Chlorella vulgaris algae ameliorates chlorpyrifos toxicity in Nile tilapia with special reference to antioxidant enzymes and Streptococcus agalactiae infection.

BACKGROUND: Chlorpyrifos (CPF) is a widely used pesticide in the production of plant crops. Despite rapid CPF biodegradation, fish were exposed to wastewater containing detectable residues. Recently, medicinal plants and algae were intensively used in aquaculture to replace antibiotics and ameliorate stress impacts. METHODS AND RESULTS: An indoor experiment was conducted to evaluate the deleterious impacts of CPF pollution on Nile tilapia health and the potential mitigation role of Chlorella vulgaris algae. Firstly, the median lethal concentration LC50 - 72 h of CPF was determined to be 85.8 µg /L in Nile tilapia (35.6 ± 0.5 g body weight) at a water temperature of 27.5 °C. Secondly, fish were exposed to 10% of LC50 - 72 h for six weeks, and tissue samples were collected and examined every two weeks. Also, Nile tilapia were experimentally infected with Streptococcus agalactiae. Exposed fish were immunosuppressed expressed with a decrease in gene expressions of interleukin (IL) 1ß, IL-10, and tumor necrosis factor (TNF)-α. Also, a decline was recorded in glutathione peroxidase (GPx), superoxide dismutase (SOD), and catalase (CAT) gene expression in the head kidney tissue. A high mortality rate (MR) of 100% was recorded in fish exposed to CPF for six weeks and challenged with S. agalactiae. Fish that received dietary C. vulgaris could restore gene expression cytokines and antioxidants compared to the control. After six weeks of CPF exposure, fish suffered from anemia as red blood cell count (RBCs), hemoglobin (Hb), and packed cell volume (PCV) significantly declined along with downregulation of serum total protein (TP), globulin (GLO), and albumin (ALB). Liver enzymes were significantly upregulated in fish exposed to CPF pollution, alanine aminotransferase (ALT) (42.5, 53.3, and 61.7 IU/L) and aspartate aminotransferase (AST) (30.1, 31.2, and 22.8) after 2, 4, and 6 weeks, respectively. On S. agalactiae challenge, high MR was recorded in Nile tilapia exposed to CPF (G3) 60%, 60%, and 100% in week 2, week 4, and week 6, and C. vulgaris provided a relative protection level (RPL) of 0, 14.29, and 20%, respectively. CONCLUSIONS: It was concluded that CPF pollution induces immunosuppressed status, oxidative stress, and anemic signs in Nile tilapia. In contrast, C. vulgaris at a 50 g/kg fish feed dose could partially ameliorate such withdrawals, restoring normal physiological parameters.

Influence of taurine on the zootechnical performance and health parameters of juvenile Nile tilapia in a recirculating aquaculture system.

Taurine is considered a conditionally essential amino acid for fish, so its supplementation may improve feed conversion. This study evaluated the supplementation of taurine on growth performance, hematological and immunological parameters, production costs, and survival of Nile tilapia (Oreochromis niloticus) juveniles raised in a recirculating aquaculture system (RAS). A control diet was formulated with 360 g kg-1 of crude protein without fish meal and without taurine supplementation (Control). From the control diet, another diet supplemented with 9.7 g of taurine per kg of feed (Taurine) was produced. Fish fed diet supplemented with taurine had lower daily average weight gain and final average weight compared to the control diet (p < 0.05). It was observed that taurine had no influence on condition factor, survival, or hemato-immunological parameters of Nile tilapia juveniles, but there was a higher mean corpuscular volume and greater nitrogen retention in fish from the control group (p < 0.05). It is concluded that Nile tilapia juveniles do not benefit from taurine supplementation in RAS, even when fed diet containing plant-based protein sources.

Heavy metal levels and human health risk implications associated with fish consumption from the lower Omo river (Lotic) and Omo delta lake (Lentic), Ethiopia.

