Amr Fadel

Monogenean infections are one of the most economically important parasitic constraints in marine aquaculture; however, knowledge remains limited regarding their genetic diversity, epidemiology, and sustainable management strategies. This study investigated the prevalence, morphomolecular characterization, environmental drivers, and eco-friendly control of naturally occurring monogenean infections in European sea bass ( Dicentrarchus labrax ) from two marine farms along the Egyptian Mediterranean coast between February and May 2024. Infected fish exhibited respiratory distress, skin darkening, anorexia, and progressive emaciation under heavy infestation. Examination of gill smears identified an elongate-oval monogenean exhibiting morphological features consistent with D. laubieri . Phylogenetic analysis of partial 18 S rRNA gene sequences placed the specimen within the Diplectanum clade, corroborating its taxonomic affiliation (GenBank accession no. PZ253293.1). Parasitological indices varied significantly between farms, with a higher prevalence recorded at Farm 2 (75.00 ± 6.87%) than at Farm 1 (65.56 ± 7.51%) ( p < 0.05). Seasonally, the highest prevalence occurred in February, followed by a decline in April and a slight increase in May. Water quality analysis indicated a progressive rise in temperature on both farms, reaching 25.40 ± 0.16 °C in May. In contrast, Farm 2 was characterized by higher salinity, pH, and total ammonia levels, together with lower dissolved oxygen concentrations. Correlation analysis demonstrated a strong negative association between parasite prevalence and water temperature ( r = − 0.736, p < 0.05), whereas no significant correlations were observed with salinity, pH, dissolved oxygen, or total ammonia. In trials of treating the affected fish and based on toxicity testing, the safe exposure threshold for Y. schidigera extract was established at 150–200 µg/L, while fenbendazole exhibited a safe exposure limit of 20 µg/L. The experimental cohabitation successfully reproduced the infection, achieving a prevalence of 90% by day 14. Comparative therapeutic efficacy trials demonstrated the superior performance of Y. schidigera relative to fenbendazole under the present study conditions, with parasite reduction rates of 80.4% and 68.5%, respectively, accompanied by a lower incidence of mortality. Collectively, these findings highlight the combined influence of environmental conditions on monogenean infection dynamics and support phytogenic-based Y. schidigera as a promising eco-friendly alternative for parasite control in marine aquaculture systems.

Isopod taxonomy and ecological correlation are the primary challenges constraining control strategies for fish. 600 Egyptian sole ( Solea aegyptiaca ) and water samples were collected regularly across the three sectors of Qarun Lake in 2024. An in-depth morphological description of the collected free-swimming and attached isopods identified Livoneca redmanii Leach, 1818. Identification was confirmed by the close evolutionary relationship of L . redmanii isolates among the three sectors, as evidenced by sequencing and phylogenetic analysis of COI and 16S rRNA genes. Sequence data from both genes were deposited in GenBank, each with a unique assigned accession number. The utility of COI as a robust barcode for Cymothoidae, in contrast to the more conserved 16S rRNA, was further supported, aligning with best practices for species-level resolution. Isopod-infested fish exhibited respiratory distress, skin erosion, hemorrhagic patches, branchial damage, morbidity, and mortality. The highest prevalence rate of isopod was recorded in the west sector (82.5%), with the summer showing the highest prevalence across all three sectors. The west sector also exhibited the highest mean infestation intensity of 3.6 isopods per fish, compared to 1.8 and 2.6 isopods per fish in the middle and east sectors, respectively. A higher fish condition factor of 1.01 was reported in the middle sector, while lower values of 0.85 and 0.61 were observed in the east and west sectors, respectively. Physicochemical water analysis revealed elevated pH, total ammonia, salinity, turbidity, and lower dissolved oxygen, particularly in the west sector during the summer. The current study provided a detailed morpho-molecular description of L . redmanii in the Egyptian sole, along with spatial and temporal prevalence correlated to ecological factors. These findings emphasize the importance of implementing efficient control protocols that target these destructive invasive isopods.

