The transmission of aflatoxins from fish products to consumers primarily occurs through the contamination of fish flesh and feed by aflatoxigenic fungi. This study comprehensively examined the prevalence and extent of fungal contamination in the flesh of Oreochromis niloticus and Mugil cephalus, as well as in fish feed. Furthermore, it assessed the aflatoxin-producing potential of Aspergillus flavus through fluorometric and molecular assays, providing critical insights into the risks associated with mycotoxin contamination in aquaculture products. O. niloticus and M. cephalus (n = 20 for each species) and fish feed (n = 30) were collected from fish farms and feed markets in Ismailia Governorate, Egypt. The total mold counts exceeded the permissible limit in 25

THIS manuscript detailed an investigation into parasitic and bacterial co-infections that caused significant morbidity and mortality in farmed thin-lipped grey mullet (Liza ramada) and keeled mullet (Liza carinata) populations. Examination revealed heavy infestations of the copepod parasite Caligus clemensi in the buccal cavity, gills, and skin. Morphological identification of C. clemensi was confirmed through genetic analysis using 18S rRNA sequencing and phylogenetic analysis. The postmortem examinations revealed internal signs of disease, including liver enlargement, hemorrhages, and ascites, while histopathology demonstrated severe destruction of gill tissues associated with the parasite infection. Bacterial cultures isolated Vibrio parahaemolyticus as the cause of secondary bacterial infections, which was further characterized phenotypically and identified through recA gene sequencing. Concerningly, high rates of antibiotic resistance were detected among the V. parahaemolyticus isolates. Therapeutic prolonged baths with Virocid (R) disinfectant followed by probiotic treatment with Sanolife Pro-W (R) effectively cleared the parasite infections, resolved secondary bacterial infections, and improved fish survival rates. In summary, heavy parasite burdens of C. clemensi coupled with multiple antibiotic-resistant V. parahaemolyticus infections, were identified as the primary causes of mullet mortalities. The integrated therapy effectively managed aquaculture outbreaks, providing an alternative to excessive chemical pesticides or antibiotics by eliminating parasitic infestations and controlling secondary vibriosis.

This study investigated a disease outbreak characterized by caligid copepod infestations and subsequent secondary bacterial infections in European seabass (Dicentrarchus labrax) and flathead grey mullet (Mugil cephalus) cultivated at a private facility in the Deeba Triangle region of Egypt. Moribund fish displayed brown spots on the skin, tongue, and gills, along with lethargy and excess mucus. The fish suffered severe infections, exhibiting external hemorrhages, ulcers, and ascites. The fish had pale, enlarged livers with hemorrhaging. Comprehensive parasitological, bacteriological, molecular, immunity and histopathological analyses were conducted to identify the etiological agents and pathological changes. Caligid copepod infestation was observed in wet mounts from the buccal and branchial cavities of all examined fish, and the caligids were identified as Caligus clemensi through COI gene sequencing and phylogenetic analysis. Vibrio alginolyticus was confirmed as a secondary bacterial infection through biochemical tests, recA gene sequencing, and phylogenetic analyses. Antibiotic susceptibility testing revealed resistance to β-lactams, aminoglycosides, and trimethoprim-sulfamethoxazole in V. alginolyticus isolates. Upregulation of the inflammatory marker IL-1β in gill and skin tissues indicated a robust cell-mediated immune response against the pathogens. Histopathological examination revealed severe tissue damage, hyperplasia, hemorrhage, and congestion in the gills, along with hepatocellular degeneration and steatosis in the liver, providing initial insights into this outbreak. A comprehensive therapeutic regimen was implemented, comprising prolonged hydrogen peroxide immersion baths, followed by the application of the nature-identical plant-based compound Lice-less and probiotic Sanolife Pro-W supplementation. This integrated approach effectively eliminated C. clemensi infestations, controlled secondary bacterial infections, and restored fish health, reducing morbidity and mortality rates to minimal levels.

