High-density Aquaculture Research Articles

Chronic hypoxia drives the occurrence of ferroptosis in liver of fat greening (Hexagrammos otakii) by activating HIF-1α and promoting iron production

BackgroundHypoxia caused by global climate change and human activities has become a growing concern eliciting serious effect and damages to aquatic animals. Hexagrammos otakii is usually a victim of hypoxia which caused by high density aquaculture and high nutrient input. The mechanism underlying ferroptosis regulation after hypoxia-stress in liver of H. otakii, however, remains elusive. MethodsFor a duration of 15 days, expose the H. otakii to low concentrations of dissolved oxygen (3.4 ± 0.2 mg/L). Detecting alterations in the H. otakii liver tissue by chemical staining, immunohistochemistry, and electron microscopy. The expression variations of relevant genes in the liver of the H. otakii were simultaneously detected using Western blot and qPCR. A correlation analysis was performed between HIF-1α and iron ion expression in the liver of H. otakii following hypoxic stress. ResultsIn this study, we conducted the whole ferroptosis integrated analysis of H. otakii under chronic hypoxic condition. Reactive oxygen species (ROS) are highly accumulated under the hypoxia treatment (Superoxide Dismutase, SOD; Catalase, CAT), and which results in a significantly enhanced of lipid peroxidation (Lipid Peroxidation, LPO; Malondialdehyde, MDA; Aminotransferase, AST; Alanine aminotransferase, ALT) in liver tissue. The HIF-1α signaling is activated to cope with the hypoxia stress through strategies including changing iron ion concentration (Fe3+ and TFR1) to breaking the oxidation balance (GSH and GSH-Px), and enhancing ferroptosis gene expression (GPX4). The expression of genes related to ferroptosis pathway (DMT1, FTH1, STEAP3, ACSL4, γ-GCS, SLC7A11) is significantly upregulated and associated to the expression of iron and HIF-1α. ConclusionsIt is demonstrated that the HIF-1α/Fe3+/ROS/GPX4 axis is involved in promoting ferroptosis in fat greening hepatocytes following hypoxia-stress. Ultimately, our findings unveil a process by which hypoxic stress strongly encourages ferroptosis by triggering HIF-1α and boosting iron synthesis.

Response signatures of intestinal microbiota and gene transcription of yellow catfish (Pelteobagrus fulvidraco) to Aeromonas hydrophila infection

Bacterial intestinal inflammation is a common disease of yellow catfish (Pelteobagrus fulvidraco) in high-density aquaculture. Understanding the interactions between host and intestinal bacteria is helpful to intestinal inflammatory disease control. Here, we constructed a model of intestinal inflammation after Aeromonas hydrophila infection in yellow catfish, and characterized variations in gene expression and microbiome in the gut through high-throughput sequencing. Furthermore, host gene-microbiome interactions were identified. Histology observation showed disordered distribution of columnar epithelial cells and decrease of goblet cells in intestine. A total of 4741 genes showed differentially expression, mostly in comparisons between 12 hpi group with each other groups respectively, including control, 24 hpi and 48 hpi groups. These genes were enriched in immune-related pathways including the IL-17 signaling pathway, triggering strong inflammatory response at the invading stage within 12 h. Subsequently, the host strengthened energy consumption by activating carbohydrate and lipid metabolism pathways to repair the intestinal mucosal immune defense line. In addition, fish with A. hydrophila infection show decreased richness of gut microbial, reduced relative abundance of probiotics including Akkermansia, and elevated pathogenic bacteria such as Plesimonas. An integrative analysis identified A. hydrophila-related genes, such as il22 and stat3, for which expression level is close associated with the shift of A. hydrophila-related bacteria relative abundance, such as Akkermansia and Cetobacterium. Aside from picturing the variations of intestine gene expression and mucosal microbiome of yellow catfish coping with A. hydrophila infection, our study probed the underlying host-microbe interactions in A. hydrophila infection induced intestinal inflammatory, providing new insights for disease control in aquaculture.

