Diseased Fish Research Articles

Assessment of Fungi Infection on Clarias anguillaris (Linnaeus, 1758) and Oreochromis niloticus (Linnaeus, 1758), Two Fish Species Farmed in Burkina Faso

Worlwide, fungi are by far the most common pathogen in fish farming. They are responsible of important economic losses in the fishery sector. However, in Burkina Faso knowledge of fungi infecting farmed fish are scarce. As a consequence, the prevalence as well as the effect of these pathogens are not known. A study was carried out on fungal infection of farmed fish. It aimed to evaluate the diversity of fungi associated with Oreochromis niloticus (Linnaeus, 1758) and Clarias anguillaris (Linnaeus, 1758) farmed in Burkina Faso. In total, 89 individuals of fish consisted of 47 specimens of Oreochromis niloticus and 42 specimens of Clarias anguillaris were collected from eleven fish farms. Swabs were taken on fish bodies and inoculated in Malt Extract Agar (MEA). The chloramphenicol was added to avoid bacterial contamination. Seventy-seven (77) fish were infected by fungi (85.51%). Four genera including Aspergillus (four species), Rhizopus (one species), Penicillium (one species) and Mucor (one species) were isolated. Small and big fish were all infected. This study shows fungi as a potential factor that impacts fish farming and suggests a need for more research on their effect on fish. Knowledge of fish parasites like fungi will allow to set effective means of fish pathology control, which once implemented will lead to an increase in fish farming productivity.

Temperature Adaptation in the Postembryonic Development of Acanthocephalus tenuirostris (Palaeacanthocephala: Echinorhynchidae)

Under experimental conditions, the larval development of a fish parasite, Acanthocephalus tenuirostris was studied. This species is common in the eastern regions of Russia from Primorye Territory to the upper reaches of the Kolyma River. The material for the experiments was collected in different areas of the Magadan region which is located mainly in the subarctic climate zone. In several series of experiments, the infection and maintenance of intermediate hosts, the isopod Asellus hilgendorfii, took place at a constant temperature 15°C. In all cases, no more than 45 days were required for the formation of the final cystacanth stage. At the same time, in the hemocoel of isopods a large number of other larval stages were present simultaneously with cystacants. An additional experiment was conducted for the first 45 days at 15°C and the next 207 days at 4–6°C, showed the possibility of further development of larvae at low temperatures. Based on the comparison with the data available in the literature on the development times of European Acanthocephalus species living in temperate climates, it is concluded that the A. tenuirostris has anadaptation to a cold climate, whichprovides a twofold acceleration of the rate ofits development relative to larval A. lucii in Europe.

Nourishing Aquatic Life: A Comprehensive Reviewing of Fish Feed Strategies and Disease Combat in Aquaculture

With an increasing focus on creating sustainable methods that satisfy the nutritional requirements of aquatic life while successfully containing disease outbreaks, aquaculture has emerged as a crucial element of global food security. Nourishing Aquatic Life: A Comprehensive Review of Fish Feed Strategies and Disease Combat in Aquaculture explores the delicate balance between disease management and feed optimization, two crucial factors influencing the ecological sustainability and productivity of aquaculture systems. Innovative substitutes, including plant-based proteins, insect meal, and microbial sources, are being assessed alongside conventional fish feed formulations, which rely on fishmeal and fish oil to lessen environmental stresses while preserving high nutritional value. This article also covers how probiotics, prebiotics, and immunostimulants can improve fish immunity and resilience against common diseases, lowering the need for antibiotics and the likelihood of resistance. Additionally, we look at the most recent developments in fish feed formulation using biofloc, genetic engineering, and nanotechnology, emphasizing their implications for better fish health and disease resistance. These innovative strategies offer a hopeful vision for the future of aquaculture, inspiring us to continue our efforts in this field.

Aquatic Fungi and Fungal Diseases of Fish: A Review

Aquatic Fungi and Fungal Diseases of Fish: A Review

Unveiling the potential of parasites as proxy bioindicators for water quality assessment in river Jhelum Kashmir, India.