The aquaculture industry is suffering from significant financial setbacks due to an increasing frequency of disease outbreaks, posing a threat to the sector’s sustainability. Various bacterial, viral, parasitic, and fungal pathogens have led to massive mortalities in farmed fish worldwide. Throughout the years, the management of fish diseases has predominantly centered around the utilization of conventional antibiotics and chemicals. Nevertheless, their indiscriminate use has given rise to serious implications, including an increase in resistant pathogens, disruptions in the metabolic processes of fish, degradation of the aquatic environment, the presence of drug residues in aquatic products, and a potential threat to human health. Various effective bio-based and immunoprophylaxis alternative therapies have been developed to overcome these impediments. Recent alternative therapeutic approaches to fish diseases encompass a range of strategies, including phytotherapeutics, nanotherapeutics, probiotics, prebiotics, synbiotics, phage therapy, vaccination, quorum quenching, antimicrobial peptides, biosurfactants, bacteriocins, stem cells, and diagnostic-based therapy. Advancements in biotechnology have significantly enhanced the efficacy of these therapies. However, additional research is essential to refine the utilization of these therapeutic approaches. Critical concerns, such as efficacy, cost, risks, availability, and adverse effects on fish and the ecosystem, need to be addressed to establish guidelines for their sustainable application in aquaculture. This review will increase aquaculturists’ awareness of recent therapies used in fish farming, their mechanisms, challenges, and impacts while promoting the sustainability of commercial aquaculture.

This study aimed to conduct a multidisciplinary investigation integrating detailed morphology, molecular characterization, water parameters, histopathology alteration, and the trials of treatment of Clinostomum spp. In this study, 300 Nile tilapia (Oreochromis niloticus) were collected from the farmed and wild Nile River at Al Bahr Al Aazam, Giza Governorate to assess Clinostomid infection prevalence. Fish and water samples were collected from private fish farms, and water drains at Dakahlia, and Giza, Egypt. Analysis of the water revealed inadequate water quality, particularly in the fish farms. Snails and piscivorous birds were abundant at fish collection sites. The recovered Clinostomid MCs morphological characteristics and COI gene sequence analysis identified them as Clinostomum complanatum, C. phalacrocoracis, and Euclinostomum heterostomum. Clinostomid MCs disturbed the fish’s hematological and biochemical blood parameters. Bath treatment of parasitized fish with praziquantel (2 mg/L for 24 h) revealed a significant reduction in the number of vital MCs vs. infected fish (non-treated). Praziquantel (PZQ) is an effective and safe therapy for controlling Clinostomid infections affecting farmed Nile tilapia. The current findings indicate a link between poor environmental conditions and Clinostomum infections in tilapia. The study highlights the impacts of Clinostomid MCs on fish health and recommends bath treatment with PZQ as an efficient control method for these dangerous parasites to protect human and fish health.

DIGENETIC trematode infections pose a significant threat to the African catfish aquaculture industry in Egypt. This study investigated the prevalence, morphological characteristics, molecular composition, and host responses to Prohemistomum vivax encysted metacercariae (EMC) infecting farmed African catfish (Clarias gariepinus). A total of 160 fish were collected from farms in Kafr-elsheikh Governorate between 2022 and 2023. Parasitological examination revealed an overall prevalence of 55% (n = 88) of infection with EMC of P. vivax. The prevalence of infection exhibited seasonal variations, with the highest rates in summer (100%), followed by spring (75%), autumn (30%), and winter (15%). Parasitic intensity showed significant major seasonal differences, with the lowest mean intensity in winter (1.6 +/- 2.3 EMC per field) and the highest in summer (14.4 +/- 9.3 EMC per field). Molecular sequencing and phylogenetic analysis of the internal transcribed spacer 2 (ITS2) gene unambiguously identified the metacercariae as P. vivax, overcoming limitations of traditional morphology-based techniques that cannot differentiate between digenean species when present as encysted stages. Histopathological examination revealed the presence of multiple parasitic cysts between hepatocytes, with diffuse vacuolar degeneration of hepatocytes. Muscles showed the presence of multiple parasitic cysts embedded in muscle bundles, with observed tissue reaction, inflammatory cell infiltration, oedema of interstitial tissue, and hyaline degeneration of muscle fibers. These findings highlight the importance of implementing effective control strategies to minimize the impact of P. vivax EMC infection on the Egyptian catfish aquaculture industry.

