High Fish Mortality Research Articles

The therapeutic role of Azadirachta indica leaves ethanolic extract against detrimental effects of Aeromonas veronii infection in Nile tilapia, Oreochromis niloticus.

Bacterial pathogens cause high fish mortalities and in turn economic losses in fish farms. Innovative strategies should be applied to control bacterial infections instead of antibiotics to avoid the resistance problem. Consequently, the present investigation studied the curative potential of Azadirachta indica leave ethanolic extract (AILEE) on Aeromonas veronii infection in Oreochromis niloticus. A preliminary trial was assessed to evaluate the curative dose of AILEE which was found to be 2.5mg/L. One hundred and sixty fish were divided into equal four groups in four replications, where group 1 and group 2 were non-challenged and treated with 0- and 2.5-mg/L AILEE, respectively. Group 3 and group 4 were challenged with A. veronii and treated with 0- and 2.5-mg/L AILEE, respectively for 10days. A. veronii infection produced severe clinical manifestations and a high mortality rate in the infected fish. Furthermore, the infected fish exhibited a significant rise in the hepatorenal indices (aspartate aminotransferase, alanine aminotransferase, and creatinine), the oxidant biomarker (malondialdehyde), and the stress indicators (glucose and cortisol). A significant reduction in the protein profile and antioxidant/immune parameters (catalase, immunoglobulin M, lysozyme, nitric oxide, and phagocytic activity) was observed in the infected fish. Water application of the infected group to 2.5-mg/L AILEE notably ameliorated the hepatorenal indices, the oxidant biomarker, and the stress indicators. Furthermore, AILEE improved the antioxidant/immune indices. Water application of 2.5-mg/L AILEE could be useful against A. veronii infection in O. niloticus culture.

Hematological and Histological Analysis of Tilapia (Oreochromis Niloticus) Cultured in Floating Net Cages After Disease Outbreak

Recently, Tilapia fish cultivated in floating net cages in Karang Intan District experienced a sudden death from June 4 to June 5. At some point, mortality reached 50% of the population in floating net cages. The purpose of this study was to analyze the hemtology and histology of tilapia (Oreochromis niloticus) after exposure to disease outbreaks that were cultivated in floating net cages. The research location was carried out at the Laboratory of Fish Pests and Diseases, Faculty of Fisheries and Maritime Affairs, University of Lambung Mangkurat. The animal samples used were tilapia showing clinical symptoms of sick fish obtained from floating net cages in Mali-Mali Village, Karang Intan District, which experienced quite high fish mortality cases and 3 fish were taken. Based on the results of hemtological analysis of tilapia (Oreochromis niloticus) after being exposed to disease outbreaks which were cultivated in floating net cages, the hemoglobin levels of tilapia obtained in this study ranged from 6.9-7.8 g/dl, the average hematocrit of tilapia was obtained in this study has a range between 37.2 - 58.9%, the average tilapia leukocrit obtained in this study has a range between 2.89 - 6.61% and blood plasma is a liquid component of blood consisting of 99% water and 8-9% protein.

Exosomes derived from olive flounders infected with Streptococcus parauberis: Proteomic analysis, immunomodulation, and disease resistance capacity