This study aimed to evaluate the effects of deteriorated physicochemical conditions in the river Jhelum on parasitic infestations and to investigate the potential of fish parasites as bioindicators of water quality. All the physicochemical parameters exhibited statistically significant differences based on both site and season (p < 0.01).The interaction term (Site × Season) was also kept in the model since it was statistically significant (p < 0.01). A parasitological survey of 360 schizothoracine fish revealed a 30.3% prevalence (109/360) of endohelminth infection. The study identified four predominant parasitic taxa across two distinct classes: Cestoda, including Adenoscolex oreini and Schyzocotyle acheilognathi, and Acanthocephala, comprising Pomphorhynchus kashmirensis and Neoechinorhynchus manasbalensis. For the assessment of parasitic load, we calculated the prevalence, mean intensity, mean abundance, and index ofinfection for each sampling period. Correspondence analysis identified associations between parasite occurrence and specific water quality parameters. Regression analysis, including R2 and p values, demonstrated a positive correlation between the number of parasites and both the proportion of infected fish and the ratio of infected to examined fish. Given that parasitic load is significantly influenced by a range of water quality parameters, fish parasites can serve as a robust indicator of declining water quality. Fish parasites are highly sensitive to water quality changes such as pollutants, toxins, and fluctuations in pH, temperature, and oxygen levels. Deteriorating water quality can stress fish, compromising their immune systems and increasing their susceptibility to parasitic infections. Additionally, complex life cycles of parasites can be disrupted by poor water conditions, making them indicators of water quality issues.

Potential Role of the Eastern Mosquitofish (Gambusia holbrooki) in the Spread of the Harmful Fish Parasite, Asian Tapeworm Schyzocotyle (Bothriocephalus) acheilognathi

Biological control of undesirable organisms and pathogens often involves the introduction of alien species into new regions. However, alien species themselves pose a potential threat to local ecosystems and economies. The Eastern mosquitofish Gambusia holbrooki is recognised as a dangerous invasive species, but despite this, it is still used for biological control of mosquito larvae, a potential vector of malaria plasmodium transmission to humans, on the Black Sea coast of the Caucasus. We focused on the species composition of helminths in this fish species. We detected adult nematodes Pseudocapillaria (Pseudocapillaria) tomentosa and cestodes Schyzocotyle acheilognathi (formely Bothriocephalus acheilognathi). The above nematode was observed for the first time in fish of the genus Gambusia. Importantly, the cestode S. acheilognathi, which we found in G. holbrooki, is the most successful invasive alien parasite species in freshwaters of the planet and is extremely hazardous to natural ecosystems and aquaculture as it can cause mass mortality of young fish. Thus, the current practice of transferring mosquitofish between water bodies on the Black Sea coast of the Caucasus to control mosquito larvae may contribute to the undesirable spread of a harmful quarantine fish parasite.

Fish Snx27 promotes viral products by modulating the innate immune response and exosomal machinery.

Viral nervous necrosis caused by the nervous necrosis virus (NNV) poses a significant threat to the global aquaculture industry. Developing preventive methods to minimize economic losses due to NNV infections is crucial. This study explored the role of the sorting nexin 27 (Snx27) gene, encoded by the orange-spotted grouper (Epinephelus coioides) and referred to as EcSnx27, as an immune regulator affecting red-spotted grouper nervous necrosis virus (RGNNV) infection in vitro. Our findings revealed that EcSnx27 negatively regulates interferon (IFN)-related cytokines and the promoter activities of fish ISRE and NF-κB. Furthermore, we identified the SNX-FERM and SNX-FERM-like domains as responsible for the interaction between EcSnx27 and RGNNV coat protein. Through the detection of viable virions associated with EcSnx27-containing exosomes, we propose that EcSnx27 may contribute to the release process of RGNNV by influencing the apoptosis-linked gene 2-interacting protein X (ALIX)-associated exosomal pathway. Consequently, our study suggests that EcSnx27 promotes RGNNV replication by inhibiting the IFN immune response and facilitating virus production and release through ALIX-mediated exosomal machinery.IMPORTANCERed grouper nervous necrosis virus (RGNNV), a member of the Nodaviridae family, has emerged as a significant cause of fish diseases worldwide, leading to high morbidity and mortality rates. This study investigated the sorting nexin 27 (Snx27) gene encoded by the orange-spotted grouper (Epinephelus coioides) on RGNNV infection in grouper kidney cells. Our findings revealed that EcSnx27 negatively regulated the interferon pathway, resulting in the promotion of RGNNV replication. Additionally, we observed that EcSnx27 could interact with apoptosis-linked gene 2-interacting protein X (ALIX) and the RGNNV coat protein, suggesting its potential involvement in viral release processes through modulation of the exosomal pathway. Our study identified EcSnx27 as a key target that RGNNV exploits to enhance viral production. This finding offers valuable insights into the immune evasion and viral release mechanisms of non-enveloped RNA viruses.

