Fish Gills Research Articles

Transcriptome analysis reveals hypoxic response key genes and modules as well as adaptive mechanism of crucian carp (Carassius auratus) gill under hypoxic stress

Fish gill tissue is a primary organ responsive to acute oxygen deprivation or dissolved oxygen (DO) fluctuations in aquatic environments. However, the adaptive mechanism of crucian carp to hypoxic stress remains largely unknown. Here, we investigated gill physiological and transcriptomic changes of crucian carp exposed to hypoxic conditions (dissolved oxygen concentration of 0.6 ± 0.3 mg/L) for different durations (0 d, 1 d, 2d, 3d, 4 d, and 5d). Transcriptomic analysis revealed that the hypoxia group (0.6 ± 0.3 mg/L DO) exhibited a reduction in interlamellar cell mass (ILCM) on the gill filaments, compared with the control group (6.6 ± 0.3 mg/L DO). With prolonged hypoxia stress, the epithelial cells in the gill lamellae became sparse at 3 d to 5 d, and gill vacuoles were increased. A total of 3,502 differentially expressed genes (DEGs) were identified, and 3 hypoxia-specific modules were screened through differential expression analysis, weighted gene co-expression network analysis (WGCNA), and Bayesian network analysis. The apoptosis, necroptosis, efferocytosis and FoxO signaling pathways were significantly enriched based on the KEGG enrichment pathway analysis. The VEGF pathway genes are significantly expressed, enhancing the generation of microvessels in the gill filaments, and improving the capacity to carry oxygen, thus enabling the crucian carp to adapt to hypoxia stress. Hypoxia activated glycolysis, enhanced anaerobic metabolism, promoted β-oxidation of fatty acids, providing energy and maintaining normal physiological metabolism, eventually improving antioxidant and immune capabilities in crucian carp. In summary, this study reveals the molecular mechanism by which crucian carp adapt to hypoxic stress. Our findings provide valuable references for promoting the healthy aquaculture of hypoxic-sensitive fish and breeding hypoxia-tolerant fish varieties.

Comparative Study of Electrophoretic Patterns of Protein Sub Units in Various Tissues of Two Fresh Water Fishes (Heteropneustes fossilis and Labeo rohita) Through Gel Electrophoresis

The present investigation is determine the comparative study of electrophoretic patterns of protein sub units in two different fishes i.e. Heteropneustes fossilis and Labeo rohita. All the tissues were examined on 7.5% SDS-PAGE. In this investigation we observed gill, liver, intestine, muscle and brain tissues of both fishes. In this Gill and Muscle tissues of two fishes exhibits highest protein bands (10 and 7 respectively). The lowest bands are observed in intestine in both fishes(7,5 respectively).In this investigation we observed homology in protein bands with minor variations.

The Atlantic salmon gill transcriptional response to natural infection with HPR0-ISAV (Isavirus salaris) in three Norwegian smolt farms.

Infectious Salmon Anaemia virus (ISAV) is an orthomyxovirus that causes large economic losses in Atlantic salmon (Salmo salar L.) aquaculture. All virulent ISAV variants originally emerged from a non-virulent subtype, ISAV-HPR0. Transient ISAV-HPR0 infections are common in both freshwater and marine environments. ISAV-HPR0 infects juveniles, marine salmon at on-growing sites, and broodstock salmon. The shift in virulence from ISAV-HPR0 to the virulent HPRΔ is suggested to be a stochastic event that depends on the virus's replication frequency. Therefore, reducing the capacity to maintain ISAV-HPR0 infection within individual farms may limit the risk of emerging pathogenic ISAV variants and ISA disease. The absence of infection-related clinical signs and the lack of experimental models limit our understanding of ISAV-HPR0-host interactions. We characterise the host transcriptional response to natural ISAV-HPR0 infection, using Atlantic salmon gill tissues collected on three Norwegian smolt farms. The comparison of all infected (qPCR-positive) and non-infected (qPCR-negative) individuals revealed a classic antiviral response in the gills of ISAV-HPR0 infected fish in a site-independent transcriptomic analysis. Complementary analyses showed that the response to infection varied considerably between sites. Site-specific differences could be associated with a range of factors that are challenging to control in field studies, such as fish size, the stage of infection, and the presence of additional microorganisms. Our findings enhance our understanding of how Atlantic salmon respond to ISAV-HPR0 infection, pinpointing common HPR0-induced antiviral response genes. Future studies should investigate whether these candidate genes limit virus replication in the gill for risk of novel transitions to virulence.