This study is the first to determine the levels of heavy metals in commercially important fish species, namely Lates niloticus and Oreochromis niloticus and the potential human health risks associated with their consumption. A total of 120 fish samples were collected from the lower Omo river and Omo delta, with 60 samples from each water source. The fish tissue samples (liver and muscle) were analyzed using a flame atomic absorption spectrometer for nine heavy metals (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn). The human health risk assessment tools used were the target hazard quotient (THQ), the hazard index (HI), and the target cancer risk (TCR). The mean levels of heavy metals detected in the liver and muscle of L. niloticus from the lower Omo river generally occurred in the order Fe > Zn > Pb> Cu > Mn> Cr > Co > Ni and Pb > Cu > Mn > Co > Ni, respectively. The mean levels of metals in the muscle and liver tissues of O. niloticus were in the order Fe > Pb > Zn > Mn > Cu > Cr > Co > Ni and Pb > Zn > Mn > Fe > Cu > Co > Ni, respectively. Similarly, the mean levels of heavy metals detected in the liver and muscle of L. niloticus from Omo delta occurred in the order Fe > Zn > Pb > Cu > Mn > Cr > Co > Ni and Fe > Pb > Zn > Mn > Cu > Co > Cr > Ni, respectively. The mean levels in the muscle and liver tissues of O. niloticus from the Omo delta were in the order Fe > Pb > Zn > Mn > Cu > Cr > Co > Ni and Pb > Fe > Zn > Mn > Co > Cu > Ni, respectively. The study revealed that the THQ values were below 1, indicating that consumption of L. niloticus and O. niloticus from the studied sites does not pose a potential non-carcinogenic health risk. Although the TCR values for Pb in this study were within the tolerable range, it's mean concentration in the muscle and liver tissues of both fish species from the two water bodies exceeded the permissible limit established by FAO/WHO. This is a warning sign for early intervention, and it emphasizes the need for regular monitoring of freshwater fish. Therefore, it is imperative to investigate the pollution levels and human health risks of heavy metals in fish tissues from lower Omo river and Omo delta for environmental and public health concerns.

Relatedness of hypoxia and hyperthermia tolerances in the Nile tilapia (Oreochromis niloticus) and their relationships with cardiac and gill traits.

In fish, thermal and hypoxia tolerances may be functionally related, as suggested by the oxygen- and capacity-limited thermal tolerance (OCLTT) concept, which explains performance failure at high temperatures due to limitations in oxygen delivery. In this study the interrelatedness of hyperthermia and hypoxia tolerances in the Nile tilapia (Oreochromis niloticus), and their links to cardiorespiratory traits were examined. Different groups of O. niloticus (n = 51) were subjected to hypoxia and hyperthermia challenges and the O2 tension for aquatic surface respiration (ASR pO2) and critical thermal maximum (CTmax) were assessed as measurement endpoints. Gill filament length, total filament number, ventricle mass, length and width were also measured. Tolerance to hypoxia, as evidenced by ASR pO2 thresholds of the individual fish, was highly variable and varied between 0.26 and 3.39 kPa. ASR events increased more profoundly as O2 tensions decreased below 2 kPa. The CTmax values recorded for the O. niloticus individuals ranged from 43.1 to 44.8 °C (Mean: 44.2 ± 0.4 °C). Remarkably, there was a highly significant correlation between ASR pO2 and CTmax in O. niloticus (r = -0.76, p < 0.0001) with ASR pO2 increasing linearly with decreasing CTmax. There were, however, no discernible relationships between the measured cardiorespiratory properties and hypoxia or hyperthermia tolerances. The strong relationship between hypoxia and hyperthermia tolerances in this study may be related to the ability of the cardiorespiratory system to provide oxygen to respiring tissues under thermal stress, and thus provides some support for the OCLTT concept in this species, at least at the level of the entire organism.

Immunological and molecular evaluation of zoonotic metacercarial infection in freshwater fish: A cross-sectional analysis.