Microbiome and network analysis reveal potential mechanisms underlying Carassius auratus diseases: The interactions between critical environmental and microbial factors

Despite the rapid development of research on aquatic environment microbiota, limited attention has been paid to exploring the complex interactions between microbial communities and aquatic environments. Particularly, the mechanisms underlying fish diseases based on such dynamic interactions remain unknown. This study aimed to address the gap by conducting microbiome and co-occurrence network analyses on the typical freshwater aquaculture systems. High-throughput 16S rRNA gene sequencing results revealed significant differences in the microbiota between the disease and healthy groups. Notably, disease mortality varied consistently with the gradient of relative abundance of Proteobacteria (intestine, R2 = 0.46, p < 0.05) and Cyanobacteria (gill, R2 = 0.67, p < 0.01), indicating their potential use as diagnostic criteria. Furthermore, the elevated hepatosomatic index, NO3-N, COD and TC (sediment) were directly correlated with diseases (r > 0.54, p < 0.01). Mean concentrations of NO3-N, COD and TC were elevated by 78.87%, 25.63% and 44.2%, respectively, in ponds where diseases occurred. Quantitative analysis (qPCR) revealed that Aeromonas sobria infected hosts through a potential pathway of “sediment (4.4 × 105 copy number/g)-water (1.1 × 103 copy number/mL)-intestine (1.2 × 106 copy number/g)”. Similarly, the potential route for Aeromonas veronii was sediment (4.9 × 106 copy number/g) to gill (5.1 × 105 copy number/g). Additionally, the complexity of microbial networks in the intestine, water, and sediment was significantly lower in the disease group, although no similar phenomenon was observed in the gill microbial network. In summary, these findings reveal that elevated concentrations of crucial environmental factors disrupt the linkages within microbiota, fostering the growth of opportunistic bacteria capable of colonizing fish gut or gills. This offers new insights into potential mechanisms by which environmental factors cause disease in fish.

A new genus and a new species of microcotylids (Polyopisthocotyla, Platyhelminthes), gill parasite of the pink dentex Dentex gibbosus (Teleostei, Sparidae) off Tunisia and notes on Polyopisthocotyla and Monopisthocotyla from Dentex spp.

The study of the polyopisthocotylan parasites of marine fishes in the western Mediterranean is carried on using an integrative approach combining morphology and DNA barcodes. Ktarius patrickbrueli n. gen. n. sp (Polyopisthocotyla, Microcotylidae), from the gills of pink dentex Dentex gibbosus (Teleostei, Sparidae) from the western Mediterranean Sea off Tunisia, is described. Anatomical and morphological features of the new genus are described, and the molecular barcodes for nuclear and mitochondrial markers (28S rRNA and cox1) are generated. The new genus is closely related to Microcotyle by sharing a symmetrical haptor, inverted question mark-shaped ovary and unarmed vagina. However, Ktarius n. gen. can be distinguished from Microcotyle and other Microcotylinae taxa by an unarmed male copulatory organ, formed by a long muscular cirrus, a basal layer of concentric muscles, and an elongated thick-walled ejaculatory bulb. A partial 28S rDNA sequence of K. patrickbrueli n. gen. n. sp. was obtained and found to be distinct from all known microcotylid sequences, with a p-distance of 5–13%. A phylogenetic tree constructed from available microcotylid sequences revealed that K. patrickbrueli n. gen. n. sp. clustered in a strongly supported clade of Microcotylinae, containing species of Omanicotyle, Bivagina, and Microcotyle confirming its belonging to the Microcotylinae subfamily. The cox1 sequences of K. patrickbrueli n. gen. n. sp. were highly divergent from the closely related genus Pauciconfibula and confirmed its distinction. This new genus is the third polyopisthocotylan genus to be described from sparids of Dentex.