Motile aeromonads were identified in earthen-pond-farmed Oreochromis niloticus that suffered massive mortalities in Egypt during the summer of 2020. The fish showed hemorrhagic septicemic signs. Poor management practices and inadequate water quality measures were observed in the affected earthen ponds. Motile aeromonads (n = 31 isolates) were identified from 70 fish specimens. Based on their phenotypic and molecular characteristics, isolates were identified as: Aeromonas hydrophila (n = 12), A. veronii (n = 10), A. caviae (n = 5), and A. sobria (n = 4). Bacteriological examination of farm water samples also revealed aeromonads (n=9) and some fish-nonpathogenic bacteria. The aeromonad isolates recovered from fish exhibited lipase (52.5%) and protease (47.5%) activities and harboured some virulence genes: Ser (62.5%), Aer (55%), ela (37.5%), gcaT (32.5%), Hyl (25%), laf-A (22.5%), and Act (20%). They also harboured numerous antibiotic-resistance genes, including aadA (37.5%), tetC (32.5%), tetA (27.5%), sul 1 (20%), and blaTEM (10%). Virulence and antibiotic resistance genes were also noted in some of the Aeromonas spp. isolates obtained from farm water. Aeromonads were highly resistant to ampicillin, amoxicillin, and gentamicin but highly susceptible to ciprofloxacin and florfenicol antibiotics. Aeromonas spp pathogenicity was confirmed by the experimental infection of Oreochromis niloticus. Our results indicate a positive correlation between excessive tilapia mortalities, motile Aeromonas septicemia and adverse water quality parameters measured during the summer. This study provides data on the virulence, pathogenicity, and antibiotic resistance of motile aeromonads affecting fish and humans, which will be useful for developing efficient therapies.

Motile aeromonads, and Cyathocotylidaespp.co-infections were identified in farmed Nile tilapia(Oreochromis niloticus) which suffering from mortalities. Moribund fish showed signs of septicemia, skin irritations, and res-piratory distress. A total of 150 O. niloticus specimens showing signs of disease were collected from the affected earthmen ponds and examined. Bacteriological examination of fish samples revealed infections with motile aeromonads species. Phenotypic characteristics and phylogenetic analysis of gyrB gene sequences of aeromonads isolates identified them as Aeromonas hydrophila (12.6%), A.sobria (12.6%), and A. caviae (30.4%). Aeromonads strains harbored some virulence genes: Aer (78.62%); Hyl (60.86%); laf-A (52.17%); and Act (47.82%). The antibiogram of aeromonads showed high resistance against tetracycline (73.9%), and gentamycin (65.2%), while a high sensitivity was noticed to ciprofloxacin (82.6%),and trimethoprim/sulfamethoxazole (60.86%). Parasi-tological examination of fish revealed the presence of Cyathocotylidae spp. encysted metacercaria (EMC). High levels of interleukin 6 (IL-6) and cluster of differentiation 4 (CD4) were noticed in fish with parasitic and bac-terial co-infection compared to those with a single infection or non-infected. Experimentally infected fish with Aeromonas spp. showed septicemic signs similar to that noticed in naturally infected tilapia with variable cu-mulative mortality. The study is one of the earlier reports identifying as Cyathocotylidae spp., and motile aero-monads co-infections, and their link with the exaggerated tilapia mortality which will be of value for incorporating these pathogens in the necessary management strategies to protect fish health.