Effects of the 2022 Oder River environmental disaster on fish gill structure.

The 2022 Oder River disaster was one of the most significant harmful events in recent European river history, with an estimated 60% reduction in fish biomass in the lower section of the river. While the prevailing hypothesis attributes associated fish kills to toxins from golden algae Prymnesium parvum, our histopathological study on the gills of 2 common cyprinid fish species, namely vimba bream Vimba vimba (L.) and roach Rutilus rutilus (L.), collected from the lower Oder River at 3, 4, and 6 mo after the disaster, suggests another mechanism. Vimba bream showed damage to the epithelial layer of lamellae and increased mucus production. Roach exhibited interlamellar cell mass (ILCM), lamellar damage, including hypertrophy of epithelial cells, lamellar fusion, as well as significant thickening of the water-blood barrier compared to controls. These findings suggest that adverse factors, most likely the increase in toxin concentrations resulting from reduced water levels together with elevated temperatures and low precipitation, triggered the formation of ILCM, increasing the susceptibility of fish to hypoxia. Fish species with a capacity for adaptive interlamellar hyperplasia, such as common bream Abramis brama, roach, and common perch Perca fluviatilis, accounted for the largest number of deaths during the disaster. Vimba bream, which showed no ILCM, were observed only sporadically, with mortality confined to a single area of the Oder. In conclusion, fish capable of adaptive hyperplasia, whereby the gills attempt to protect themselves by developing ILCM, appear to be particularly vulnerable in conditions of aquatic hypoxia.

Deciphering spread of quinolone resistance in mariculture ponds: Cross-species and cross-environment transmission of resistome.

Mariculture is known to harbor antibiotic resistance genes (ARGs), which can be released into marine ecosystems via oceanic farming ponds, posing a public health concern. In this study, metagenomic sequencing was used to decipher the profiles of quinolone-resistant microbiomes and the mechanisms of quinolone resistance in sediment, seawater, and fish gill samples from five mariculture ponds. Residues of both veterinary-specific (enrofloxacin and sarafloxacin) and prohibited quinolones (ofloxacin, ciprofloxacin, pefloxacin, norfloxacin, and lomefloxacin) were detected. We identified a total of 285 subtypes of ARGs across all samples. Pathogens played a crucial role in the prevalence and distribution of these ARGs. Out of the annotated 629 bacterial species, 42 were identified as pathogenic, predominantly belonging to the Proteobacteria phylum. Notably, the Acinetobacter genus was prevalent in the gills and exhibited correlations with various ARGs. The presence of the plasmid-mediated quinolone resistance (PMQR) genes in various bacterial species and the identification of sulfonamide resistance genes across different samples indicated the potential for cross-species and cross-environment transmission of ARGs. Metagenomic binning revealed that Exiguobacterium harbored five ARGs (vanA, vanB, fexA, msr(G), mefF), while Shewanella carried six ARGs (blaOXA-436, adeF, qacl, ANT (2'')-Ia, dfrA1, rsmA). Mutations in gyrA and parC contributed to quinolone resistance in these multidrug-resistant Exiguobacterium and Shewanella. Our findings suggest a potential for ARG transmission across various bacterial species and environments in mariculture. This study emphasized the risk of resistance spread within the mariculture ecosystem.

Repurposing of a gill gene regulatory program for outer ear evolution.