Multidrug-resistant Streptococcus parauberis causes high fish mortality in aquaculture, necessitating an urgent need for innovative control strategies. This study aimed to develop an immunizing agent against S. parauberis using exosomes isolated from the plasma of olive flounders infected experimentally with S. parauberis (Sp-Exo). Initially, we tested the in vitro immunomodulatory effect of Sp-Exo in murine macrophage RAW264.7 cells and compared it to that of exosomes isolated from naïve fish (PBS-Exo-treated). Notably, Sp-Exo treatment significantly (p < 0.05) upregulated pro-and anti-inflammatory cytokines (Il1β, Tnfα, and Il10), antimicrobial peptide, defensin isoforms (Def-rs2 and Def-ps1), and antiviral (Ifnβ1 and Isg15) genes. In vivo studies in larval and adult zebrafish revealed similar patterns of immunomodulation. Furthermore, larval and adult zebrafish exhibited significantly (p < 0.05) enhanced resistance to S. parauberis infection following treatment with Sp-Exo compared to that with PBS-Exo. Proteomic analysis using isobaric tags for relative and absolute quantitation (iTRAQ) approach revealed the presence of 77 upregulated and 94 downregulated differentially expressed proteins (DEPs) in Sp-Exo, with 22 and 37 significantly (p < 0.05) upregulated and downregulated DEPs, respectively. Gene Ontology, Kyoto Encyclopedia of Genes and Genomes, and Search Tool for the Retrieval of Interacting Genes/Proteins analyses revealed that these genes are associated with key pathways, such as innate immune responses, complement system, acute phase responses, phospholipid efflux, and chylomicron remodeling. In conclusion, Sp-Exo demonstrated superior immunomodulatory activity and significant resistance against S. parauberis infection relative to that on treatment with PBS-Exo. Proteomic analysis further verified that most DEPs in Sp-Exo were associated with immune induction or modulation. These findings highlight the potential of Sp-Exo as a promising vaccine candidate against S. parauberis and other bacterial infections in olive flounder.

Deciphering the impact of endoparasitic infection on immune response and gut microbial composition of Channa punctata.

Intestinal parasitic infections caused by helminths are globally distributed and are a major cause of morbidity worldwide. Parasites may modulate the virulence, gut microbiota diversity and host responses during infection. Despite numerous works, little is known about the complex interaction between parasites and the gut microbiota. In the present study, the complex interplay between parasites and the gut microbiota was investigated. A total of 12 bacterial strains across four major families, including Enterobacteriaceae, Morganellaceae, Flavobacteriaceae, and Pseudomonadaceae, were isolated from Channa punctata, infected with the nematode species Aporcella sp., Axonchium sp., Tylencholaimus mirabilis, and Dioctophyme renale. The findings revealed that nematode infection shaped the fish gut bacterial microbiota and significantly affected their virulence levels. Nematode-infected fish bacterial isolates are more likely to be pathogenic, with elevated hemolytic activity and biofilm formation, causing high fish mortality. In contrast, isolates recovered further from non-parasitised C. punctata were observed to be non-pathogenic and had negligible hemolytic activity and biofilm formation. Antibiogram analysis of the bacterial isolates revealed a disproportionately high percentage of bacteria that were either marginally or multidrug resistant, suggesting that parasitic infection-induced stress modulates the gut microenvironment and enables colonization by antibiotic-resistant strains. This isolation-based study provides an avenue to unravel the influence of parasitic infection on gut bacterial characteristics, which is valuable for understanding the infection mechanism and designing further studies aimed at optimizing treatment strategies. In addition, the cultured isolates can supplement future gut microbiome studies by providing wet lab specimens to compare (meta)genomic information discovered within the gut microenvironment of fish.

Rapid and efficient inactivation of viruses in seawater by LIG electrodes

Water-borne viral diseases are a significant concern for public health. In particular, they threaten the health of people and animals in countries that lack proper water treatment facilities. Novel water treatment technology may efficiently improve water quality and prevent the spread of waterborne viral pathogens. Laser-induced graphene (LIG) has been shown to inactivate viruses and bacteria with its photothermal properties, electrochemical reaction, and rough surface texture. However, LIG's activity to prevent virus transmission via contaminated water has not been fully explored. Here, we demonstrated that enveloped and non-enveloped viruses in seawater could be rapidly inactivated by LIG technology. After being activated by 3 V of electricity, the LIG electrodes inactivated both types of viruses spiked in water within 30 min. In addition, the electrolyzed seawater exhibited virucidal effects even after the cessation of the electrical charge. The generation of different oxidants, such as chlorine, chlorine dioxide, and hydrogen peroxide, may play an essential role in the antiviral mechanism of the LIG electrodes. Furthermore, after 10 min of electrolysis, the pH of the seawater dropped from approximately 8–5, which may also have contributed to the virucidal effects of the LIG technology. The virucidal activity of LIG technology highlighted its potential for preventing the spread of viral infections via seawater systems which may have public health implications in areas where seawater is used in the sewage system. It may also have applications in aquaculture, where viral diseases do not have treatments and can cause high fish mortality.