Rapid and accurate detection of bacterial pathogens is critical in controlling disease outbreaks affecting farmed fish. The present study aimed to develop a novel serological diagnostic approach using nano‑silver based Enzyme-linked immunosorbent assay (ELISA) for speedy detection of Aeromonas veronii infections in Nile tilapia. A. veronii isolates used in ELISA assays were recovered from moribund Nile tilapia during a disease outbreak in a private fish farm in Egypt. A. veronii isolates were identified based on alignment analysis of the gyrB and 16S rRNA gene sequences. A. veronii antisera used in ELISA assays were prepared in tilapia, and the bacterial antigens were formalin-killed. The cut-off values were 0.46 and 0.48 in traditional and nano-based ELISA. There were no cross-reactions with bacterial isolates (Aeromonas hydrophila, Aeromonas caviae, Aeromonas sobria, Pseudomonas fluorescens, and Vibrio vulnificus). The lowest antigen concentration that produced positive results after checkerboard titration in indirect-ELISA (i-ELISA) and dot ELISA was 15 μg and 250 ng of prepared antigen, respectively. Nano-ELISA and nano-based dot-ELISA antigen concentration was 10 μg and 100 ng, respectively. Sera concentration was 1:100 in indirect-ELISA and dot-ELISA, while it was 1:50 in nano-based ELISA and nano dot-ELISA. The i-ELISA successfully detected anti-Aeromonas IgG antibodies with 83.33% sensitivity and 66.67% specificity, while in the dot-ELISA, the sensitivity and specificity were 83.33% and 100%, respectively. Nano dot-ELISA had 100% sensitivity, specificity, and accuracy. Nano dot-ELISA assays have higher specificity, sensitivity, and accuracy than traditional ELISAs in detecting A. veronii. Further studies are needed to develop a rapid test kit for on-site field diagnosis.

Columnaris is a common flavobacterial disease affecting tilapia aquaculture. Flavobacterium columnare has been identified as being responsible for the heavy mortalities of earthen-pond-cultured Nile tilapia (Oreochromis niloticus) at the Fayoum Governorate, Egypt. Mortalities have been closely associated with bad husbandry in the overstocked ponds. Diseased fish showed fin and tail rot with a thick yellowish turbid mucus covering the affected skin and gills. Scanning electron microscopy revealed the presence of numerous bacterial cells dispersed in the affected gill tissues. Most of the investigated specimens (60%) were infected with F. columnare. Forty-seven bacterial isolates were phenotypically identified based on cultural and biochemical characteristics. Molecular identification, virulence property assessment, and antibiotic-sensitivity testing were performed on 10 randomly selected isolates. The identities of the isolates were confirmed by gene sequence and phylogenetic analyses. These isolates yielded variable results regarding virulence genes (gtf, norB, and trx) and ability to adhere to fish gills. All isolates exhibited proteolytic and chondroitin lyase activities but had different antibiotic-sensitivity profiles. The pathogenicity of one highly pathogenic isolate was tested via intramuscular injection into juvenile O. niloticus. The challenged fish showed fin rot and skin ulceration with 80% cumulative mortalities. The study discussed critical points in the pathogenesis of columnaris disease affecting Nile tilapia that may help to find out effective control measures and refers to the need for prudent use of antimicrobials in aquaculture to protect aquatic animals and human health.

Marine pollution and bacterial disease outbreaks are two closely related dilemmas that impact marine fish production from fisheries and mariculture. Oil, heavy metals, agrochemicals, sewage, medical wastes, plastics, algal blooms, atmospheric pollutants, mariculture-related pollutants, as well as thermal and noise pollution are the most threatening marine pollutants. The release of these pollutants into the marine aquatic environment leads to significant ecological degradation and a range of non-infectious disorders in fish. Marine pollutants trigger numerous fish bacterial diseases by increasing microbial multiplication in the aquatic environment and suppressing fish immune defense mechanisms. The greater part of these microorganisms is naturally occurring in the aquatic environment. Most disease outbreaks are caused by opportunistic bacterial agents that attack stressed fish. Some infections are more serious and occur in the absence of environmental stressors. Gram-negative bacteria are the most frequent causes of these epizootics, while gram-positive bacterial agents rank second on the critical pathogens list. Vibrio spp., Photobacterium damselae subsp. Piscicida, Tenacibaculum maritimum, Edwardsiella spp., Streptococcus spp., Renibacterium salmoninarum, Pseudomonas spp., Aeromonas spp., and Mycobacterium spp. Are the most dangerous pathogens that attack fish in polluted marine aquatic environments. Effective management strategies and stringent regulations are required to prevent or mitigate the impacts of marine pollutants on aquatic animal health. This review will increase stakeholder awareness about marine pollutants and their impacts on aquatic animal health. It will support competent authorities in developing effective management strategies to mitigate marine pollution, promote the sustainability of commercial marine fisheries, and protect aquatic animal health.