Effects of stocking density on behavior, physiology, and gene expression of the sea cucumber Apostichopus japonicus

The behavioral and physiological mechanisms induced by high density remain mostly unknown in sea cucumbers, although it has been widely adopted to increase the space usage efficiency in aquaculture. The present study focused on investigating how high density affects fitness-related behaviors, physiology, and gene expression in the sea cucumber Apostichopus japonicus. We found that high density significantly increased crawling behavior of sea cucumbers in short-term (one week), while significantly inhibited feeding behavior in long-term (seven weeks). Foraging behavior was not significantly affected in sea cucumbers at high density. Our study found that short-term high density did not have a significant impact on the cortisol and glucose concentration in A. japonicus. There was no significant difference in serotonin (5-HT) of sea cucumbers between high and low density. Gamma-aminobutyric acid (GABA) significantly increased in sea cucumbers at high density. Thus, GABA probably plays a crucial role in regulating the behavior of A. japonicus at high density. In addition, we conducted a transcriptome analysis on intestinal tract of sea cucumbers at two different stocking densities. There were 117 differentially expressed genes (DEGs) were discovered, including 72 up-regulated DEGs and 45 down-regulated DEGs. Gene Ontology (GO) functional annotation revealed that the DEGs were significantly enriched in the processes of oxidation-reduction, dioxygenase activity, and oxidoreductase activity. Additionally, the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed a significant enrichment of DEGs in glycerolipid metabolism and PPAR signaling pathways. We highlighted LPL encoding lipoprotein esterase, which probably plays an important role in lipid metabolism in A. japonicus under high density. In conclusion, the present study clarified the behavioral and physiological reactions and further revealed the related molecular mechanisms of A. japonicus in a high-density condition. This provides valuable information into the management of the high-density aquaculture of sea cucumbers.

Observation of Agonistic Behavior in Pacific White Shrimp (Litopenaeus vannamei) and Transcriptome Analysis.

Agonistic behavior has been identified as a limiting factor in the development of intensive L. vannamei aquaculture. However, the characteristics and molecular mechanisms underlying agonistic behavior in L. vannamei remain unclear. In this study, we quantified agonistic behavior through a behavioral observation system and generated a comprehensive database of eyestalk and brain ganglion tissues obtained from both aggressive and nonaggressive L. vannamei employing transcriptome analysis. The results showed that there were nine behavior patterns in L. vannamei which were correlated, and the fighting followed a specific process. Transcriptome analysis revealed 5083 differentially expressed genes (DEGs) in eyestalk and 1239 DEGs in brain ganglion between aggressive and nonaggressive L. vannamei. Moreover, these DEGs were primarily enriched in the pathways related to the energy metabolism process and signal transduction. Specifically, the phototransduction (dme04745) signaling pathway emerges as a potential key pathway for the adjustment of the L. vannamei agonistic behavior. The G protein-coupled receptor kinase 1-like (LOC113809193) was screened out as a significant candidate gene within the phototransduction pathway. Therefore, these findings contribute to an enhanced comprehension of crustacean agonistic behavior and provide a theoretical basis for the selection and breeding of L. vannamei varieties suitable for high-density aquaculture environments.

Establishment and characterization of a golden pompano (Trachinotus blochii) fin cell line for applications in marine fish pathogen immunology

Pompano fishes have been widely farmed worldwide. As a representative commercial marine species of the Carangidae family, the golden pompano (Trachinotus blochii) has gained significant popularity in China and worldwide. However, because of rapid growth and high-density aquaculture, the golden pompano has become seriously threatened by various diseases. Cell lines are the most cost-effective resource for in vitro studies and are widely used for physiological and pathological research owing to their accessibility and convenience. In this study, we established a novel immortal cell line, GPF (Golden pompano fin cells). GPF has been passaged over 69 generations for 10 months. The morphology, adhesion and extension processes of GPF were evaluated using light and electron microscopy. GPF cells were passaged every 3 days with L-15 containing 20 % fetal bovine serum (FBS) at 1:3. The optimum conditions for GPF growth were 28 °C and a 20 % FBS concentration. DNA sequencing of 18S rRNA and mitochondrial 16S rRNA confirmed that GPF was derived from the golden pompano. Chromosomal analysis revealed that the number pattern of GPF was 48 chromosomes. Transfection experiments demonstrated that GPF could be utilized to express foreign genes. Furthermore, heavy metals (Cd, Cu, and Fe) exhibited dose-dependent cytotoxicity against GPF. After polyinosinic-polycytidylic acid (poly I:C) treatment, transcription of the retinoic acid-inducible gene I-like receptor (RLR) pathway genes, including mda5, mita, tbk1, irf3, and irf7 increased, inducing the expression of interferon (IFN) and anti-viral proteins in GPF cells. In addition, lipopolysaccharide (LPS) stimulation up-regulated the expression of inflammation-related factors, including myd88, irak1, nfκb, il1β, il6, and cxcl10 expression. To the best of our knowledge, this is the first study on the immune response signaling pathways of the golden pompano using an established fin cell line. In this study, we describe a preliminary investigation of the GPF cell line immune response to poly I:C and LPS, and provide a more rapid and efficient experimental material for research on marine fish immunology.