Testing the antibacterial effectiveness of mangosteen peel extract (Garcinia mangostana L) against Aeromonas hydrophila Bacterial infection in dumbo catfish (Clarias gariepinus)

Plants belonging to the Clusiaceae species are Garcinia mangostana Linn (mangosteen fruit). The skin layer of this fruit has been used as a traditional medicine for wound healing, topical infections. Mangosteen rind contains compounds including mangostin, mangostenol, mangostinon A, mangostenon B, trapezifolixanthone, tovofillin B, alpha mangostin, beta mangostin, garsinon B, mangostanol, flavonoids, epicatechin. Gartanin, gamma mangostin, garsinon E, epicatechin. Farming African catfish (Clarias Gariepinus) when facing serious problems such as fish are susceptible to disease, mainly due to bacteria. One type of bacteria that causes the disease is Aeromonas hydrophila. This type of bacteria can cause high fish mortality in African catfish (Clarias Gariepinus) of various sizes. The purpose of this study was to determine the effect of mangosteen rind extraction on the growth of Aeromonas hydrophila bacteria in vitro, as well as the 96-hour Lethal Dose (LD50) value of mangosteen rind extract after exposure to African catfish (Clarias Gariepinus). In this study, the antibacterial activity of the material was tested in vitro with concentrations of 0%, 1.56%, 3.125%, 6.25%, 12.5%, 25% and 50%.

Immune protection and safety of Aeromonas veronii fliD deletion mutant as a live attenuated vaccine in Cyprinus carpio

Aeromonas veronii is one of the important pathogens causing motile Aeromonas septicemia (MAS) in aquaculture, leading to high fish mortality and severe economic losses. Live attenuated vaccines are considered to be an effective method to control bacterial infections and have been widely used in veterinary vaccines. In order to develop a safe and effective vaccine against MAS, the safety and protective efficacy of the fliD gene deletion strain of A. veronii as a live attenuated vaccine for Cyprinus carpio were evaluated in this study. After intraperitoneal injection vaccination, the A. veronii ΔfliD was able to colonize temporarily in the head kidney and spleen, and was finally cleared by C. carpio without causing clinical symptoms and affecting the growth performance of C. carpio. The significantly increased IgM levels in the serum indicated that both intraperitoneal injection and immersion vaccination induced a significant humoral immune response. The pro-inflammatory factors IL-1β, TNF-α and IL-6 were significantly increased at the early stage after intraperitoneal injection vaccination, indicating that A. veronii ΔfliD induced an inflammatory response in C. carpio, which facilitated bacterial clearance. In addition, a significant proliferation of head kidney lymphocytes was also observed after stimulation with A. veronii soluble antigen. The survival rates of C. carpio vaccinated by intraperitoneal injection and immersion were 83.33% and 56.67% after intraperitoneal challenge with wild-type A. veronii, compared with 13.33% and 16.67% in the control group. The histopathological examination showed that A. veronii ΔfliD could protect the liver and spleen against tissue lesion after challenge. These results indicate that attenuated strain A. veronii ΔfliD can induce an effective humoral and cellular immune response and provide protection against A. veronii for C. carpio without adverse effects, which can be developed as an effective live attenuated vaccine candidate to control the A. veronii infection.

Determining Factors and Zootechnical Output of Biosecurity Practices in Fish Farms in the Wouri Division, Cameroon.