Ectoparasite infection levels differ between fish from upwelling-exposed and sheltered rocky reefs areas in Brazil

Ubiquitous and abundant within marine ecosystems, parasites play essential ecological roles such as shaping host population dynamics, altering competition between species, and influencing energy flows through communities. Their diversity and population dynamics are demonstrably shaped by both seasonal and geographic variations. These variations have been often explored at broad spatial scale. However, parasite communities can exhibit significant disparities even at small spatial scales, driven by factors such as wave exposure, temperature fluctuations, and benthic habitat composition. We investigated how crustacean parasites of fish – caligids and gnathiids - differed between two distinct habitats, which are separated solely by a few kilometres, at Arraial do Cabo, Brazil. These two habitats were characterised by a sheltered embayment (hereinafter referred to as “inside”) or an exposed upwelling habitat (hereinafter referred to as “outside”). Individual fish from four species were examined in both habitats. We found that the infestation rate of caligids varied among fish species and, gnathiids varied between the two sampling sites. Gnathiids were absent from fish outside, while they were present on fish inside the embayment. This disparity suggests a critical role of local environmental factors in shaping gnathiid distribution. Potential drivers include temperature fluctuations, substrate composition, and wave exposure, which differed markedly between the two sites. Conversely, caligid parasites infected fish in both locations. While environmental factors may also influence caligid abundance, they appear to exhibit greater tolerance compared to gnathiids. These findings emphasize the importance of incorporating fine-scale environmental heterogeneity when investigating parasite distribution patterns.

The impact of apple cider vinegar on nonalcoholic fatty liver disease in rainbow trout, Oncorhynchus mykiss: A study of therapeutic potential and health benefits

AbstractIn this study, we aimed to experimentally induce fatty liver disease in rainbow trout, Oncorhynchus mykiss, and then assessed the illness recovery process, growth, and changes in the expression of FAAH and ACADL genes in both healthy (0 [C2] and 4% apple cider vinegar [T4]) and diseased fish (0 [C1], 1 [T1], 2 [T2], and 4% [T3]) apple cider vinegar. To conduct the study, 180 rainbow trout were randomly assigned to six different experimental treatments, each with three replications. The investigation lasted for 60 days. Growth indices, liver histology, blood biochemical parameters, and transcription of the ACADL and FAAH genes in the liver tissue were measured. The study found no significant differences in the final weights across all the treatments. Apple cider vinegar (ACV) administration resulted in a decrease in AST, ALT, and ALP; however, these values did not show a significant difference from C2. In T3, triglycerides significantly decreased (p &lt; 0.05), whereas in T4, triglycerides significantly increased (p &lt; 0.05). Hepatocytes from ACV‐containing treatments showed reduced fat compared with T4 and the control group (C1). While there was a significant difference (p &lt; 0.05) in the expression of the FAAH gene, there was no significant difference (p &gt; 0.05) in the expression of the ACADL gene between experimental treatments. The findings of our study indicate that an inclusion of up to 2% ACV may have positive effects on trout aquaculture and NAFLD treatment.

Prevalence and Parasitological Examination of Fish Parasites in Clarias gariefinus from Selected Fish Farms in Sokoto Metropolis, Nigeria

Study’s Excerpt The prevalence of fish parasites in fish farms within the Sokoto metropolis is assessed. The results revealed high prevalence of Camallanus spp. and Capillaria spp. among fish populations. Water quality analysis revealed that there is interaction between physicochemical parameters and parasite prevalence. A comprehensive approach to fish farm management and disease control is provided. Full Abstract Fish are known to be affected by parasites both internally and externally with detrimental effects on fish growth and development. This study aimed to determine the prevalence of fish parasites in selected fish farms in the Sokoto metropolis. A total of one hundred and twenty fish samples were collected from ten selected fish farms and subjected to microscopic examination. Water samples were collected from ten fish farms and analysed using the standard procedures recommended by the American Public Health Association. The results indicate that 35.0% of the fish were infected with the parasite (P&lt;0.0300). Significant high prevalence of 50.0% and 48.1% was recorded in the gender and age groups of the fishes (P&lt;0.0308) and (P=0.0003), respectively. However, a significantly high prevalence of 47.6%, 49.1% and 31.7% was also observed in the length, weight, and body part of the fishes (P&lt;0.0.0000). This study identified two nematode species (Camallanus spp. and Capellaria spp.) with Camallanus spp. showing a higher prevalence of 60.3% was obtained in Camellanus spp. among the parasite species identified. The parameters such as pH, dissolved oxygen (DO) and nitrate (NO3) were assessed, and results were analysed using one-way analysis of variance (ANOVA) with the aid of SPSS version 27.0. The values of the physicochemical parameters were between the range of 6.68+0.11 to 7.83±0.05 for pH, 5.23+0.03 to 8.17±0.88 mg/L for DO, and 13.70+1.37 to 100.33+0.33 for NO3 respectively. All parameters examined were within acceptable limits recommended by the World Health Organization. Maintaining an optimum feeding strategy, regular monitoring of the water quality parameters and vaccinations will help to further decrease the rate of the parasite.