Experimental Research on a Gas Liquid Mixing Oxygen Increasing Device based on Microbubbles

With the development of large-scale and high-density aquaculture, higher requirements have been put forward for the effectiveness of water oxygenation. In response to the problems of low oxygenation efficiency and high energy consumption of oxygenation devices on the market, a new type of oxygenation device was designed based on the theory of microbubble generation technology, and its oxygenation performance was studied through clear water oxygenation experiments. The experimental results show that under the action of microbubbles, the oxygenation device has the best oxygenation effect when the water flow rate and oxygen flow rate are 2.4m3/h and 0.4L/min, respectively. After adding oxygen to clean water with an initial oxygen concentration of 5.3mg/L through the device, the oxygen concentration increased to 11.2mg/L, reaching a supersaturated state. The oxygen absorption rate was 41.2%, and the oxygenation capacity was 6.68kg/h. Compared to traditional oxygenation machinery, under the premise of achieving the same oxygenation effect, the oxygenation time is shorter, effectively improving the oxygenation efficiency

Mass variations and transfer process of shrimp farming pollutants in aquaculture drainage systems: Effects of DOM features and physicochemical properties

The expansion of aquaculture produces increasing pollutant loads, necessitating the use of drainage systems to discharge wastewater into surface water. To assess the mass variations and transfer process of aquaculture wastewater, an entire aquaculture drainage investigation lasting for 48 h was conducted, focusing on the nutrients, heavy metals, dissolved organic matter (DOM), and physicochemical properties of drainage in a commercial shrimp farm. The findings revealed that early drainage produced more heavy metals, total nitrogen (TN), dissolved organic nitrogen (DON), and feed-like proteins from aquaculture floating feed and additives, whereas late drainage produced more PO43--P and total dissolved phosphorus (TP). A few pollutants, including DON, Cu, and feed-like proteins, were effectively removed, whereas the contents of TN, dissolved inorganic nitrogen, and Zn increased in the multi-level aquaculture drainage system. Limited dilution indicated that in-stream transfer was the main process shaping pollutant concentrations within the drainage system. In the lower ditches, NO3--N, heavy metals, and feed-like proteins exhibited evident in-stream attenuation, while TN and NH4+-N underwent significant in-stream enrichment processes, especially in ditch C, with the transfer coefficient values (vf) of –1.74E-5 and –2.04E-5. This indicates that traditional aquaculture drainage systems serve as nitrogen sinks, rather than efficient nutrient purge facilitators. Notably, DOM was identified as a more influential factor in shaping the in-stream transfer process in aquaculture drainage systems, with an interpretation rate 40.79% higher than that of the physiochemical properties. Consequently, it is necessary to eliminate the obstacles posed by DOM to pollutant absorption and net zero emissions in aquaculture drainage systems in the future. Environmental implicationsNutrients, heavy metals, and dissolved organic matter are hazardous pollutants originating from high-density aquaculture. As the sole conduit to natural waters, aquaculture drainage systems have pivotal functions in receiving and purifying wastewater, in which the in-stream transfer process is affected by ambient conditions. This field study investigated the spatial variations, stage distinctions, effects of physicochemical properties, and dissolved organic matter (DOM) features. This finding suggests that the aquaculture drainage system as a nitrogen sink and DOM source. While the DOM is the key factor in shaping the in-stream transfer process, and obstacles for pollutant elimination. This study helps in understanding the fate of aquaculture pollutants and reveals the drawbacks of traditional aquaculture drainage systems.

Characteristics and risk assessment of cryptocaryoniasis in large yellow croaker (Larimichthys crocea) at different densities in industrialized aquaculture