Biosecurity practice limits the occurrence of diseases and economic losses in fish farms. The objective of this study was to characterize fish farming in the Administrative Division of Wouri, Cameroon (3°97'04″-3°58'13″N; 9°76'78″-9°46'4.3″E) and assess the biosecurity practices. A cross-sectional biosecurity audit was then conducted in 33 fish farms from March to May 2022. The "snow ball" technique, on-farm observations, and face-to-face interviews of farm managers using a semistructured questionnaire were used for data collection. The results showed that most of the fish farmers were between 18 and 40 years of age (63.64%) and not trained in fish farming (60.61%). The lack of finance (57.57%) was the main constraint to the biosecurity practice. The high fish mortality rate (>15%) was recorded in 66% of the farms. Overall, the compliance rate (CR = 40.52 ± 14.70%) and adoption rate (AR = 40.40 ± 30.10%) of biosecurity measures were intermediate. No type C farm or at the minor risk level of contamination was recorded. Farmers of 18 to 40 years of age (45.24 ± 14.75%) who attended higher school (43.83 ± 14.44%) and received training in fish farming (47.44 ± 14.39%) recorded a significant higher CR. The CR and AR were significantly higher for the isolation component (CR = 60.17 ± 19.81%; AR = 60.17 ± 25.68%) followed by traffic control (CR = 53.53 ± 25.87%; AR = 53.53% ± 34.86) and sanitation (CR = 27.70 ± 19.70%; AR = 29.84 ± 26.00%). A strong (R 2 = 0.725), positive, and significant (p=0.019) linear relationship was found between the level of education of fish farmers and the biosecurity compliance rate while the health status of fish was weakly (R 2 = 0.207), positively, and significantly (p=0.017) influenced by the compliance rate. Fish farming is an income-generating activity that still requires socioeconomic, technical, and institutional efforts for optimal productivity. The Cameroonian government should emphasize on the education, training, and capacity building of farmers on biosecurity practices to minimise the introduction, establishment, and spread of diseases.

Effects of antibiotics on Vietnam koi, Anabas testudineus, exposed to Aeromonas dhakensis as a co-infection

The dietary effects of antibiotics on aquatic disease is circumstantial and has not been investigated under infections. the efficacy of erythromycin, after 10 days in use and 10 days off, on the survival and infection rate of (Anabas testudineus) after co-infection with antibiotic-resistant Aeromonas dhakensis (isolate NV5M or V7L). The mortality rate observed in non-medicated groups of co-infected fish (93.3 and 100%) was significantly higher (p < 0.05) than that in the medicated group of naturally infected fish (NIF) (53.3%) but not significantly different to that in medicated groups of co-infected fish (66.6% and 86.6%). In particular, the loads of invasive erythromycin-resistant bacteria (ERB) were markedly higher (p < 0.05, 3.5–4.8 times) in the kidney of co-infected fish medicated for 5 days than those in NIF. The measure of ERB in the kidney of fish co-infected with isolate V7L, whether medicated or not for 10 days, was significantly higher (p < 0.05) than that in non-medicated NIF and also that in the medicated group of fish co-infected with isolate NV5M. In addition to the elevation of gut-derived ERB invasion and colonization in the kidney, synergistic effects of the competition between mixed pathogens caused by co-infection and medication might result in a high fish mortality rate. Further investigation of antibiograms and/or new strategies for aquatic disease control should be undertaken with mixed infections and interaction of pathogens to achieve the optimal treatment effect.

Omics Strategies in Current Advancements of Infectious Fish Disease Management.