Improperly cooked fish, carrying active metacercariae (MCs), can pose a significant risk for transmitting fish-borne zoonotic trematodes (FBZTs) to human consumers. This study aimed to enhance our understanding of FBZTs by conducting a comprehensive cross-sectional analysis involving various fish species, such as Nile tilapia (Oreochromis niloticus), African catfish (Clarias gariepinus), and red-belly tilapia (Tilapia zillii). These fish specimens were collected from distinct Egyptian governorates, specifically Giza, Kafr al-Shaykh, and Fayoum. The recovered flukes from experimentally infected domestic pigeons were identified as Prohemistomum vivax, Haplorchis pumilio, and Pygidiopsis genata based on morphological features. Furthermore, the identity of the retrieved adult flukes was confirmed using three species-specific primers for PCR amplification and sequencing analysis of the ITS rDNA region and have been deposited in GenBank with the following accession numbers: P. vivax (OR291421.1 and OR291422.1), P. genata (OP099561.1), and H. pumilio (OM439581.1-OP090510.1). Quantitative real-time PCR targeting the immunological genes Tumor Necrosis Factor-alpha (TNF-alpha) and Interleukin-1 (IL-1Β) was employed to compare the cellular immune response between infected with EMCs and uninfected O. niloticus. The results indicated a significant increase in TNF- and IL-1Β levels in FBZTs-infected vs un-infected fishes. Importantly, the presence of adult flukes and EMCs led to substantial histological alterations in both experimentally infected pigeons and naturally infected fish tissues. These changes included the necrosis of fish muscle bundles and a pronounced inflammatory reaction with muscular necrosis in the digestive tracts of experimentally infected pigeons.

Impact of Sel-Plex® dietary supplementation on growth performance, physiological response, oxidative status, and immunity-linked gene expression in Nile tilapia (Oreochromis niloticus) fingerlings challenged with Aeromonas hydrophila.

Background: Organic selenium (Sel-Plex®) supplementation holds considerable promise for improving the effectiveness of fish production. Aim: This experiment was accomplished to judge the potential benefits of Sel-Plex® nutritional additive on growth outcomes, physiological response, oxidative status, and immunity-linked gene expression in Nile tilapia (Oreochromis niloticus) fingerlings exposed to bacterial infection with Aeromonas hydrophila. Methods: Utilizing a basal diet of 30% protein, four experimental diets were prepared, each of which contained Sel-Plex® at concentrations of 0.0, 0.5, 1, and 2 mg/kg, respectively. Three replicates of 20 fish/treatment were used using 240 healthy Nile tilapia fingerlings. Fish were placed in 12 glass aquariums and separated into 4 groups at random. For the entire span of 8 weeks, diets were admitted to fish at a 3% rate of fish biomass/aquarium. After the feeding trial, pathogenic A. hydrophila was intraperitoneally injected into fish of each treatment, and fish were observed for 15 days to track the survival rate (SR) after the challenge. Results: Growth performance, physiological response, immunological parameters (phagocytic activity, phagocytic index, and lysozyme), and antioxidant parameters [catalase, superoxide dismutase (SOD), malondialdehyde, and glutathione peroxidase (GPx)] were noticeably improved in Sel-Plex® treated groups. Moreover, Sel-Plex® increased gene expression linked with the immune system in the liver (tumor necrosis factor-alpha and interleukin 1ß), to growth (insulin-like growth factor 1 and growth hormone receptor), and antioxidants (SOD and GPx). Under pathogen-challenge conditions, the employed dietary Sel-Plex® supplementation could successfully lower fish oxidative stress, offering a potential preventive additive for Nile tilapia instead of antibiotics. On the other hand, Sel-Plex® significantly enhanced each of three intestinal morphological measurements (villus width, villus length, and crypt depth), demonstrating the greatest influence on the improvement of intestinal structure overall. In the Nile tilapia control group, the infection with A. hydrophila caused noticeable degenerative alterations in the gut, hepatopancreas, spleen, and posterior kidney. The severity of the lesion was significantly reduced and significantly improved with higher Sel-Plex® concentrations. Sel-Plex® supplemented groups had 100% SRs among the A. hydrophila-challenged groups. Conclusion: It could be advised to enrich the diets of Nile tilapia fingerlings with 1-2 mg.kg-1 of Sel-Plex® to enhance growth rate, physiological response, immunological reaction, and intestinal absorptive capacity.