With the introduction and advancement of sustainable development in aquaculture, traditional fish farming methods are gradually transitioning to advanced industrial farming models. To explore the occurrence patterns and risks of cryptocaryoniasis in industrialized high-density aquaculture, we used a non-lethal dose of Cryptocaryon irritans theronts (400 theronts/m3) to infect Larimichthys crocea at different rearing densities [low-density group (0.088 kg/m3), medium-density group (0.88 kg/m3), and high-density group (8.80 kg/m3)]. We explored the relationship between L. crocea density and the growth rate of the C. irritans population by observing the differences in growth, feeding, and survival rates of the L.crocea in each group and the changes in water quality and the number of C. irritans tomonts during the rearing process. We also evaluated the risks associated with the occurrence of cryptocaryoniasis in aquaculture. The results showed significant differences in the relative levels of the first round of infection among different density groups of L.crocea, which affected the outbreak speed of cryptocaryoniasis and the maximum relative tomont number (RTN) of L. crocea. Specifically, the outbreak speed of cryptocaryoniasis from fast to slow was as follows: medium-density group>low-density group>high-density group. The RTN when all L.crocea had died in each group was 12.82 (medium-density group), 49.7 (low-density group), and 106.58 (high-density group). The occurrence of cryptocaryoniasis reduced the feeding and growth rates of L.crocea in all groups, and the effect was most pronounced in the second week and the late stages of infection. The occurrence of cryptocaryoniasis caused abnormal swimming behavior in all three density groups. The main manifestations of C. irritans infection in L. crocea included rubbing the snout against the barrel wall, body imbalance, dispersed swimming, and delayed responses. The deterioration of water quality was most pronounced in the high-density group, but the outbreak speed of cryptocaryoniasis was the slowest in the high-density group, suggesting that no significant correlation existed between the deterioration of water quality and the outbreak speed of cryptocaryoniasis. The outbreak speed of cryptocaryoniasis varies depending on the fish-rearing density, and the progression and risk of cryptocaryoniasis are not proportionally correlated with the rearing density of L. crocea.

Individual Fish Echo Detection Method Based on Peak Delay Estimation and Instantaneous Frequency Characterization

In fisheries science research and farmed fish monitoring, acquiring individual fish echoes is the basis for the growth assessment, tracking, and target strength estimation of farmed fish. However, individual fish echo detection methods based on narrowband signal features cannot be applied well to high-density aquaculture scenarios. The broadband signaling system can improve the distance resolution of the detected target and can help to improve the performance of individual fish echo detection. In this study, for the broadband signal system and the characteristics of the underwater fish acoustic echoes, an individual fish echo detection method is proposed using the matched filter output envelope peak interval and instantaneous frequency characteristics of the echo as evaluation indices, and the simulation and experiments of the method are carried out in an anechoic water tank. The results show that the broadband signal system and the corresponding detection method perform better in detecting single target echoes than the narrowband signal system. Compared with the broadband single echo detection method that only relies on the peak interval of the matched filter envelope, the joint detection method that incorporates the instantaneous frequency characteristics of the echo signal has a better rejection capability for overlapping echoes, which can reduce the probability of misjudging the overlapping echoes. The combined detection methods may provide a better detection performance for individual fish echoes.

A northern snakehead (Channa argus) model of intestinal inflammation induced by Aeromonas hydrophila: Construction and transcriptome analysis

Bacterial intestinal inflammation is a common disease of aquatic animal in high-density aquaculture. This study aims to construct a model of intestinal inflammation in northern snakehead, and analyze the intestinal transcriptome after Aeromonas hydrophila (A. hydrophila) infection by high-throughput sequencing technologies (RNA-seq), in order to obtain candidate genes and regulatory pathways that may participate in inflammatory response. Northern snakehead [(13.05 ± 2.39) g] were infected through anal for 24 h with different concentrations of A. hydrophila (1.0 × 10−4, 1.0 × 10−5, 1.0 × 10−6, 1.0 × 10−7 and 1.0 × 10−8 CFU/mL).Intestinal histology observation showed that infection with A. hydrophila caused obvious inflammatory responses in intestine, especially in hindgut. The results also indicated that intestinal permeability related parameters (D-LA and Na+-K+-ATP), immune-related parameters (C3, LZM, AKP, MPO, IL-1β and TNF-α) and immune-related gene expression (il-1β and tnf-α) were significantly changed compared to the CK group. In this process, high concentration of A. hydrophila infection caused the death of snakehead. On the basis of the above evaluation, we successfully constructed a model of intestinal inflammation induced by A. hydrophila in northern snakehead, and the optimal dosage of A. hydrophila was 1.0 × 10−6 CFU/mL. Subsequently, the constructed model was analyzed on the Illumina Genome Analyser II platform for intestinal transcriptome. Results showed that a total of 370,492,420 clean reads, 145,236 transcripts and 89,431 unigenes were obtained. Moreover, a total of 7566 differentially expressed genes (DEGs) were found, including 4486 upregulated genes and 3080 downregulated genes. Notably, the key pathways [Toll-like receptors (TLRs) and NOD-like receptors (NLRs)] and genes [tlr1, tlr2, tlr5, nf-κb, tnf-α, il-1β, il-10, nod1] related to inflammation were discovered. These results revealed the response of northern snakehead to A. hydrophila at the transcriptional level, which provide insights for the regulatory mechanisms of intestinal inflammation in northern snakehead.

