dead fish presented the highest proportion of the total marketing cost. A large portion of the marketing costs represented wages, fuel, and the rent of a business place. The marketing margin for the intermediary stakeholders in both the studied channels was 12.7%, in which marketing costs accounted for approximately 5.0%. The results will be used for designing better promotion strategies for freshwater fish production and providing good lessons for small-scale fresh aquaculture development towards livelihood diversification and development in rural areas.