Simple SummaryThe increasing demand for fish products has caused disease-related problems due to intense fish practices in fish farms. The fish diseases infection caused by bacteria, viruses, and parasites could lead to high fish mortality that affected the aquaculture industry. Recently, a systematic strategy to overcome fish disease problems using multi-omics platforms has been used to provide a better understanding of how to improve the resistance of fish to pathogen infection. In this review, we highlight the current multi-omics strategies such as transcriptomics, proteomics, and metabolomics to provide information regarding their molecular mechanisms of action, subsequently important in discovering potential biomarkers for various infectious fish diseases in the aquaculture system.Aquaculture is an important industry globally as it remains one of the significant alternatives of animal protein source supplies for humankind. Yet, the progression of this industry is being dampened by the increasing rate of fish mortality, mainly the outbreak of infectious diseases. Consequently, the regress in aquaculture ultimately results in the economy of multiple countries being affected due to the decline of product yields and marketability. By 2025, aquaculture is expected to contribute approximately 57% of fish consumption worldwide. Without a strategic approach to curb infectious diseases, the increasing demands of the aquaculture industry may not be sustainable and hence contributing to the over-fishing of wild fish. Recently, a new holistic approach that utilizes multi-omics platforms including transcriptomics, proteomics, and metabolomics is unraveling the intricate molecular mechanisms of host-pathogen interaction. This approach aims to provide a better understanding of how to improve the resistance of host species. However, no comprehensive review has been published on multi-omics strategies in deciphering fish disease etiology and molecular regulation. Most publications have only covered particular omics and no constructive reviews on various omics findings across fish species, particularly on their immune systems, have been described elsewhere. Our previous publication reviewed the integration of omics application for understanding the mechanism of fish immune response due to microbial infection. Hence, this review provides a thorough compilation of current advancements in omics strategies for fish disease management in the aquaculture industry. The discovery of biomarkers in various fish diseases and their potential advancement to complement the recent progress in combatting fish disease is also discussed in this review.

Assessment of Sparus aurata (Gilthead Seabream) stock in Bardawil lagoon, southeast Mediterranean Sea

During present study period from October 2020 to April 2021, gilthead seabream Sparus aurata stock was estimated by using many assessment models to evaluate actual status on Bardawil lagoon. Length at first capture (Lc) was 17.10 and 16.70 cm for females and males respectively, but it was 16.9 cm for all individuals that corresponding age at first capture (tc= 2.49 year). Length at first recruit Lr was 10.70 and 9.70 cm for females and males, respectively, corresponding age tr= 0.77 year. The length at first maturity was Lm= 18.18 cm that corresponding age tm= 2.85 years. Virtual population analysis shows some of intensive capture on S. aurata at its early life’s. Yield per recruit and biomass per recruit tend to collapse as a result of high fishing mortalities. The current study concludes an exact overfishing pressure of S. aurata stock in Bardawil lagoon.

Immune response of silver pomfret (Pampus argenteus) to Amyloodinium ocellatum infection.

Amyloodinium ocellatum (AO) infection in silver pomfret (Pampus argenteus) causes extensive mortality. Insufficient information exists on the molecular immune response of silver pomfret to AO infestation, so herein we simulated the process of silver pomfret being infected by AO. Translucent trophosomes were observed on the gills of AO-infected fish. Transcriptome profiling was performed to investigate the effects of AO infection on the gill, kidney complex and spleen. Overall, 404,412,298 clean reads were obtained, assembling into 96,341 unigenes, which were annotated against public databases. In total, 2730 differentially expressed genes were detected, and few energy- and immune-related genes were further assessed using RT-qPCR. Moreover, activities of three immune-related (SOD, AKP and ACP) and three energy-related (PKM, LDH and GCK) enzymes were determined. AO infection activated the immune system and increased interleukin-1 beta and immunoglobulin M heavy chain levels. Besides, the PPAR signalling pathway was highly enriched, which played a role in improving immunity and maintaining homeostasis. AO infection also caused dyspnoea, leading to extensive lactic acid accumulation, potentially contributing towards a strong immune response in the host. Our data improved our understanding regarding the immune response mechanisms through which fish coped with parasitic infections and may help prevent high fish mortality in aquaculture.