Molecular and functional characterization of golden pompano (Trachinotus blochii) TBK1 on IFN regulation

The golden pompano (Trachinotus blochii), a pivotal commercial marine species in China, has gained significant popularity worldwide. However, accompanied with rapid growth and high density aquaculture, golden pompano has been seriously threatened by Nervous necrosis virus (NNV), while its molecular biology research regarding the innate immune system remains unexplored, which is crucial for understanding the activation of interferon (IFN) production and antiviral responses. In this study, we aimed to identify the characterization and function of golden pompano TANK-binding kinase 1 (gpTBK1), thereby providing evidence of the conservation of this classical factor in the RLR pathway among marine fish. Initially, we found the expression of gpTBK1 upregulation in diseased golden pompano with NNV infection and we successfully cloned the full-length open reading frame (ORF) of gpTBK1, consisting of 2172 nucleotides encoding 723 amino acids, from the head kidney. Subsequent analysis of the amino acid sequence revealed homology between gpTBK1 and other fish TBK1 proteins, with conserved N-terminal Serine/Threonine protein kinases catalytic domain (S_TKc) and C-terminal coiled coil domain (CCD). Moreover, the expression pattern showed that gpTBK1 exhibited ubiquitous expression across all evaluated tissues. Furthermore, functional identification experiments indicated that gpTBK1 activated interferon promoters’ activity in golden pompano and induced the expression of downstream IFN-stimulated genes (ISGs). Notably, gpTBK1 was found to co-localize and interact with gpIRF3 in the cytoplasm. Collectively, these data provide a comprehensive analysis of the characterization and functional role of gpTBK1 in promoting interferon production. This research may facilitate the further study of the innate antiviral response, particularly the anti-NNV mechanisms, in golden pompano.

Quantifying the contribution of mangroves to local fish consumption in Indonesia: a cross-sectional spatial analysis

Indonesia has lost more mangroves than any other country. The importance of mangroves for carbon storage and biodiversity is well recognised, but much less is known about what they contribute to the communities living near them who are called on to protect them. Malnutrition in Indonesia is high, with more than a third of children stunted, partly due to poor diets. Fish are nutrient-rich and are the most widely consumed animal source food in Indonesia, making the relationship between mangroves and fish consumption of great importance. Aquaculture is also tremendously important for fish production in Indonesia and has replaced large areas of mangroves over the last two decades. We performed a cross-sectional, spatial analysis in this study. We combined data on fish consumption for rural Indonesian coastal households from the Indonesian National Socioeconomic Survey with spatial data on mangrove forest and aquaculture area from the Indonesian Ministry of Environment and Forestry to create a cross-sectional spatial dataset. Using a mixed-effects regression model, we estimated to what extent living in proximity to different densities of mangroves and aquaculture was associated with fresh fish consumption for rural coastal households. Our sample included 6741 villages with 107 486 households in 2008. The results showed that rural coastal households residing near high-density mangroves consumed 28% (134/477) more fresh fish and other aquatic animals, and those residing near medium-density mangroves consumed 19% (90/477) more fresh fish and other aquatic animals, than coastal households who did not live near mangroves. Coastal households that lived near high-density aquaculture consumed 2% (9/536) more fresh fish, and those that lived near medium-density aquaculture consumed 1% (3/536) less, than other rural coastal households. Mangroves contribute substantially to the food security and nutrition of coastal communities in Indonesia. This finding means that the conservation of mangroves is important not only for carbon storage and biodiversity, but also for the communities living near them. Aquaculture does not appear to offer similar food security benefits. Bureau for Economic Growth, Education, and Environment, United States Agency for International Development.

Accumulated CO2 affects growth, acid-base regulation and ion balance of turbot (Scophthalmus maximus) in a recirculating aquaculture system