Ameliorative effect of BIO-MOS® as a dietary supplementation on growth performance, physiological response, oxidative status, and immunity-linked gene expression in Nile tilapia (Oreochromis niloticus) fingerlings challenged with Aeromonas hydrophila.

Background: Mannanoligosaccharides (MOS) usage in fish production has drawn more attention because of their positive benefits on disease resistance and fish performance. Aim: The ongoing research was executed to assess the potential advantages of Bio-Mos® dietary supplementation regarding the growth outcomes, physiological response, oxidative biomarkers, and immunity-linked gene expression in Nile tilapia (Oreochromis niloticus) fingerlings exposed to bacterial infection with Aeromonas hydrophila. Methods: Four experimental diets were developed using a 30% protein baseline diet, with Bio-Mos® added at variable levels; 0.0, 0.5, 1, and 2 g/kg, respectively. 240 healthy Nile tilapia fingerlings were split into 4 groups at random and assigned to 12 glass aquariums (three replicates of 20 fish/treatment). Diets were admitted at a 3% rate of fish biomass/aquarium for 8 weeks. Following the feeding trial, fish from every treatment were intraperitoneally injected with pathogenic A. hydrophila, and then observed for 15 days to record the survival rate percent (SR%) post challenge. Results: Results revealed significant improvement in growth performance, physiological response, immunological parameters (phagocytic index, phagocytic activity, and lysozyme), and antioxidant parameters [catalase, malondialdehyde, glutathione peroxidase (GSH-Px), and superoxide dismutase (SOD)] among Bio-Mos® treated groups. Moreover, Bio-Mos® increased the expression of tumor necrosis factor alpha and Interleukin 1ß, genes linked to the liver immune system. Growth-related genes (GHr), antioxidant-related genes (SOD and GSH-Px). In fish subjected to pathogens, dietary MOS supplementation could significantly lower oxidative stress, showing promise as a preventative supplement for Nile tilapia in place of antibiotics. On the other hand, Bio-Mos® considerably improved each of the three intestinal morphological measures (villus width, villus length, and crypt depth), showing the best overall intestinal structure-improving impact. The challenge with A. hydrophila caused marked degenerative alterations in the intestine, hepatopancreas, spleen, and posterior kidney of Nile tilapia, in the control group. However, lesion severity was greatly decreased and showed marked amelioration with an increased concentration of Bio-Mos®. The A. hydrophila-challenged groups revealed a 100% SR% mainly among the Bio-Mos® supplemented groups. Conclusion: It is recommended to enrich the Nile tilapia fingerlings diets with 2 g.kg-1 of MOS for better results on the growth rate, physiological response, immunological response, and intestinal absorptive capacity.

The impact of dietary probiotic supplementation on welfare and growth performance of Nile tilapia (Oreochromis niloticus).

Background: The usage of commercial probiotic products as alternatives to traditional antibiotics in fish culture is initiated to be a potential factor for Nile tilapia fish's welfare and growth. Aim: The purpose of the current study is to show the influence of commercial probiotics (Bacillus amyloliquefaciens) dietary supplementation at different levels on Nile tilapia welfare and growth. Methods: Apparently healthy fingerlings of Nile Tilapia with a total number of 120 with an average initial weight (26.2 ± 0.3 g) were distributed into four groups (each group had 30 fingerlings). The first group (G1) was given a basal diet without additional probiotics, while other groups [second group (G2), the third group (G3), and the fourth group (G4)] were given basal diets supplemented with different levels of commercial probiotics (1 g, 2 g, and 3 g of probiotics per kilogram of diet), respectively (15 fish in each sub group as replicate), in eight glass aquaria (30 × 40 × 100 cm) for 2 months as an experimental period. Results: The results revealed that the probiotic-treated groups especially G4 (3 g probiotics/kg diet) showed a marked increase in the following behavioral patterns such as feeding and swimming behaviors, while G2 (1 g probiotic/kg diet) had an increase in the foraging behavior compared with G1 control group. While surfacing, body care, and aggressive behaviors with all patterns were the highest in the control group (G1) than all probiotics-treated groups. The crossing test showed that fish rose in the probiotic-treated groups (G3 and G4) were more active and could achieve the highest growth rates. While water quality was better in G4 (3 g probiotic /kg diet) than in other groups. Moreover, G4 (3 g probiotic/kg diet) showed a marked increase in all serum biochemical parameters than the control group (G1). Conclusion: The current study proved that the best level of commercial probiotics (B. amyloliquefaciens) was (3 g probiotic/kg diet) for achieving optimal Nile tilapia fingerlings' growth performance under these experimental conditions. Finally, this work confirms the significance of the addition of probiotics as a feed additive to enhance both growth performance and immunity response, improve water quality, and achieve the welfare of Nile tilapia fingerlings.