Mandarin Fish Ranavirus (MRV) Infection Induced Inflammation and Histologic Lesions in the Gut of Mandarin Fish.

Mandarin fish ranavirus (MRV) is widely spread in China and causes huge economic losses to the mandarin fish (Siniperca chuatsi) aquaculture. However, the pathogenesis of MRV is still unclear. In the present study, mandarin fish were artificially infected with MRV, and then different gut compartments from diseased fish were subjected to histologic analysis by H&E staining, quantification of proinflammatory genes and MRV copies by qPCR. MRV-MCP protein expression was assessed using indirect fluorescence assay (IFA) and immunohistochemistry. Proliferation of IgM+ B cells was evaluated by indirect fluorescence assay (IFA). Then, we found that MRV infection caused serious histologic lesions along with inflammatory cell infiltration, especially in the foregut. A significant accumulation of IgM+ B cells was detected in the foregut (~6.5-fold) and hindgut (~3.3-fold), respectively. The expression of inflammation-related genes such as IL-1β, IL-6, IL-8,TNF-α, CSF1r and NCF1 was significantly upregulated in the foregut, varying from ~2.8-fold to ~11.9-fold. In addition, MRV exhibited foregut tropism, according to the investigation of viral loads and MCP protein expression. Overall, our findings indicated that MRV-induced hyperinflammation in the gut eventually led to enteritis. This study provided new insights into uncovering the pathogenesis of MRV infection.

Lymphocystis viral disease impacts the diversity and functional profiles of the skin microbiome in gilthead seabream.

Lymphocystis viral disease (LVD) is a highly transmissible disease known to affect multiple fishes worldwide. Although this disease is usually benign, mortalities can occur in cases where infection is severe or secondary infection with bacterial pathogens and parasites occur. However, little is known about the bacterial dynamics of fish with LVD or what bacterial pathogens may be responsible for secondary infections. Here we assessed the effects of LVD on the skin microbiome of gilthead seabream by comparing 30 symptomatic, asymptomatic and recovered (three weeks after infection) fish using 16S rRNA high-throughput sequencing. Our results show that LVD is associated with significant changes in microbiome structure and function. Importantly, fish pathogens like Tenacibaculum maritimum and some Vibrio species increased their abundance. Moreover, microbial metabolic activities of the commensal microbiota that may confer some protection to fish were suppressed in diseased fish. After reducing fish cage density to treat symptoms and three weeks of recovery, the abundance of pathogens was significantly reduced and microbiome functionality was recovered, although community structure remained significantly different. These results show that LVD can severely disrupt the bacterial communities of the skin of the gilthead seabream, leading to an increase in bacterial pathogens responsible for relevant diseases in gilthead seabream farms.

A Fish Trematode Vitellibaculum Identified in the Gastrointestinal Tract of the Little Gull (Larus minutus): The First Report of Trematode from Iran

Vitellibaculum, which belong to the subfamily Megasoleninae within the family Haploporidae, are typically parasites of marine fish. This trematode has been reported from different regions of the world. The Little Gull (Larus minutus), a migratory bird common in the coastal regions of Iran, was the subject of this study. A dead bird found by the Environmental Protection Agency in Babolsar was referred to the laboratory of the Department of Parasitology of the Science and Research branch of the Islamic Azad University. After necropsy and sampling of the intestinal contents, a single trematode was identified. After staining and slide preparation, it was identified as Vitellibaculum and registered in the National Parasitology Museum of Tehran University.