Antibiotic-resistant Aeromonas veronii isolates (4) were identified from moribund Oreochromis niloticus by phenotypic and genotypic characterization using 16S rDNA gene sequence analysis. Antibacterial efficacy of silver nanoparticles (AgNPs) was assessed in vitro and in vivo against A. veronii isolates. A minimum inhibitory concentration (MIC) and 48 h lethal concentration 50% (LC50) for AgNPs were estimated to be 3.125 mu g/ml and 8.77 mg/L respectively. Four hundred fifty fish were divided into 10 groups in triplicate (15/replica). Two control groups were untreated with AgNPs: The first (G1) was not infected, whereas the second (G2) was experimentally infected with A. veronii. AgNPs were added to aquarium water with fish either noninfected (G3-G6) or infected (G7-G10) with A. veronii. AgNPs concentrations were 100, 250, 500 and 750 mu g/L, respectively, for both sets of fish groups. Fish infected with A. veronii but untreated with AgNPs showed septicaemic symptoms, a high mortality rate (71%) and poorer haematological parameters (red blood cells [RBCs], haemoglobin concentration [Hb], hematocrit [HCT%], mean cell volume [MCV] and mean cell haemoglobin [MCH]); impaired nonspecific immune responses (total protein, albumin, globulin and lysozymes); reduced antioxidant capacity (catalase [CAT], peroxidase and superoxide dismutase [SOD]); a significant increase in creatinine, uric acid, alanine aminotransferase (ALT), aspartate aminotransferase (AST) and alkaline phosphatase (ALP); and genotoxic effects in gills. Treatment with AgNPs increased fish survival; improved haematological, immunological and antioxidant activities; and optimized liver and kidney function. The most favourable outcome was seen using an AgNPs concentration of 750 mu g/L. Various histopathological changes were found among experimental fish.

The present study investigated the protective effects of dietary Allium cepa against Saprolegnia parasitica infections and the amelioration of cadmium-induced immunosuppression in Oreochromis niloticus . Saprolegnia isolates were recovered during an outbreak of saprolegniasis in farmed O. niloticus raised in a poor aquatic environment . Isolates were identified phenotypically as S. parasitica. Results were confirmed further by ITS gene sequencing. Four fish groups were kept in water with cadmium (1.5 mg/L) and fed for 30 days on a diet supplemented with crude or alcoholic extracts of A. cepa using two concentrations (0.5% or 1%). Positive (with Cd) and negative (without Cd) control fish groups were given the basal diet. The 96 h LC 50 value of Cd in tilapia was (15.1 mg/L Cd). Fish exposed to Cd showed poor growth performance parameters, abnormal biochemical measurements, impaired immunological responses, and high oxidative stress indicators. Feeding tilapia on A. cepa- supplemented diets enhanced their growth performance (WG, SGR) and improved the nonspecific immune responses (WBCs, total protein, globulins, lysozyme, myeloperoxidase, and antiproteases). The inclusion of A. cepa in the diets reduced the oxidative stress (GST, SOD) and significantly decreased fish mortality after the challenge with S. parasitica . Dietary supplementation with A. cepa reduced cadmium accumulation in fish organs and up-regulated IL-1β and IFNɣ levels. The most favorable benefits were obtained by the addition of 0.5% A. cepa extract. Our results highlight the immunostimulatory properties of A. cepa dietary supplementation for farmed tilapia and recommend its use prophylactically to control saprolegniasis and mitigate cadmium adverse effects.

Edwardsiellosis is a serious bacterial disease affecting Nile tilapia (Oreochromis niloticus), causing septicemia and mortalities. Edwardsiella tarda and Edwardsiella anguillarum were isolated from Nile tilapia summer mortality events in Egypt. Diseased fish showed hemorrhagic septicemia, skin erosions, and eye opacity. A total of 24 Edwardsiella spp. isolates were retrieved from the investigated fish specimens. Phenotypic and biochemical characteristics grouped isolates into typical Ed. tarda (n = 14 strains) and atypical Ed. tarda (n = 10 strains). The BLAST analysis of sodB gene sequencing confirmed the conventional identification of typical Ed. tarda strains (n = 14) and reidentified all the atypical strains (n = 10) as Ed. anguillarum. Isolates showed a combination of virulence factors, including biofilm formation (66.6%), hemolysis (100%), chondroitinase (50%), and proteolytic activity (20.8%). The major part of isolates showed high resistance to ampicillin, amoxicillin, gentamycin antibiotics and harbored tetA, blaCTX-M, and aadA1 resistance genes. Pathogenicity testing of isolates in O. niloticus confirmed their virulence. Challenged fish exhibited septicemic signs similar to naturally diseased fish. Infections in naturally infected tilapia triggered acute and chronic histopathological alterations. Degenerative and necrotic changes were noticed in hematopoietic organs. Granulomas were noticed in between the hepatic parenchyma. The data extracted from the study confirm that accurate identification of the causative agents of edwardsiellosis should be reliant on genetic-based approaches. Analysis of the bacterium virulence properties offers insights into establishing novel therapeutics for edwardsiellosis control. The findings refer to the need for antimicrobial sensitivity testing to minimize antimicrobial resistance and increase therapy efficacy.