Summer mortality syndrome bacterial pathogens in farmed Nile tilapia (Oreochromis niloticus).

Background: The high summer mortality in many fish farms, which had detrimental economic and social implications, was a serious challenge that the fish industry had to deal with. Aim: With an examination of the most effective antibiotic, the ongoing research was intended to shed light on the identification of the main bacterial pathogens associated with the summer mortality syndrome in the diseased farmed Nile tilapia. Methods: Six hundred dead Nile tilapia samples that had suffered from summer mortality were collected from several fish farms between May and October of 2022. The gathered fish displayed hemorrhagic areas on the skin, scale detachment, fin degeneration, erosions, skin ulcers, and corneal opacity with unilateral and/or bilateral exophthalmia. The most prominent internal appearance was swelling of the internal organs with sanguineous ascetic fluid. Results: There were 225 bacterial isolates found. Six species were identified through phenotypic and biochemical analysis; they were Aeromonas, Vibrio, Streptococcus, Pseudomonas, Enterococcus, and Edwardsiella spp., in descending percentage, respectively. Aeromonas spp., Vibrio spp., and Streptococcus spp. were the three most frequent isolated bacterial pathogens. The identification of Aeromonas hydrophila, Vibrio spp., and Streptococcus iniae, the three most common bacterial isolates, was confirmed by molecular analysis by polymerase chain reaction. Most of the tested strains were found to be responsive to Ciprofloxacin (CIP), Gentamicin (CN), and Chloramphenicol (C) but resistant to Amoxicillin (AMX), according to an antibiotic sensitivity test. Conclusion: The three most dangerous common bacterial infections discovered during mass-farmed tilapia summer mortality are A. hydrophil a, Vibrio sp., and S. iniae. This makes it clear that high water temperatures may raise the possibility of bacterial infections, which could cause widespread tilapia mortality and substantial financial losses. Therefore, it is crucial to maintain a beneficial fish culture, environment, and husbandry practices to enhance the tilapia-rearing environment and lessen the virulence of the disease. Isolated bacterial strains showed low levels of resistance to AMX but were vulnerable to CIP, CN, and C.

Effects of Shrimp Shell-Derived Chitosan on Growth, Immunity, Intestinal Morphology, and Gene Expression of Nile Tilapia (Oreochromis niloticus) Reared in a Biofloc System.

Chitosan (CH) shows great potential as an immunostimulatory feed additive in aquaculture. This study evaluates the effects of varying dietary CH levels on the growth, immunity, intestinal morphology, and antioxidant status of Nile tilapia (Oreochromis niloticus) reared in a biofloc system. Tilapia fingerlings (mean weight 13.54 ± 0.05 g) were fed diets supplemented with 0 (CH0), 5 (CH5), 10 (CH10), 20 (CH20), and 40 (CH40) mL·kg-1 of CH for 8 weeks. Parameters were assessed after 4 and 8 weeks. Their final weight was not affected by CH supplementation, but CH at 10 mL·kg-1 significantly improved weight gain (WG) and specific growth rate (SGR) compared to the control (p < 0.05) at 8 weeks. Skin mucus lysozyme and peroxidase activities were lower in the chitosan-treated groups at weeks 4 and 8. Intestinal villi length and width were enhanced by 10 and 20 mL·kg-1 CH compared to the control. However, 40 mL·kg-1 CH caused detrimental impacts on the villi and muscular layer. CH supplementation, especially 5-10 mL·kg-1, increased liver and intestinal expressions of interleukin 1 (IL-1), interleukin 8 (IL-8), LPS-binding protein (LBP), glutathione reductase (GSR), glutathione peroxidase (GPX), and glutathione S-transferase (GST-α) compared to the control group. Overall, dietary CH at 10 mL·kg-1 can effectively promote growth, intestinal morphology, innate immunity, and antioxidant capacity in Nile tilapia fingerlings reared in biofloc systems.