An investigation into the pathogenesis of blue catfish alloherpesvirus in ictalurid catfish

AbstractIntensive aquaculture production systems often encounter infectious viral disease outbreaks causing substantial fish mortalities and associated economic losses. Blue catfish alloherpesvirus (BCAHV) is an Ictalurid herpesvirus with limited information on pathogenesis. To determine the host‐specificity and potential host range of BCAHV, the virus was inoculated onto various fish cell lines belonging to families Ictaluridae, Cyprinidae, Centrarchidae, and Clariidae. Viral replication and exhibition of cytopathic effects (CPEs) were restricted to cell lines from the family Ictaluridae indicating the host preference of BCAHV. Subsequently, fish challenges were conducted to evaluate intrinsic and extrinsic factors influencing BCAHV infection. Mortality because of BCAHV infection was significantly higher in blue catfish and least in channel catfish further specifying the host preference of the virus. Histopathological assessment of the BCAHV infected fish revealed splenitis with severe erythrophagia. Host susceptibility to BCAHV differed with age with fish at 60 days post hatch being more susceptible. Temperature had a significant role in the activation and pathogenesis of BCAHV. Fish exposed to BCAHV at a sustained high temperature had significantly low mortality suggesting the likelihood of virus inactivation. Virus exposure in tanks with high stocking density resulted in significantly high fish mortalities indicating horizontal transmission is a key element in BCAHV pathogenesis. The heightened pathogenicity of BCAHV in blue and hybrid catfish as observed in this study validates its potential to be a significant pathogen in catfish production.

An update on the ornamental fish industry in Malaysia: Aeromonas hydrophila-associated disease and its treatment control

Malaysia is the world’s major producer and exporter of ornamental fish, contributing 9% to the global trade and taking the second position after Singapore. Because of their artistic appeal and tremendous commercial value for international trade, ornamental fish recently gain rapid importance for foreign exchange and as a source of employment. While ornamental fish production is growing, there is an increase in infectious diseases, resulting in high fish mortality with significant economic loss. Bacterial disease is a serious problem for ornamental fish industry. Bacterial species surveillance in diseased freshwater ornamental fish from an aquarium shop reveals that Aeromonas hydrophila is the most dominant bacteria isolated. Consequently, Malaysia is stepping up its efforts by implementing the Economic Transformation Program and other biosecurity steps to address the aquaculture issues and encourage the regrowth of the ornamental fish market. Chemotherapeutic medications, phytobiotics, probiotics, yeast extracts, vaccines, and disinfectants can be used in controlling bacteria. Further studies should be done to find new antibacterial agents from natural sources to combat bacterial fish diseases and reduce fish mortality rate in sustainable aquaculture farms. This review summarizes the literature on ornamental fish industries and aquaculture production in relation to A. hydrophila-associated diseases and ornamental fish health management in Malaysia.

Isolation, Identification and Antimicrobial profile of Aeromonas spp., Pseudomonas spp. and Vibrio spp. from the Nile Tilapia, Oreochromis niloticus in fish farms

Nile tilapia (Oreochromis niloticus) aquaculture represents one of the most important cultivation species in Egypt. However, Tilapia farming encounters some problems that result in high fish mortalities and huge economic losses due to bacterial pathogens. Thus, the current study aimed to isolate, identify, and characterize the pathogenic bacteria affecting Nile tilapia farming in El-Abbassa, Abo-Hammad, Sharkia. Besides, antibiotic susceptibility to pathogens was determined as a primary step for controlling diseases. Hence, a collection of 252 fish samples was gathered from 200 fish farms. Upon microbiological and biochemical analysis, the presence of only 3 bacterial genera was detected, including Gram-negative bacteria of Aeromonas spp. (52.80 %), Pseudomonas spp. (27.9 %), and Vibrio spp. (19.3 %). Aeromonas sobria showed the highest prevalence in the infected Oreochromis niloticus. Antibiogram test revealed high levels of resistance expressed by all bacterial isolates to Ampicillin, Amoxicillin, and Erythromycin. On the other hand, Norfloxacin was effective against all isolated bacteria followed by Ciprofloxacin. Establishing effective control methods for pathogenic bacteria would greatly enhance fish production.