Comparison and evaluation of DNA vaccines against Nocardia seriolae infection in largemouth bass (Micropterus salmoides)

Chronic granulomatous diseases caused by Nocardia seriolae have resulted in substantial economic losses for the aquaculture industry. DNA vaccines are considered a promising approach for controlling infectious diseases. To develop effective DNA vaccines against N. seriolae, we selected Ag85L, MmaA4, HspX, Rv3407, and HtpG as candidate antigens. Among these, pcDNA-Ag85L and pcDNA-MmaA4 were the most effective against N. seriolae infection in largemouth bass (Micropterus salmoides), achieving the highest relative percentage survival (RPS) rates of 78.6 % and 92.9 %, respectively. Tissue bacterial loads and histopathological tests revealed a significant reduction in bacterial abundance in the liver, spleen, head kidney, and trunk kidney of the immunised groups compared to that in the control group. Additionally, no distinct pathological changes were observed in the spleen or head kidney tissues. The expression levels of immune-related genes including IL-1β, IL-8, MHCI, MHCII, CD4, and CD8α were significantly upregulated in the pcDNA-Ag85L and pcDNA-MmaA4 immunised groups, thus indicating that the two DNA vaccines mediated immune protection by promoting both humoral and cellular immune responses. Overall, the pcDNA-Ag85L and pcDNA-MmaA4 DNA vaccines demonstrated strong potential for protecting largemouth bass against N. seriolae infection, offering an innovative solution for controlling granulomatous diseases in fish.

Lactococcus garvieae as a Novel Pathogen in Cultured Pufferfish (Takifugu obscurus) in China

In October 2023, a disease outbreak in pufferfish (Takifugu obscurus) farms in Zhongshan City, Guangdong, China, caused high mortality. Diseased fish (mean length: 15 ± 1 cm) exhibited swimming disorders, fin rot, hemorrhage, and an enlarged spleen. Histopathological observations generally revealed inflammation, necrosis, and congestion in the spleen, kidneys, and brain tissues. The most severe pathological changes included interstitial edema and tubular atrophy in the kidneys, hemosiderin deposition in the spleen, massive red blood cell infiltration, and a decrease in lymphocytes. A single strain of bacteria (Tol-1) was isolated from the diseased pufferfish and identified as a Gram-positive streptococcus strain, exhibiting α-hemolysis on sheep blood agar plates. Through biochemical characterization, 16S rDNA sequencing, morphological analysis, and specific primer-based identification, the Tol-1 strain was identified as Lactococcus garvieae, serotype I. Antimicrobial susceptibility testing indicated that Tol-1 was sensitive to Chloramphenicol, Ampicillin, Cephalexin, and Doxycycline, but resistant to Kanamycin, Gentamicin and Ciprofloxacin. In addition, 15 common virulence factors were detected in the Tol-1 strain, including adhPav, adhPsaA, adhC I–II, adh, and hly 1–3. Pufferfish (mean length: 17 ± 1 cm) subjected to artificial infection via intraperitoneal injection (IP) with the Tol-1 strain exhibited clinical symptoms and histopathological damage similar to those observed in naturally infected fish. An infection dose of 1 × 105 CFU/fish resulted in 80% mortality. The study fulfilled Koch’s postulates, indicating that the disease outbreak in pufferfish was caused by L. garvieae, which exhibited a high mortality rate in pufferfish despite the subtle clinical symptoms. These results serve as a warning for pufferfish farming areas and provide a scientific basis for future prevention and control efforts.

Curcumin is an efficacious therapeutic agent against Chilodonella uncinata via interaction with tubulin alpha chain as protein target