How novel structures emerge during evolution has long fascinated biologists. A dramatic example is how the diminutive bones of the mammalian middle ear arose from ancestral fish jawbones1. In contrast, the evolutionary origin of the outer ear, another mammalian innovation, remains a mystery, in part because it is supported by non-mineralized elastic cartilage rarely recovered in fossils. Whether the outer ear arose de novo or through reuse of ancestral developmental programs is unknown. Here we show that the outer ear shares gene regulatory programs with the gills of fishes and amphibians for both its initial outgrowth and later development of elastic cartilage. Comparative single-nuclei multiomics of the human outer ear and zebrafish gills reveals conserved gene expression and putative enhancers enriched for common transcription factor binding motifs. This is reflected by transgenic activity of human outer ear enhancers in gills, and fish gill enhancers in the outer ear. Further, single-cell multiomics of the cartilaginous book gills of horseshoe crabs reveal a shared DLX-mediated gill program with vertebrates, with a book gill distalless enhancer driving expression in zebrafish gills. We propose that elements of an invertebrate gill program were reutilized in vertebrates to generate first gills and then the outer ear.

Sublethal Urea Exposure in Nile Tilapia: Morphological, Behavioural, and Histological Alteration.

The pace of research efforts has been extraordinarily accelerated across the globe to address the contamination issues caused by pesticides, and fertilizers, especially in the aquatic ecosystem. The sole aim of this study was to assess the effect of urea on Nile Tilapia (Oreochromis niloticus). For this purpose, the fish fingerlings were exposed to increasing concentrations of urea such as 0, 1, 2.5, 5, 10, 20, and 40 g/l for 72 hr. Survival analysis suggested a strong correlation between the increasing doses of urea and the mortality rate among tested fingerlings. This study reported remarkable morphological, and behavioural alternation such as increased operculum movement, bottom-dwelling, lethargy, secretion of mucus, reduction in food intake, and bleeding in the fin and around the mouth in the treated group. Haematological analysis revealed that a significant reduction in RBC count and Hb along with an increase in WBC number is associated with urea toxicity. Our study showed a significant rise in glucose concentration upon urea toxicity in Nile tilapia fingerlings for the first time, emphasizing the adverse effect of fertilizers on carbohydrate metabolism. Significant rises in the enzymatic activity such as alanine aminotransferase (ALT), alkaline phosphatase (ALP), and aspartate aminotransferase (AST) upon urea treatment emphasize the possibilities of liver damage, biliary obstruction, and abnormal glucose metabolism. Histological analysis of urea-treated fish compared to normal fish revealed that urea toxicity drastically altered the tissue architecture of fish's gills, eyes, intestine, and stomach. As the visual systems of mammals and fish resemble in more aspects, our findings may be useful in understanding the impact of pollutants on sensory organs concerning humans. We conclude that our findings highlight the importance of urea toxicity on Nile tilapia fingerlings and invite multidisciplinary research to uncover molecular mechanisms underlying urea toxicity.

Analysis of Microplastic Contamination and Associated Human Health Risks in Clarias gariepinus and Oreochromis niloticus from Kubanni Reservoir, Zaria Nigeria

Environmental safety has become a major concern in recent years due to the global increase in microplastic pollution. These ubiquitous, tiny, and potentially toxic plastic particles enter aquatic environments through weathering of larger plastics and the release of microbeads. Although numerous studies have focused on microplastic pollution in developed regions, information from developing countries remains limited. This study assessed the presence of MPs and associated oxidative stress responses in two commercial fish species, Clarias gariepinus (Catfish) and Oreochromis niloticus (Nile Tilapia), from Kubanni reservoir, Zaria, Nigeria, over six months spanning both the dry and rainy seasons. Fibers were identified as the most abundant MP particles, followed by fragments, films, and beads, in the order of fibers > fragments > films > beads. The highest fiber concentrations were recorded in the gills, with Clarias garipinus showing 11.5 MP items/individual and Oreochromis niloticus showing 22.5 MP items/individual. Black microplastics were predominant, and the most common ingested MP ranged from 1.0 to 2.0 mm. The primary polymers identified were polypropylene and polyethylene terephthalate. Evidence of oxidative stress and cellular damage was observed in the gills, liver, and dorsal muscles of both fish species, which correlated with MPs ingestion. According to recommendations from the European Food Safety Authority regarding fish consumption by children and adults, individuals consuming Clarias gariepinus and Oreochromis niloticus from the Kubanni reservoir may be exposed to between 70 and 700 MP items/organ. The risk associated with consuming MPs found in fish gills and guts was notably higher, posing significant concerns for human health. This study provides insights into microplastic contamination in commercially important fish from the Kubanni Reservoir and highlights the environmental and public health risks associated with consuming contaminated fish from this ecosystem.