Transcriptome and 16S rRNA analyses revealed differences in the responses of largemouth bass (Micropterus salmoides) to early Aeromonas hydrophila infection and immunization

The largemouth bass (Micropterus salmoides) is an economically important fish species, but disease caused by Aeromonas hydrophila has led to the high mortality of this fish in farming environments. However, few studies have focused on the differences in the responses of largemouth bass to infection and immunization with A. hydrophila. In the present study, we found high fish mortality after A. hydrophila infection but not after immunization. Then, the immune response difference of largemouth bass in early infection and immunization with A. hydrophila was analyzed using transcriptome profiling and 16S rRNA sequencing. The results from the transcriptome analysis revealed that many upregulated genes were enriched in metabolic pathways after infection and immunization, but the number of upregulated genes associated with metabolic pathways and the magnitude of their upregulated expression in the infection group were much greater than they were in the immunization group, suggesting that A. hydrophila infection might cause metabolic disorders in largemouth bass. Increases in pro-inflammatory cytokine levels and reduced expression of genes associated with adaptive immunity were also observed in the infection group. Moreover, the results of the 16S rRNA analysis revealed that the intestinal microbiota homeostasis of the largemouth bass was severely disrupted by A. hydrophila infection but not by immunization. These results collectively demonstrated that metabolic disorders, higher inflammation, a reduced adaptive immune response and disrupted microbiota homeostasis in early infection might be important factors for the high mortality of largemouth bass caused by A. hydrophila infection.

A study of acute toxicity of newly synthesized compound on adult hydrobiont Danio rerio

From ancient times the people used different poisons as a treatment for diseases of different genesis. To date, almost nothing has changed. One of the main conditions for the development of a new drug is its low toxicity. Literature analysis has shown that 1,2,4-triazole-3-thione derivatives are low-toxic compounds and exhibit a wide range of pharmacological activities.&#x0D; The aim of this work was the investigate acute toxicity LC50 in vivo of sodium 2-((4-amino-5-(thiophen-2-ylmethyl)-4H-1,2,4-triazole-3-yl)thio)acetate on the Zebrafish (Danio rerio) aquatic model according to OECD instruction № 203.&#x0D; Materials and methods. Determination of acute toxicity LC50 of the test compound was performed in vivo on a model of the aquatic organism Zebrafish (Danio rerio) according to the instruction OECD № 203 (Fish, Acute Toxicity Test) for testing chemical compounds (acute toxicity test on fish from 10.12.2009).&#x0D; It was used fish 2 months of age, 11.8 ± 0.1 mm long, and weighing 2.6 ± 0.2 g in the experiment. The concentration of the test compound ranged from 5.0 mg/l to 100.0 mg/l. Test water-soluble compounds were dissolved in distilled water. Each mini-aquarium with a certain dose of the compound contained at least 7 individuals of Danio rerio. During the experiments, the fish were kept on a diet for a test 96 hours and their mortality was checked every 24, 48, 72 and 96 hours. Statistical analysis of the results was performed using the program Statistica 6.&#x0D; Results. According to the obtained data, graphs of the dependence of the concentration on the fish mortality percentage were constructed. Then the corresponding values of LC50 sodium 2-((4-amino-5-(thiophen-2-ylmethyl)-4H-1,2,4-triazole-3-yl)thio)acetate were calculated.&#x0D; According to the acute toxicity of LC50 (96 hours) of sodium 2-((4-amino-5-(thiophen-2-ylmethyl)-4H-1,2,4-triazole-3-yl)thio)acetate, which according to the classification of D. R. Passino and co-authors allowed it to be classified as a moderately toxic compound.&#x0D; Conclusions. The acute toxicity LC50 in vivo of sodium 2-((4-amino-5-(thiophen-2-ylmethyl)-4H-1,2,4-triazole-3-yl)thio)acetate on the Zebrafish (Danio rerio) aquatic model was investigated. The research was conducted in accordance with the national “General Ethical Principles of Animal Experimentation” approved by the First National Congress on Bioethics and the “Bioethical Expertise of Preclinical and Other Animal Research”.&#x0D; The highest fish mortality occurs on the last day of observation (96 hours). The highest number of Zebrafish deaths is at a minimum concentration of the substance. The acute toxicity LC50 (96 hours) of the test substance was 4.5364 mg/l.