The major advantage of recirculating aquaculture systems (RAS) is the ability to manipulate and control environmental variables to optimize production efficiency. However, the characteristics of water recycling and high-density aquaculture in RAS may result in the rapid accumulation of carbon dioxide (CO2) when raising high-density marine fish. This study aimed to evaluate the effects of CO2 on growth-related parameters, tissue structure, acid-base homeostasis, and ion regulation in turbot (Scophthalmus maximus). Turbot were subjected to five different CO2 treatments (C, 8, 16, 24, and 32 mg/L) at a temperature of 14 °C for durations of 7, 15, 30, and 60 days. The results indicated a substantial reduction in specific growth rate with increasing duration of CO2 exposure, accompanied by a significant increase in feed conversion rate. Exposure to CO2 also triggered the deposition of lipids or glycogen in the turbot liver, inhibiting the expression of growth factors. Additionally, it caused dissolution of the intestinal lamina propria and vacuolation of the intestinal mucosa. Even exposure to low levels of CO2 (8 mg/L) caused damage to the turbot gill tissue. Plasma analysis of turbot showed significantly higher concentrations of plasma HCO3− and significantly lower concentrations of Na+ and Cl−. Plasma HCO3− concentrations reached a maximum of 33.35 ± 0.13 mmol/L in the 32 mg/L treatment, and genes related to osmoregulation and acid-base homeostasis in the gill (H+-ATPase, NBCI, CA, AE, NHE1, NHE2) were altered based on the duration of CO2 exposure. The kidney did not exhibit significant damage throughout the experiment, and genes related to renal osmoregulation and acid-base homeostasis (AE, NBCI, NHE3, CAII, CAIV) were significantly elevated with CO2 exposure compared to the control group. These findings indicate that prolonged exposure to CO2 has a severe impact on feeding, resulting in damage to the liver and intestinal tissues, stress within the fish body, and disrupted expression of key genes related to the growth hormone/insulin-like growth factor axis. The study highlights the significance of monitoring CO2 concentrations in RAS for optimal marine fish health, as even concentrations below the 8 mg/L threshold have an impact on turbot. The involvement of turbot kidneys strengthens their buffering capacity against CO2, but CO2 stress still affects the gut and growth axis due to ion exchange and the progression of the HCO3−buffering system, leading to growth inhibition. Overall, this study provides valuable insights into the effects of CO2 exposure on turbot aquaculture and underscores the importance of monitoring CO2 concentrations in RAS to ensure optimal health of marine fish.

Morphological change and differential proteomics analysis of gill in Mytilus coruscus under starvation.

Mytilus coruscus is a dominant shellfish in the Yangtze estuary and its adjacent sea area. Food deprivation often occurs during their growth due to fluctuations in algal abundance caused by seasonal freshwater flushing and high-density aquaculture mode. To investigate the coping strategies of M. coruscus to starvation stress, electron microscopy and differential proteomic analysis were performed on the critical feeding organ gill of the mussels after 9days of starvation. The electron microscopy results showed that the cilia of the mussel gills were dissolved, and the gaps between gill filaments widened under starvation. Differential proteomic analysis revealed that phagocytosis-related proteins such as ATPeV1E, ATPeV1C, LAMP1_2 and CTSL were significantly upregulated, and the phagocytosis pathway was significantly enriched (p < 0.05). In addition, the corin content in gill and myeloperoxidase level as well as the number of dead cells in blood were both significantly increased (p < 0.05). What's more, proteomic data suggested that immune maintenance, cellular transport and metabolism related pathways were significantly enriched, which illustrated an immune and metabolism responses under starvation. This study reveals for the first time that phagocytosis functions as an essential strategy for M. coruscus to cope with starvation, which provides new scientific knowledge and a theoretical basis for understanding the adaptation mechanisms of mussel to starvation and for rational optimization of mussel culture patterns.

A Global Survey of Hypervirulent Aeromonas hydrophila (vAh) Identified vAh Strains in the Lower Mekong River Basin and Diverse Opportunistic Pathogens from Farmed Fish and Other Environmental Sources.

Hypervirulent Aeromonas hydrophila (vAh) has emerged as the etiologic agent of epidemic outbreaks of motile Aeromonas septicemia (MAS) in high-density aquaculture of farmed carp in China and catfish in the United States, which has caused millions of tons of lost fish. We conducted a global survey to better understand the evolution, geographical distribution, and phylogeny of vAh. Aeromonas isolates were isolated from fish that showed clinical symptoms of MAS, and pure cultures were screened for the ability to utilize myo-inositol as the sole carbon source. A total of 113 myo-inositol-utilizing bacterial strains were included in this study, including additional strains obtained from previously published culture collections. Based on a gyrB phylogeny, this collection included 66 A. hydrophila isolates, 48 of which were vAh. This collection also included five new vAh isolates from diseased Pangas catfish (Pangasius pangasius) and striped catfish (Pangasianodon hypophthalmus) obtained in Cambodia and Vietnam, respectively. Genome sequences were generated from representative vAh and non-vAh isolates to evaluate the potential for lateral genetic transfer of the myo-inositol catabolism pathway. Phylogenetic analyses of each of the nine genes required for myo-inositol utilization revealed the close affiliation of vAh strains regardless of geographic origin and suggested lateral genetic transfer of this catabolic pathway from an Enterobacter species. Prediction of virulence factors was conducted to determine differences between vAh and non-vAh strains in terms of virulence and secretion systems. Core genome phylogenetic analyses on vAh isolates and Aeromonas spp. disease isolates (55 in total) were conducted to evaluate the evolutionary relationships among vAh and other Aeromonas sp. isolates, which supported the clonal nature of vAh isolates. IMPORTANCE This global survey of vAh brought together scientists that study fish disease to evaluate the evolution, geographical distribution, phylogeny, and hosts of vAh and other Aeromonas sp. isolates. In addition to vAh isolates from China and the United States, four new vAh isolates were isolated from the lower Mekong River basin in Cambodia and Vietnam, indicating the significant threat of vAh to modern aquaculture and the need for improved biosecurity to prevent vAh spread.