Assessment of Total Protein Contents, Hematological Parameters and Histopathological Alterations in Gills of Fish Treated with Plasticizers, Di-Methyl Phthalate and Di-N-Octyl Phthalate

Assessment of Total Protein Contents, Hematological Parameters and Histopathological Alterations in Gills of Fish Treated with Plasticizers, Di-Methyl Phthalate and Di-N-Octyl Phthalate

Comparative evaluation of the adverse effects wastewater effluents on Channa punctata through oxidative stress and histopathological alterations

This study investigates the adverse effects of wastewater effluents on Channa punctata, collected from upstream (Methwasa), point-source (Juna Nagda), and downstream (Parmarkheri) locations along the Chambal River at Nagda, Ujjain, India. The research focuses on oxidative stress responses and histopathological alterations in fish gills, liver, and kidneys. Catalase and glutathione S-transferase activities were significantly higher at Juna Nagda and Parmarkheri compared to the upstream site (Methwasa) (p < 0.05), suggesting the activation of antioxidant defense mechanisms due to pollution exposure. Histological analysis revealed the most severe tissue damage in fish from Juna Nagda, followed by Parmarkheri and Methwasa. The Integrated Biomarker Response (IBR) for oxidative stress and histopathological changes consistently indicated higher values at the polluted sites. Water temperature, electrical conductivity (EC), and nitrate levels were identified as potential factors influencing these biomarker responses. The study concludes that thermal effluents discharged into Juna Nagda are responsible for the observed effects. Overall, integrated biomarkers, particularly histopathological alterations, offer a reliable tool for monitoring the prolonged impacts of wastewater effluents on aquatic organisms.

The adverse effects of nanosilver on fish gills: A critical review on ecotoxicity and underlying mechanism.

The environmental safety and health impacts of nanosilver have attracted much attention due to their continuous detection in water. Although the effects of nanosilver on aquatic organisms have been reported, the ecotoxicity and underlying mechanism of nanosilver in aquatic organisms are not fully understood. Fish gills are the primary target organs of pollutant exposure in aquatic environments, and is important to clarify the impact of nanosilver on aquatic organisms by systematically and comprehensively revealing the effect of nanosilver on fish gills. Here, we review the ecotoxicity and potential mechanisms of nanosilver on fish gills. Studies have shown the most commonly used and toxic nanosilver for studying the effects of nanosilver on fish gills is 5-30 nm. Nanosilver mainly affects various physiological functions of fish gills, such as respiration, ion, and osmotic pressure regulation, by disrupting the structure and components of tissues or cells (e.g., cell membranes and mitochondria), as well as interfering with tissue lipid, amino acid, and carbohydrate metabolism. The main mechanisms of toxicity induced by nanosilver in fish gills are gill membrane damage, oxidative stress, and silver ion release. This review provides a scientific basis for the detrimental effects of nanosilver on aquatic ecological environment health and the protection of fish resources.

Gill Health in Fish Farmed in Recirculating Aquaculture Systems (RAS): A Review.