Peracetic acid treatment of Ichthyophthirius multifiliis (Ciliophora: Ichthyophthiriidae) and Trichodina spp. reduces the infection by Aeromonas hydrophila and improves survival in Nile tilapia (Oreochromis niloticus)

Co-infections with ectoparasites and bacteria commonly occur in fish farms and are associated with high mortality. In March 2020, a private Nile tilapia (Oreochromus niloticus) farm in Sharkia Governorate, Egypt, experienced high fish mortality, and the clinically diseased fish were characterized by lethargy, abnormal swimming behavior, loss of appetite, skin hemorrhages, exophthalmia, and abdominal distension. Laboratory parasitological and bacteriological examinations of the diseased fish revealed concurrent infections with Ichthyophthirius multifiliis, Trichodina centrostrigeata, and Aeromonas hydrophila. Pathological findings indicated severe gill and skin infections with I. multifiliis and T. centrostrigeata associated with necrosis, hemorrhages, and depletion of the hemopoietic organs, as well as cardiac inflammation. Peracetic acid (PAA) was applied as a strong oxidizing antimicrobial disinfectant, and in vitro evaluation showed that 5 ppm achieved 5-log reductions in the viable colony count of A. hydrophila after a contact time of 5 min and 1.076 ppm represented the 4-h 50% lethal concentration (LC50) for the infective stage of I. multifiliis (theronts). The continuous exposure of culture water to 1 mg L−1 PAA for 1 week followed by periodical use of PAA at the same concentration twice per week was effective in eradicating the ciliated protozoans, reducing the aerobic bacterial density in water, ameliorating the pathological alterations, restoring the fish health, and reducing the mortality rate by up to 15%. Thus, the use of PAA to treat I. multifiliis and T. centrostrigeata reduces the infection by A. hydrophila in Nile tilapia and improves their survivability.

Prediction of fish mortality based on a probabilistic anomaly detection approach for recirculating aquaculture system facilities.

Aquaculture is a fundamental sector of the food industry nowadays. However, to become a sustainable and more profitable industry, it is necessary to monitor several associated parameters, such as temperature, salinity, ammonia, potential of hydrogen, nitrogen dioxide, bromine, among others. Their regular and simultaneous monitoring is expected to predict and avoid catastrophes, such as abnormal fish mortality rates. In this paper, we propose a novel anomaly detection approach for the early prediction of high fish mortality based on a multivariate Gaussian probability model. The goal of this approach is to determine the correlation between the number of daily registered physicochemical parameters of the fish tank water and the fish mortality. The proposed machine learning model was fitted with data from the weaning and pre-fattening phases of Senegalese sole (Solea senegalensis) collected over 2018, 2019, and 2020. This approach is suitable for real-time tracking and successful prediction of up to 80% of the high fish mortality rates. To the best of our knowledge, the proposed anomaly detection approach is the first time studied and applied in the framework of the aquaculture industry.

APPLICATION OF COMPARATIVE GENOME IN AQUACULTURE DISEASES DIAGNOSIS

The sustainability of aquaculture industry is critical both for global food security and economic welfare. However, the massive wealth of pathogenic bacteria poses a key challenge to the development of a sustainable bio-control method. Recent advances in genome sequencing study combined with pan-genome analysis can be an efficacious management applied to numerous aquatic pathogens. Thus, routine comparative genome analyses of aquatic pathogens will deduce the phylogenomic diversity and possible evolutionary trendsof aquatic bacterial pathogen strains, elucidate the mechanisms of pathogenesis, as well as estimate patterns of pathogen transmission across epidemiological scales. This study also reviews comparative pan-genome analysis with a particular focus on controlling aquatic diseases, especially for: (i) re-identifying the previously misidentified strain with high accuracy and discovering novel isolates that may be associated with high rateof fish mortalities, (ii) developing routine pan-PCR based on highly informative identified genetic targets that are capable of distinguishing all the clinical isolates, and finally (iii) studying the multivalent vaccine following reverse vaccinology towards the prevention of numerous aquatic animal diseases.