Physiological responses to acute hypoxia in the liver of largemouth bass by alteration of mitochondrial function and Ca2+ exchange

Oxygen is a critical factor for most organisms and this is especially true for aquatic animals. Unfortunately, high-density aquaculture farming practices and environmental degradation will inevitably lead to hypoxic stress in fishes such as largemouth bass (Micropterus salmoides). Thus, characterizing the physiological responses during acute hypoxia exposure is extremely important for understanding the adaptation mechanisms of largemouth bass to hypoxia. The present study aimed to investigate mitochondrial function and Ca2+ exchange in largemouth bass under hypoxic conditions. Largemouth bass were subjected to hypoxia (1.2 ± 0.2 mg/L) for 24 h Liver mitochondria and endoplasmic reticulum (ER) parameters were analyzed. We used Liquid chromatography-mass spectrometry (LC-MS) to further elucidate the pattern of energy metabolism. Changes of Ca2+ concentrations were observed in primary hepatocytes of largemouth bass under hypoxic conditions. Our results indicate that the morphology and function of the mitochondria and ER were altered under hypoxia. First, the occurrence of autophagy was accompanied by reactive oxygen species (ROS) generation and electron transport chain (ETC) activity modulation under hypoxia. Second, hypoxia enhanced mitochondrial fusion and fission, mitochondrial biosynthesis, and ER quality control in the early stages of hypoxic stress (before 8 h). Third, hypoxia modulated tricarboxylic acid (TCA) cycle flux and caused the accumulation of TCA intermediate metabolites (citric acid and oxoglutaric acid). Additionally, Ca2+ efflux in the ER was observed., and the genes for Ca2+ transporters presented high expression levels in cellular and mitochondrial membranes. Collectively, the above physiological responses of the mitochondria and ER contributed to maintaining energy production to withstand the hypoxic stress in largemouth bass. These results provide novel insights into the physiological and metabolic changes in largemouth bass under hypoxic conditions.

Sustained oxygen release of hydrogen peroxide-acrylic resin inclusion complex for aquaculture

Abstract To overcome the lack of dissolved oxygen in high-density aquaculture water, a hydrogen peroxide-acrylic resin inclusion complex with sustained oxygen releasing effect was designed and prepared. The resin was synthesized by emulsion polymerization of acrylic acid, methyl methacrylate and butyl acrylate in a mass ratio of 2: 3: 5, and neutralized with sodium hydroxide solution by 50%. The resin solution was mixed in a mixture of urea and 30% hydrogen peroxide solution (CO(NH2)2: H2O2, 1: 1, mol: mol), and dried at 40 °C for 4 h to obtain the hydrogen peroxide-acrylic resin inclusion complex. The product with 4.0% resin by mass of hydrogen oxygen solution, could release oxygen for 92 h in pond water. After optimization by adding a small amount of NaCl, Na2SO4, and EDTA, it was mixed with calcium carbonate and magnesium stearate in a mass ratio of 5: 4: 0.9, and pressed into tablets (1.2 × 0.6 cm, 0.99 g). One tablet in 50 L simulated micro ecosystem aquaculture water with 20 of Carassius auratus fish could release oxygen for 116 h and brought fish with 83.3% of survival rate higher than 51.7 and 70.0% of blank and sodium percarbonate groups.