Dactylogyrus extensus and Pseudomonas fluorescens are serious pathogens in Cyprinus carpio aquaculture causing severe impacts and substantial economic losses. During the early spring of 2021, abnormal mortalities were reported among farmed C. carpio. Moribund fish showed anorexia, respiratory distress, dermal ulcers, and septicemia. The water analysis revealed low dissolved oxygen (3.4 mg/L), and high un-ionized ammonia levels (0.65 mg/L). Seventy moribund C. carpio specimens were collected and subjected to parasitological and bacteriological examinations. The monogenetic trematode D. extensus was discovered in wet mounts from the gills of all the examined fish samples (100%). The identity of recovered parasites was confirmed by sequencing and alignment of the 28S rDNA gene. P. fluorescens was concurrently identified in the infested fish samples (58.5%) based on phenotypic characteristics using the API20 E. The identity of bacterial isolates was confirmed further by sequencing and alignment of 16S rRNA gene. The IL-1β and MHCII were upregulated in infested fish in tandem with the severity of infections. P. fluorescens isolates displayed high resistance to most of the tested antibiotics. The study is one of the earlier reports on D. extensus and P. fluorescens co-infections in farmed C. carpio and highlights the need of effective control programs to protect fish health and minimize losses.

Amyloodiniosis and vibriosis are serious diseases in European seabass (Dicentrarchus labrax) hatcheries with noticeable high mortality. This study was conducted on tank-cultured D. labrax frys at a private marine hatchery near Mariout Lake (Alexandria, Egypt). Frys showed a high mortality rate (70%), lethargy, darkening, asphyxia, ascites, and velvety skin appearance. Both infectious agents were presumptively identified in all investigated frys. The identities of the two recovered agents were confirmed by molecular assay and phylogenetic analysis. On the tissue level, histopathological examination of skin, splenic, and renal tissue indicated severe alterations due to the direct impacts of both infections. On the cellular level, scanning electron micrographs showed both protozoal and bacterial pathogens on/in gill epithelial cells in solitary and colonial forms. Vibrio alginolyticus showed variable results for tested antibiotics, with a higher sensitivity to florfenicol. A successful control strategy was strictly adopted to overcome infections and stop mortalities. Copper sulphate and hydrogen peroxide were efficiently applied to tank water to overcome A. ocellatum infections. Further, florfenicol was effectively used to overcome systemic V. alginolyticus infections. The efficacy of treatments was confirmed by the absence of infectious agents in randomly collected fish samples. To the best of the authors' knowledge, this study is one of the earliest Egyptian studies that dealt with the dilemma of mass kills associated with external parasitic/systemic bacterial infections among hatchery-reared European seabass.