Recirculating Aquaculture Systems (RAS) have been proposed as the future of aquaculture, because they can be used anywhere regardless of access to water, they offer high level of control over farming environment, including biosecurity, and are considered to be sustainable. However, despite of continuous development, there can be still issues with water quality affecting gill health of fish farmed in these systems. This review provides an overview of fish gill structure and gill immune response, and discusses the known impacts of RAS on gill health. Several experimental studies have inadequately reported conditions, particularly water quality, making it difficult to determine if the observed effects were due to water quality issues or RAS system itself. It is crucial for studies investigating the impact of RAS on fish to report water quality during the study. Furthermore, assessments of RAS effects on gill health should include sufficient independent replicates and flow through controls using a common water source. Various methods have been used to assess gill health in RAS, including gill histology, presence of pathogens, gene expression in the gills and gill microbiome analysis. Differences in gill health in fish from RAS and a flow through system have been shown for a number of freshwater and marine fish species. However, these results have been inconsistent across studies, and some results have been challenging to interpret as indicators of gill health. Holistic studies including a number of different methods to assess fish gills would give more conclusive results. More research is needed, in particular, on brackish and marine RAS, to fully understand their impacts on gill health.

Effects of Micro Plastics on Fishes of Hooghly River, India

Plastic pollution is now a concerning issue which destroying the riverine ecology silently. Excessive use of plastics & indifference to removing plastic waste after use gives birth to microplastics. Rivers are the major track way which can caught plastic debris from surrounding landside & contaminate the aquatic life without degraded the matter for a long time. The research was conducted on the Hooghly river near Barrackpore in the West Bengal region of India. The research explores the matter of microplastics contamination in various fish species of Hooghly river & effects of microplastics in the fish body according to the size, concentration, physical component & polymerase type of microplastic. Mainly 0.3 mm to 5 mm sizes microplastics have been noticed in both fish & shore sediments of this river site. Mostly the fiber & fragment type microplastics elements were damage the liver & gill of fish badly.

Mechanism of acclimation to chronic intermittent hypoxia in the gills of largemouth bass (Micropterus salmoides).

The acclimation response of fish gills to chronic intermittent hypoxia (CIH) is an important aspect to understand, as anthropogenically induced hypoxia in water bodies has been a stressor for fish for many years and is expected to persist in the future. In order to investigate the acclimation response of fish gills to CIH stress, we conducted a study using largemouth bass (Micropterus salmoides) exposed to intermittent hypoxia (dissolved oxygen level, 2.0mg·L-1) for either 1 or 3h per day, over a period of 8weeks. Our findings indicate that exposure to CIH induced remodeling of the gills and an increase in gill surface area. This remodeling of the gills may be attributed to changes in cell growth and proliferation, which are influenced by the activation of the MAPK signaling pathway. We also observed significant upregulation of genes related to glycolysis (fba, pgam1, pepck, atp-pfk, pfk-2, g6pi, gapd-1, and pk), while genes associated with cholesterol synthesis (3β-hsd, cyp51, dsdr- × 1, dsdr, and dhcr7) were downregulated following CIH exposure. Furthermore, we observed the presence of elongated megamitochondria in mitochondria-rich cells within the gills of fish exposed to hypoxia. Additionally, numerous genes involved in calcium signaling pathways were upregulated in the gills of largemouth bass, suggesting an enhanced sensitivity of gills to environmental cues in hypoxia conditions. However, the expression levels of certain genes related to innate and adaptive immune responses were inhibited following CIH exposure. Moreover, the number of mucous cells decreased after CIH exposure. This may have made the gills more susceptible to infection by pathogens, although it facilitated oxygen uptake. These findings highlight the potential vulnerability of gills to pathogenic organisms in the presence of CIH. Overall, our study contributes to a better understanding of how fish acclimate to CIH.

Histopathology of the Haplorchis taichui infection in the freshwater fish, Tigris kingfish, and Tigris barb (Cypriniformes: Cyprinidae) from Iran.

Flukes can cause severe and lethal diseases in various animals, including fish. Both adult and larval stages of flukes are found in fish. Haplorchiasis is an infection of fish gills by heterophyid trematodes such as Haplorchis taichui. To detect this parasite, the gills of 30 Tigris kingfish and Tigris barb collected from the Shapour River in Kazerun, Fars province were found to be parasitized with metacercarial cysts of a heterophyid trematode identified as H. taichui. Histopathological examination of the infected fish gills revealed cartilage proliferation, severe hyperplasia, fusion, S-forming, shortening and thickening, distortion, and displacement of affected secondary gill filaments leading to deformities of the filament structure, clubbing, telangiectasis, and hyperemia. Although the gill damage was evident and potentially life-threatening for the cyprinid fish, the examined fish showed no clinical signs. This finding indicates that H. taichui is pathogenic; therefore, prevention of infection and treatment should be a priority.