Study of the Effect of Dietary Agavin Supplementation in Blood Parameters and Antioxidant Enzymes of Juvenile Nile Tilapia (Oreochromis niloticus) under Stress Conditions

High-density aquaculture produces oxidative stress that affects fish welfare and leads to poor growth. Agavin is a fructan that regulates the antioxidant response and inhibits stress-related alterations in blood metabolites (cortisol and blood lipids), preventing oxidative damage in fish. This study evaluated the effect of dietary agavin on the hepatic antioxidant response and blood metabolites in Nile tilapia under high rearing density. A negative control, a positive control, and experimental diets supplemented with 20 and 40 g/kg agavin were formulated. Nile tilapia (1.04 g ± 0.01 g initial body weight) were fed for 80 days to evaluate the antioxidant response and blood metabolites. After 90 days, fish were exposed to high density (63 kg/m3) for twenty days, except for the negative control (low-density). Under high-density stress, cortisol, cholesterol, and triglyceride levels decreased in fish fed diets with agavin compared with the positive control (high density). CAT and SOD activity significantly increased in fish fed agavin diets; malondialdehyde levels decreased under high density compared with both controls. These results suggest that dietary agavin supplementation promotes the antioxidant response and prevents stress-related alterations in blood parameters in Nile tilapia under high rearing density through its antioxidant properties and, probably, has a prebiotic effect.

The Impact of Floating Raft Aquaculture on the Hydrodynamic Environment of an Open Sea Area in Liaoning Province, China

The sea area of Changhai County in Dalian City is a typical floating raft aquaculture area, located in Liaoning Province, China, where a key issue in determining the scale and spatial layout of the floating raft aquaculture is the assessment of the impact of aquaculture activities on the hydrodynamic environment. To address this issue, we established depth-averaged two-dimensional shallow water equations and three-dimensional incompressible Reynolds-averaged Navier–Stokes equations for the open sea area described in this paper. The impact of floating rafts for aquaculture on hydrodynamic force was reflected in the numerical model by changing the Manning number, where scenarios with different aquaculture densities were taken into account. Finally, the water exchange rate of the floating raft aquaculture area in the study area was calculated. It was found, through a comparison between the simulated value and the measured value obtained via layered observation, that the two values were in good agreement with each other, indicating that the model exhibits great accuracy. In addition, the calculation results for scenarios before and after aquaculture were compared and analyzed, showing that from low-density to high-density aquaculture zones, the variation in flow rate was greater than 80% at the peak of a flood tide. The water exchange rates of the water body after 1 day, 4 days, and 8 days of water exchange were also calculated, and the results show that they had been reduced by 17.92%, 13.59%, and 1.63%, respectively, indicating that the existence of floating rafts for aquaculture indeed reduced the water exchange capacity of the water body. The model described in this paper can serve as a foundation for other studies on aquaculture in open sea areas, and it provides a theoretical basis for the scientific formulation of marine aquaculture plans and the rational optimization of the spatial layout.

Hypoxia alters glucose and lipid metabolisms in golden pompano (Trachinotus blochii)

Sufficient dissolved oxygen (DO) is essential for most teleosts. However, high-density aquaculture and fluctuating environmental factors can result in hypoxic stress in golden pompano (Trachinotus blochii). In this study, physiological, biochemical and transcript indicators of metabolism and apoptosis were investigated in T. blochii under hypoxic conditions (1.9 ± 0.2 mg/L) for 12 h. Increases in the content of lactic acid (LD) and the activity of lactate dehydrogenase (LDH), pyruvic acid (PA), phosphofructokinase (PFKA), and hexokinase (HK) suggested the enhancement of anaerobic glycolysis under hypoxic stress. Furthermore, significant increases in triglycerides (TGs) and lipoprotein lipase (LPL) in the liver under hypoxic stress for 6 h and a high level of carnitine palmitoyltransferase-1 (CPT-1) under hypoxic stress for 12 h indicated activation of lipid utilization. Additionally, glycolysis/gluconeogenesis, sphingolipid metabolism, pentose phosphate, HIF-1, and p53 signaling pathways were activated in response to hypoxia. Eleven DEGs involved in these pathways were identified. The relative expressions of HIF-1α (Hypoxia Inducible Factor 1 Subunit Alpha), PGM (phosphoglucomutase), PFKA (6-phosphofructokinase 1), HK (hexokinase), SMPD3 (sphingomyelin phosphodiesterase 3), SPT (serine palmitoyltransferase), and EPO (erythropoietin) were up-regulated under hypoxic conditions. Additionally, the relative expressions of RGN (gluconolactonase), CCNG2 (cyclin G2), CERS1 (sphingoid base N-stearoyltransferase 1), and IGFBP3 (insulin-like growth factor-binding protein 3) were down-regulated. This research reveals metabolic changes and cell apoptosis activation in T. blochii under hypoxic conditions, providing new insight into metabolic responses to hypoxia in teleosts.