Egypt is the world's ninth-largest fish producer with a total production of 1.5 billion tons per year, and farmed fishes comprise almost 79.6% of the total production. Massive mortalities in market-sized farmed fish (freshwater and marine species) were documented all over fish farms in Egypt leading to serious economic losses. The poor biosecurity practices and awareness among smallholder fish farmers accompanied with a long period of temperature fluctuation may predispose farmed fish to be simultaneously coinfected with multiple pathogens. Moribund fishes usually exhibited various septicemic clinical signs and post-mortem lesions indicating that one or more septicemic bacterial pathogens were involved in these outbreak reports. Therefore, rapid and accurate identification of pathogens in the asymptomatic fish population is important for preventing the occurrence of infectious diseases and protecting consumers from seafoodborne illnesses. Molecular techniques provide sensitive, quick, and accurate data for identifying specific pathogens without the need for time-consuming traditional techniques. In addition, the development of cost-effective molecular techniques facilitates their wide implementation in routine clinical diagnostic approaches. Molecular diagnostic methods are useful for simultaneously identifying multiple bacterial pathogens that were challenging to recognize by commercial biochemical techniques. Genetic testing procedures could determine the genetic diversity between closely related strains at the subspecies level. Consequently, these techniques are required for the development of detecting methods for specific strains and for epidemiological investigations in bacterial diseases. This review documented a variety of molecular techniques, including amplification of nucleic acids, polymerase chain reaction (PCR), nested PCR, real-time PCR, multiplex PCR, loop-mediated isothermal amplification (LAMP), DNA microarrays, and nucleotide sequencing assays, that are commonly used to identify fish pathogens.

In recent years, Egyptian tilapia aquaculture has experienced mortality episodes during the summer months. The causative agents responsible for such mortalities have not been clearly identified. A total of 400 fish specimens were collected from affected tilapia farms within five Egyptian governorates. A total of 344 bacterial isolates were identified from the examined fish specimens. Bacterial isolates were grouped into seven genera based on API 20E results. The most prevalent pathogens were Aeromonas spp. (42%), Vibrio spp. (21%), and Streptococcus agalactiae (14.5%). Other emerging infections like, Plesiomonas shigelloides (10%), Staphyloccocus spp. (8%), Pseudomonas oryzihabitans, and Acinetobacter lwoffii (2.3%) were also detected. Sequence analysis of the 16S ribosomal RNA bacterial gene of some isolates, confirmed the phenotypic identification results. The analysis of antibiotic resistance genes revealed the presence of aac(6')-Ib-cr (35.7%), blaCTX gene (23.8%), qnrS (19%), ampC (16.7%), floR (14.3%), sul1, tetA, and van.C1 (2.4%) genes in some isolates. The antimicrobia resistance gene, qac was reported in 46% of screened isolates. Bacterial strains showed variable virulence genes profiles. Aeromonas spp. harboured (act, gcat, aerA, lip, fla, and ser) genes. All Vibrio spp. possessed the hlyA gene, while cylE, hylB, and lmb genes, were detected in S. agalactiae strains. Our findings point to the possible role of the identified bacterial pathogens in tilapia summer mortality syndrome and highlight the risk of the irresponsible use of antibiotics on antimicrobial resistance in aquaculture.

This study aimed to identify the mortality present in private fish farm Amyloodinium ocellatum and Cryptocaryon irritans were isolated from this outbreak affecting Liza carinata fingerlings at an earthen-based aquaculture facility in Damietta , Egypt. A total of 140 moribunds, L. carinata, were collected from the fish ponds during the mortality events. Physico-chemical analysis of water was analyzed. The skin, fins, gills, and eyes of each fish specimen were scraped gently onto slides in areas over 2 cm area. All smears were examined separately under the light microscope. Molecular identification of the parasites using analysis of ITS rDNA regions flanking both 18S and 28S rDNA genes of Amyloodinium protozoa and C. irritans . Identities of the detected parasites were confirmed by gene sequence and phylogenetic analysis. The majority of the examined fish (90%) were infected, 66.42% had a mixed infection, and 23.57% had a single infection either with A. ocellatum (10.71%) or C. irritans (12.85%).The mean intensity of A. ocellatum was 16.5 ± 2.03 in the skin and 13.18 ± 1.90 in the gills of infected fish, while that of C. irritans was 4.75 ± 1.05 in gills and 7.43 ± 1.45 in the skin, respectively. To control the emergent mortalities, affected ponds were treated using copper sulfate pentahydrate, hydrogen peroxides solutions, and amprolium hydrochloride powder in feed. Fish across the treated ponds were gradually improved with low morbidity and mortalityrates during the treatment period. The clinical disease was almost diminished at the end of the second week of treatment. Coinciding with the clinical improvement of the treated juveniles, microscopical examination of skin/gill scraps exhibited a marked decline in the number of protozoan parasites at the end of the second week of treatment.