Activity pattern of antioxidant enzymes in relation to the time of exposure of hexavalent chromium to Nile tilapia Oreochromis niloticus.

Hexavalent chromium (Cr (VI)), a toxicant of environmental concern, frequently enters into water bodies and produces oxidative stress in fish. The antioxidant enzymes, Superoxide dismutase (SOD), Catalase (CAT), and Glutathion S-transferase (GST) are activated to counteract the oxidative stress in fish. This study explores the pattern of activation of these enzymes in gill, muscle, liver, and kidney tissues of Nile tilapia Oreochromis niloticus exposed to 9.35 mg/L and 18.70 mg/L of Cr (VI) for 96 h. The optimal hour of activity of these enzymes was revealed through extensive regression analysis. The results indicate a bell-shaped time response curve in the activity of the enzymes in both the treatments, except CAT in the gill of fish exposed to 18.70 mg/L Cr (VI) and GST in the gill, liver, and kidney of fish exposed to 18.70 mg/L Cr (VI). The results indicate that the optimal hour of activity of SOD changes in tandem with CAT, SOD responding first followed by CAT, both diminishing within 96 h. However, deviating from the bell-shaped pattern, the activity of CAT in gill and GST in gill, liver, and kidney in fish exposed to 18.70 mg/L Cr (VI) continued to rise even at 96 h, indicating that these antioxidant enzymes could not diminish the oxidative stress produced by the higher dose of Cr (VI). It was concluded that the activity of SOD, CAT, and GST between 30 and 70 h in the gill, liver, and kidney of Nile tilapia could serve as excellent biomarkers of oxidative stress under low doses of Cr (VI).

Acclimation temperature and parasite infection drive metabolic changes in a freshwater fish at different biological scales

Abstract Environmental stressors such as elevated temperature and parasite infection can impact individual energy metabolism. However, organismal responses to co‐occurring stressors and their effects across biological scales remain unexplored despite the importance of integrative studies for accurately predicting the resilience of natural populations in changing environments. Using wild‐caught, naturally parasitized pumpkinseed sunfish, Lepomis gibbosus, we quantified changes in cellular and whole‐organism metabolism in response to temperature and parasite infection. We acclimated pumpkinseeds for 3 weeks at 20°C, 25°C or 30°C before measuring whole‐organism oxygen uptake (ṀO2) using intermittent flow‐respirometry to quantify maximal and standard metabolic rates (MMR and SMR, respectively) and aerobic scope (AS). We also measured the maximal activity of enzymes [citrate synthase (CS), respiratory complexes I + III and IV of the electron transport system and lactate dehydrogenase (LDH)] linked with cellular bioenergetics in fish heart, brain, spleen and gills using spectrophotometry. We found no interactions between acclimation temperatures and parasite intensity on cellular or whole‐organism metabolism. However, both stressors were independently related to fish metabolism, with differing impacts across biological scales. Whereas MMR increased with acclimation temperature, this was not mirrored by increasing SMR or decreasing AS, suggesting thermal compensation across acclimation temperatures at the whole‐organism level. On a cellular level, acclimation responses were similar across organs, with maximal activity of all enzymes decreasing with increasing acclimation temperature. However, LDH activity remained higher than aerobic enzyme activities (CS, ETS complexes I + III and IV) across acclimation temperatures and organs, especially in gills, where LDH activity drastically increased at 30°C. This may indicate a stronger reliance on anaerobic metabolism to sustain whole‐organism metabolic performance at high temperatures. Fish with greater trematode infection had lower MMR. There were no relationships between parasite intensity and SMR, AS or maximal enzyme activity. Our work shows that co‐occurring stressors have distinct impacts on fish metabolism: parasites are primarily related to whole‐organism metabolism while temperature impacts metabolism across biological scales. This highlights that interactions among co‐occurring stressors are important for ecological realism and accurate predictions regarding population resilience to environmental changes. Read the free Plain Language Summary for this article on the Journal blog.