Foraging-induced craniofacial plasticity is associated with an early, robust and dynamic transcriptional response.

Phenotypic plasticity is the ability of a single genotype to vary its phenotype in response to the environment. Plasticity of the skeletal system in response to mechanical input is widely studied, but the timing of its transcriptional regulation is not well understood. Here, we used the cichlid feeding apparatus to examine the transcriptional dynamics of skeletal plasticity over time. Using three closely related species that vary in their ability to remodel bone and a panel of 11 genes, including well-studied skeletal differentiation markers and newly characterized environmentally sensitive genes, we examined plasticity at one, two, four and eight weeks following the onset of alternate foraging challenges. We found that the plastic species exhibited environment-specific bursts in gene expression beginning at one week, followed by a sharp decline in levels, while the species with more limited plasticity exhibited consistently low levels of gene expression. This trend held across nearly all genes, suggesting that it is a hallmark of the larger plasticity regulatory network. We conclude that plasticity of the cichlid feeding apparatus is not the result of slowly accumulating gene expression difference over time, but rather is stimulated by early bursts of environment-specific gene expression followed by a return to homeostatic levels.

Polystyrene nanoplastic and engine oil synergistically intensify toxicity in Nile tilapia, Oreochromis niloticus : Polystyrene nanoplastic and engine oil toxicity in Nile tilapia.

Polystyrene nanoplastic (PS-NPs) and Engine oil (EO) pose multiple ecotoxic effects with increasing threat to fish ecosystems. The current study investigated the toxicity of 15 days exposure to PS-NPs and / or EO to explore their combined synergistic effects on Nile tilapia, Oreochromis niloticus (O. niloticus). Hematobiochemical parameters, proinflammatory cytokines, and oxidative stress biomarkers as well as histological alterations were evaluated. The experimental design contained 120 acclimated Nile tilapia distributed into four groups, control, PS-NPs (5 mg/L), EO (1%) and their combination (PS-NPs + EO). After 15-days of exposure, blood and tissue samples were collected from all fish experimental groups. Results indicated that Nile tilapia exposed to PS-NPs and / or EO revealed a significant decrease in almost all the measured hematological parameters in comparison to the control, whereas WBCs and lymphocyte counts were significantly increased in the combined group only. Results clarified that the combined PS-NPs + EO group showed the maximum decrease in RBCs, Hb, MCH and MCHC, and showed the maximum significant rise in interleukin-1ß (IL-1ß), and interleukin-6 (IL-6) in comparison to all other exposed groups. Meanwhile, total antioxidant capacity (TAC) showed a significant (p < 0.05) decline only in the combination group, whereas reduced glutathione (GSH) showed a significant decline in all exposed groups in comparison to the control. Both malondialdehyde (MDA) and aspartate aminotransferase (AST) showed a significant elevation only in the combination group. Uric acid showed the maximum elevation in the combination group than all other groups, whereas creatinine showed significant elevation in the EO and combination group when compared to the control. Furthermore, the present experiment proved that exposure to these toxicants either individually or in combination is accompanied by pronounced histomorpholgical damage characterized by severe necrosis and hemorrhage of the vital organs of Nile tilapia, additionally extensively inflammatory conditions with leucocytes infiltration. We concluded that combination exposure to both PS-NPs and EO caused severe anemia, extreme inflammatory response, oxidative stress, and lipid peroxidation effects, thus they can synergize with each other to intensify toxicity in fish.

Serotype distribution, virulence and antibiotic resistance of Streptococcus agalactiae isolated from cultured tilapia Oreochromis niloticus in Lake Volta, Ghana.