Chilodonella, a parasitic ciliate that infects both cold water and warm water fish, can impede the growth of juvenile fish and cause considerable economic losses globally to freshwater aquaculture. In this study, the parasite was collected from both the gills and zygotes of largemouth bass (Micropterus salmoides). Isolated from diseased fish, the parasites were identified as Chilodonella uncinata based on morphological features and genetical diagnostic characterization using the partial small subunit ribosomal RNA gene. To develop an effective approach to treat chilodonellosis caused by C. uncinata in largemouth bass farming, we first developed an in vivo culture model for propagating C. uncinate and thus could use for morphological characterization, molecular analyses and antiparasitic drug screening. Curcumin was successfully identified as an efficacious anti-C. uncinata agent from 26 phytochemical compounds. When administered at a concentration of 6 mg/L, curcumin not only completely cured infected largemouth bass but also shielded uninfected fish from C. uncinata infections. The 24 h median effective concentration (EC50) of curcumin against C. uncinata was 3.098 mg/L. Remarkably, the 96 h median lethal concentration (LC50) of curcumin against largemouth bass was determined to be 17.143 mg/L, approximately 5.533 times higher than EC50. The mechanism of action of curcumin was investigated by the cellular thermal shift assay, demonstrating that tubulin alpha chain was the binding target for curcumin. Moreover, SEM investigations further provided morphological evidence suggesting that curcumin induces parasite demise by disrupting the parasite's body surface and subsequently infiltrating its interior. These findings collectively emphasize the potential of curcumin as a safe and effective therapeutic agent for controlling C. uncinata in aquaculture.

Nanopore-based full-length transcriptome sequencing of the skin in Pseudopleuronectes yokohamae identifies novel antimicrobial peptide genes

The marbled flounder (Pseudopleuronectes yokohamae) is highly esteemed for its exceptional nutritional value and delicious taste. However, this species has extremely limited transcriptome data, which can offer priceless information for disease protection. In the study, the skin transcriptomic sequencing of P. yokohamae revealed 7.72 GB of clean data using the Nanopore sequencing platform. The results revealed 30,498 transcripts of functional annotations in the P. yokohamae transcriptome. All transcripts were searched in eight functional databases. A total of 10,337 ORFs were obtained, of which 6081 complete ORFs accounted for 58.83% of all predicted CDS. Moreover, 10,195 SSRs were detected. Meanwhile, the non-pecific immunity pathways were investigated for better understanding of the immunological reaction in P. yokohamae, and seven innate immune pathways were identified. The innate-immune related genes were highly expressed in the NOD-like receptor signaling pathway, followed by the C-type lectin receptor signaling pathway, Toll-like receptor signaling pathway, RIG-I-like receptor signaling pathway and Cytosolic DNA-sensing pathway. In this study, four families of antimicrobial peptides (AMPs) in P. yokohamae were analysed for the first time, including piscidins, hepcidins, liver-expressed antimicrobial peptide and defensins. Seven AMPs, including Pypleurocidin-like WF3, Pypleurocidin-like WFX, Pyhepcidin 1, Pyhepcidin-like 1, PyLEAP-2, Pybeta-defensin and Pybeta-defensin-like 1, were further identified. The seven AMPs showed a highly identity in their cDNA and genomic structures and an inducible expression pattern preferable to skin in response to pathogens. The transcriptomic data and investigation of AMPs from P. yokohamae promote a deeper awareness of fish mucosal immunity and provide information in the prevention of fish diseases.

Spatial distribution of bacterial communities driven by environmental factors in the sediment of Lateolabrax japonicus ponds

Dynamic changes of bacterial communities in the sediment are very important for preventing diseases and water quality in aquaculture ponds. In this study, bacterial communities in the sediment of Sea perch Lateolabrax japonicus, an important farmed fish in China, ponds were studied using 16S rRNA Illumina sequencing and functional gene array. At the phylum level, Pseudomonadota, Actinomycetota and Chloroflexota were the dominant species. The bacterial community composition was different in spatial variation. Among the environmental factors, the concentration of nitrogen related factors (TN, NO3−-N NH3-N, NO2−N) and total organic carbon was the main impact on the composition of bacterial community, especially denitrifying bacterial community. Nitrifying and denitrifying bacteria accounted for 4.81 %, and bacteria related to nitrogen cycle accounted for 18.36 %. Higher diversity of bacteria in healthy fish pond than that of the diseased fish pond. In the diseased fish pond, lower abundance of Nitrosospira and higher abundance of Nitrobacter were found, and the contents of NH3-N, NO2−-N and total organic carbon were significantly higher. This study would help to reveal that microbial community structure could reflect the health of cultured animal and surroundings, and it could provide a theoretical reference for the healthy environments in the sediment of Sea perch ponds in South China.