Enhanced efficacy of Magnolia denudata essential oil in fish anesthesia using nanoemulsions and self-microemulsifying drug delivery systems.

The use of plant essential oils as anesthetics for fish has gained increasing attention, but ethanol, often used as a co-solvent, presents certain limitations. Recently, Magnolia denudata essential oil (MDO) has emerged as a promising alternative for fish anesthesia and sedation. To further improve MDO anesthesia efficacy, this study developed nanoemulsion (NE) and self-microemulsifying drug delivery system (SMEDDS) formulations of MDO. Transmission electron microscopy and stability tests confirmed that both NE and SMEDDS possess smaller particle sizes and are stable under various temperature conditions. Anesthetic trials on fish demonstrated that these formulations reduced the time needed to induce anesthesia compared with the non-formulations. Additionally, physiological assessments of the fish gills showed that neither NE nor SMEDDS caused irreversible damage to respiratory function. Overall, NE and SMEDDS present a safe and effective delivery system for MDO, enhancing its anesthetic properties while minimizing potential harm to aquatic organisms compared to traditional methods.

Increased metabolic demand reveals morpho-functional impacts caused by settleable atmospheric particulate matter on fish gills

Exposure to environmentally relevant levels of settleable atmospheric particulate matter (SePM) limits the aerobic performance of inactive healthy adult fish. We evaluated the gill morpho-functional impacts (gill structure and ionic balance) caused by SePM exposure (96 h) in Nile tilapia when fish is impelled to maximal aerobic swimming effort. In control fish, swimming reduced epithelial filament thickness (EFT, 25 %), increased the distance between lamellae (DL, 21 %), and reduced the plasma Na+ (5 %). In resting fish, SePM exposure increased EFT (11 %), reduced DL (30 %), lamellar height (LH, 18 %), and plasma Na+ (4 %), whereas increased Cl- and K+ (8 % and 20 %). In SePM-exposure fish, swimming reduced EFT (40 %), increased DL (30 %) and LH (30 %), while reduced Na+ and Cl- (9 % and 18 %), and increased K+ when compared to inactive SePM-exposed fish. These morpho-functional limitations may compromise whole-body maintenance and swimming recovery, affecting the fish ability to perform at higher activity levels.

Gill and brain transcriptomic analysis of mandarin fish(Siniperca chuatsi)reveals hypoxia-induced mitochondrial dysfunction and modulation of metabolism

The oxygen content in the fish ponds is facing greater challenges than before in the aquaculture of mandarin fish (Siniperca chuatsi) due to the change of climate and eutrophication. Until now, little is known about the molecular mechanisms underlying the harmful effects of hypoxia on this species. In this work, we built transcriptomes for the mandarin fish that were exposed to decreased oxygen concentration at two times points (24 h and 96 h). The respiratory metabolism activities of pyruvate kinase (PK), hexokinase (HK), lactate dehydrogenase (LDH), succinate dehydrogenase (SDH) and malate dehydrogenase (MDH) had different significantly changes during hypoxic treatment. Histological observation of the gill and brain also revealed some damages by hypoxia. A total of 196,355 transcripts were involved in the Gene Ontology analysis, and the numbers of differentially expressed genes (DEGs) in the brain and the gill between the control and experiment groups are 141 and 552 respectively involved in the different hypoxic stress time. The DEGs were then analyzed using KEGG enrichment analysis. The results showed significant differences in the expression of some genes involved in ribosome pathways,biosynthesis of amino acids, hippo signaling pathway, and pentose phosphate pathway,glycolysis/gluconeogenesis pathway and the TCA cycle. The huge number of transcriptome sequences collected in this study has enhanced the mandarin fish gene resources, and the identified DEGs and related pathway analysis give essential information for understanding biological responses to hypoxia.