Streptococcus agalactiae infection is one of the major factors limiting the expansion of tilapia farming globally. In this study, we investigated the serotype distribution, virulence and antimicrobial resistance of S. agalactiae isolates from tilapia farmed in Lake Volta, Ghana. Isolates from 300 moribund fish were characterised by Gram staining, MALDI-TOF/MS and 16S rRNA sequencing. Serotype identification was based on multiplex polymerase chain reaction (PCR) amplification of the capsular polysaccharide genes. Detection of virulence genes (cfb, fbsA and cspA) and histopathology were used to infer the pathogenicity of the isolates. The susceptibility of isolates to antibiotics was tested using the Kirby-Bauer disk diffusion assay. All 32 isolates identified as S. agalactiae were of serotype Ia. This was notably different from isolates previously collected from the farms in 2017, which belonged to serotype Ib, suggesting a possible serotype replacement. The prevalence of the pathogen was related to the scale of farm operation, with large-scale farms showing higher S. agalactiae positivity. Data from histopathological analysis and PCR amplification of targeted virulence genes confirmed the virulence potential and ability of the isolates to cause systemic infection in tilapia. Except for gentamicin, the majority of the isolates were less resistant to the tested antibiotics. All isolates were fully sensitive to oxytetracycline, erythromycin, florfenicol, enrofloxacin, ampicillin and amoxicillin. This study has improved our understanding of the specific S. agalactiae serotypes circulating in Lake Volta and demonstrates the need for continuous monitoring to guide the use of antimicrobials and vaccines against streptococcal infections in Ghanaian aquaculture systems.

Parasites (Monogenea) of tilapias Oreochromis niloticus and Coptodon rendalli (Cichlidae) in a river spring in Brazil.

In the present study, we examined 30 individuals of introduced African cichlids, Oreochromis niloticus and Coptodon rendalli, collected in a river spring of the Pardo River, Paranapanema River basin, southeastern Brazil. Based on morphological and molecular analyses of the partial LSU rDNA gene, we identified four species of monogeneans, Cichlidogyrus tilapiae, C. thurstonae, C. mbirizei, and Scutogyrus longicornis on the gills of O. niloticus, whereas individuals of C. rendalli were infested only with C. papernastrema. This is the first record of C. mbirizei and C. papernastrema in tilapias from Brazil. The ecological consequences of the introduction of exotic species of tilapia such as O. niloticus and C. rendalli along with their monogenean parasites in a wild environment represented by a river spring are discussed. Our new molecular data on Cichlidogyrus and Scutogyrus contribute to the investigation of the phylogenetic interrelationships of these widely distributed genera of monogeneans since their species composition is still unsettled.

Title: Parasites (Monogenea) des tilapias Oreochromis niloticus et Coptodon rendalli (Cichlidae) dans une source au Brésil. Abstract: Dans la présente étude, nous avons examiné 30 individus de cichlidés africains introduits, Oreochromis niloticus et Coptodon rendalli, collectés dans une source fluviale du fleuve Pardo, bassin du fleuve Paranapanema, dans le sud-est du Brésil. Sur la base d'analyses morphologiques et moléculaires du gène partiel de l'ADNr LSU, nous avons identifié quatre espèces de monogènes, Cichlidogyrus tilapiae, C. thurstonae, C. mbirizei et Scutogyrus longicornis sur les branchies d'O. niloticus, alors que les individus de C. rendalli étaient infestés uniquement par C. papernastrema. Il s'agit du premier signalement de C. mbirizei et C. papernastrema chez des tilapias du Brésil. Les conséquences écologiques de l'introduction d'espèces exotiques de tilapia telles que O. niloticus et C. rendalli ainsi que leurs monogènes parasites dans un environnement sauvage représenté par une source fluviale sont discutées. Nos nouvelles données moléculaires sur Cichlidogyrus et Scutogyrus contribuent à l'étude des interrelations phylogénétiques de ces genres de monogènes largement distribués puisque leur composition spécifique est encore incertaine.

Repeated Divergence in Opsin Gene Expression Mirrors Photic Habitat Changes in Rapidly Evolving Crater Lake Cichlid Fishes.