This study characterized the bacterial pathogen associated with summer mortality in cultured Nile tilapia (Oreochromis niloticus) between June and August 2024 across two different farms. As well as, the autochthonous probiotic was isolated as a preventive strategy. Phenotypic characteristics identified Aeromonas veronii and confirmed by molecular sequencing of the gyrB gene. Total prevalence was higher in farm 1 (65.19%) than in farm 2 (51.11%), with respective mortality rates of 38.84% and 25.25%. Prevalence rates peaked in August, which was correlated significantly (P ≤ 0.05) with elevated water temperature, pH, ammonia, and salinity. Clinical signs included erratic swimming, skin hemorrhages, and corneal opacity, with necropsy including ascitic fluids, friable liver, and splenomegaly. Challenge assay confirmed LD50 of 2.7 × 10⁷ CFU/mL A. veronii and 66.67% cumulative mortality. Histopathological alterations showed intermuscular edema, glomerular atrophy of the kidneys, vacuolar degeneration of the liver, spleen necrosis, and hemosiderosis of intestinal tissues. A. veronii showed resistance to ampicillin, tigecycline, fosfomycin, and sulfamethoxazole-trimethoprim. To control Aeromonas infection, 18 autochthonous probiotic isolates were obtained from the healthy O. niloticus gut and identified as Bacillus paralicheniformis through phenotypic analysis and 16S rRNA gene sequencing. These probiotic isolates demonstrated strong antagonistic activity against the pathogenic A. veronii, ecto-enzymatic producing activities, and high bile salt tolerance. After comprehensive screening, seven Bacillus strains met safety criteria, exhibiting high sensitivity to antimicrobials, non-hemolytic activity, and non-pathogenic in the challenge test. This study confirms A. veronii as the causative agent of tilapia summer mortality and presents promising autochthonous probiotics for preventive strategies in aquaculture.

This study evaluated the effects of dietary supplementation with herbal extracts from Artemisia herba-alba, Lonicera japonica, and Lilium candidum on growth performance, survival, feed utilization, antioxidant capacity, and immune response in Litopenaeus vannamei. The efficacy of these herbal-supplemented diets was assessed in enhancing resistance against Vibrio parahaemolyticus-induced Acute Hepatopancreatic Necrosis Disease (Vp _AHPND). A total of 2,400 shrimp post-larvae (initial weight 0.74 ± 0.02 g) were randomly assigned to four triplicate groups. Shrimp were fed isonitrogenous and isocaloric diets: T1 (control, basal diet), T2 (basal diet + 250 mg/kg A. herba-alba), T3 (basal diet + 250 mg/kg L. japonica), and T4 (basal diet + 250 mg/kg L. candidum). Herbal-supplemented groups showed significantly improved ( _P ≤ 0.05) growth performance, feed utilization, and survival rates compared to the control, with T4 exhibiting the highest values. Significant enhancements of immune assays were observed in total hemocyte count, phagocytosis activity, total protein, glutathione peroxidase, and lysozyme activity in herbal-supplemented groups. Antioxidant indicators (catalase, superoxide dismutase, and phenoloxidase) were boosted while malondialdehyde levels decreased in herbal-treated shrimp. Following V. parahaemolyticus challenge, herbal diets effectively reduced cumulative mortality in L. vannamei. Histopathological examination revealed milder AHPND-associated alterations in A. herba-alba and L. candidum-treated groups, contrasting with atrophy, necrosis, and epithelial cell sloughing observed in the positive control. These findings demonstrate the immunostimulatory potential of A. herba-alba, L. japonica, and L. candidum as dietary supplements to enhance growth performance, immune function, and disease resistance in L. vannamei aquaculture, offering a promising strategy for sustainable shrimp farming.

Ichthyobodo necator is a damaging and economically important protozoan parasite; however, its clinical patterns and incidence, correlated to environmental factors, are still poorly understood. This study provides the first report of Ichthyobodo necator infestation among Dicentrarchus labrax. We recorded significant mortalities in the cultured D. labrax of average size (5.92 g weight, and 11.55 cm length) in El-Max Station, National Institute of Oceanography and Fisheries, NIOF, Egypt, during the period extending from early summer to early fall (June to October) 2023. Behavioral and gross lesions of the infested fish were recorded; besides, dead and moribund fish were collected. Wet smears of the skin and gill of the affected fish were examined by compound light microscopy. Moreover, water samples from the affected ponds were collected and examined for their physicochemical parameters. The bodonid biflagellated Ichthyobodo necator (Henneguy) C. Pinto, 1928 was isolated from the skin and gills and identified based on specific morphological characteristics. DNA sequencing of PCR products and phylogenetic analysis confirmed identification, with clustering of the current isolates with I. necator isolates from different fish species. The multivariate analysis revealed a positive correlation between the prevalence and infestation intensity of Ichthyobodo, increased temperature levels, decreased dissolved oxygen DO, and also correlated with higher ammonia, and pH values. Additionally, the elevated concentrations of iron, calcium, magnesium, zinc, and copper in pond water were positively correlated with infestation and mortalities. These water parameter levels promote respiratory distress, accelerated prevalence, and infestation intensities of I. necator, particularly during the infestation peak in August and September. This study bridges the knowledge gap regarding I. necator parasite infestations and their correlation with water quality parameters.

Phytobiotics are promising diet alternatives, yet their effectiveness in high-risk aquaculture conditions remains underexplored. Therefore, a 90-day feeding trial was conducted based on dietary supplementation of Nile tilapia, Oreochromis niloticus, with herbal extracts, namely, lemon balm [Melissa officinalis (MOE)], marjoram [Origanum majorana (OME)], and chamomile [Matricaria chamomilla (MCE)] with 0% water change. The treated groups were compared to groups untreated with herbs or control groups [positive control (PC; 0% water change) and negative control (NC; 20% water exchange per day]. Fish were cultured at stocking density (20 fish m^-3: 1.8kg of biomass/m3). We conducted a physicochemical analysis of the water and the clinical responses, growth, and immune responses of the fish were evaluated. Furthermore, the herbal-supplemented fish were then challenged with a pathogenic Edwardseilla tarda strain and mortality was monitored. In the 1^st and 2^nd months, the water parameters were within the permissible limits. After that, a fatally low dissolved oxygen concentration and the highest levels of ammonia, nitrite, nitrate, and pH were recorded during the 3^rd month. Blood and immune assays were conducted in the treated groups and control groups. The herbal-treated groups appeared healthy, but during the 3rd month, lethargy and decreased appetite were evident. Generally, the herbal-treated fish showed improved growth performance parameters, survival rates, and resistance against pathogenic bacteria E. tarda, particularly in the OME and MOE-treated groups compared to the positive control group. Finally, phytobiotic supplements were shown to improve fish stress tolerance and immune activation for a certain period under stressful conditions or unchanged water, based on the stocking density, dosages of herbs used, and the extent of deterioration of the water quality.

Isopodiosis in cultured meagre Argyrosomus regius was investigated at 3 farms in the northern lakes of Egypt throughout 2018, based upon prevalence rate, parasitological examination, and molecular identification by PCR targeting the large ribosomal subunit 16S of the rRNA gene. Further, the susceptibility of A. regius to isopod infection was experimentally evaluated under hyposalination of 25, 15, and 8 ppt for 1 wk. The isolated isopod stages were morphologically identified as Livoneca redmanii Leach, 1818 with prevalence rates of 77.05 and 77.9% in Al-Madiyyah and Sidi Krir, respectively. The highest prevalence and salinity of 78.85% and 30-34 ppt were reported in El Matareya. DNA sequencing and molecular analysis confirmed the identification of L. redmanii. A. regius experimentally infected with L. redmanii under a hyposalination protocol at 15 and 8 ppt showed marked reduction in mortality (20 and 50%, respectively), and infection prevalence (40 and 63.33%, respectively). The serum lysozyme concentration and nitric oxide of treated fish at 15 and 8 ppt were significantly increased compared to those held at 25 and 33 ppt, whereas serum osmolality levels were higher at 25 and 33 ppt. To our knowledge, this is the first molecular characterization of L. redmanii in cultured A. regius in Egypt.

The current work aimed to study the types and seasonal occurrence of digenetic trematodes in D. labrax cultured in Egypt. A total number of 1800 D. labrax, (150/season- 600/farm) of average weight 95.14±10.37 gm were collected from three Egyptian farms during 2019. Four digeneans were isolated from the gastrointestinal tract; Metadena crassulata Derogenes varicus, Acanthostomum spiniceps, and Diplomonorchis sphaerovarium. The highest infection rate was detected in Farm 2 (30.16 %), specifically at spring (27.76% ), where the range of water temperature was 21.12- 24.63 oC, and salinity 15.85-32.34 ppt. The infected fish were apparently healthy, except in heavy infestation where body weakness and anemia of the internal organs were evident. The infected fingerling recoded the lowest condition factor (0.98) and mean parasitic intensity of 3.9, but higher values were noticed in juvenile, adult, and broodstock. Moreover, weak linear regression was reported between infection intensity and weight (R=0.91), fish length (R=0.964), and condition factor (0.956). Remarkable pathological alterations were observed in the intestine of infected fish, including edema, aggregation of inflammatory cells, mucinous degeneration and sloughed necrotic areas. Therefore, preventive and control measures are recommended to avoid such infections that potentially influence the health status and productivity of infected fishes