AbstractSelection pressures differ along environmental gradients, and traits tightly linked to fitness (e.g., the visual system) are expected to track such variation. Along gradients, adaptation to local conditions might be due to heritable and nonheritable environmentally induced variation. Disentangling these sources of phenotypic variation requires studying closely related populations in nature and in the laboratory. The Nicaraguan lakes represent an environmental gradient in photic conditions from clear crater lakes to very turbid great lakes. From two old, turbid great lakes, Midas cichlid fish (Amphilophus cf. citrinellus) independently colonized seven isolated crater lakes of varying light conditions, resulting in a small adaptive radiation. We estimated variation in visual sensitivities along this photic gradient by measuring cone opsin gene expression among lake populations. Visual sensitivities observed in all seven derived crater lake populations shifted predictably in direction and magnitude, repeatedly mirroring changes in photic conditions. Comparing wild-caught and laboratory-reared fish revealed that 48% of this phenotypic variation is genetically determined and evolved rapidly. Decreasing intrapopulation variation as environments become spectrally narrower suggests that different selective landscapes operate along the gradient. We conclude that the power to predict phenotypic evolution along gradients depends on both the magnitude of environmental change and the selective landscape shape.

Distribution of bacteria and antimicrobial resistance in retail Nile tilapia (Oreochromis spp.) as potential sources of foodborne illness.

This study aimed to investigate AMR profiles of Aeromonas hydrophila, Salmonella spp., and Vibrio cholerae isolated from Nile tilapia (Oreochromis spp.) (n = 276) purchased from fresh markets and supermarkets in Bangkok, Thailand. A sample of tilapia was divided into three parts: fish intestine (n = 276), fish meat (n = 276), and liver and kidney (n = 276). The occurrence of A. hydrophila, Salmonella, and V. cholerae was 3.1%, 7.4%, and 8.5%, respectively. A high prevalence of these pathogenic bacteria was observed in fresh market tilapia compared to those from supermarkets (p < 0.05). The predominant Salmonella serovars were Paratyphi B (6.4%), followed by Escanaba (5.7%), and Saintpaul (5.7%). All isolates tested positive for the virulence genes of A. hydrophila (aero and hly), Salmonella (invA), and V. cholerae (hlyA). A. hydrophila (65.4%), Salmonella (31.2%), and V. cholerae (2.9%) showed multidrug resistant isolates. All A. hydrophila isolates (n = 26) exhibited resistant to ampicillin (100.0%) and florfenicol (100.0%), and often carried sul1 (53.8%) and tetA (50.0%). Salmonella isolates were primarily resistant to ampicillin (36.9%), with a high incidence of blaTEM (26.2%) and qnrS (25.5%). For V. cholerae isolates, resistance was observed against ampicillin (48.6%), and they commonly carried qnrS (24.3%) and tetA (22.9%). To identify mutations in the quinolone resistance determining regions (QRDRs), a single C248A point mutation of C248A (Ser-83-Tyr) in the gyrA region was identified in six out of seven isolates of Salmonella isolates. This study highlighted the presence of antimicrobial-resistant pathogenic bacteria in Nile tilapia at a selling point. It is important to rigorously implement strategies for AMR control and prevention.

Pseudomonas putida infection induces immune-antioxidant, hepato-renal, ethological, and histopathological/immunohistochemical disruptions in Oreochromis niloticus: the palliative role of titanium dioxide nanogel.

BACKGROUND: Pseudomonas putida is a pathogenic bacterium that induces great losses in fishes, including Nile tilapia (Oreochromis niloticus). Currently, the application of nanomaterials in aquaculture practices has gained more success as it endows promising results in therapies compared to traditional protocols. OBJECTIVE: Therefore, the current perspective is considered the first report to assess the anti-bacterial efficacy of titanium dioxide nanogel (TDNG) against Pseudomonas putida (P. putida) in Nile tilapia. METHODS: The fish (n = 200; average body weight: 47.50±1.32 g) were allocated into four random groups (control, TDNG, P. putida, and TDNG + P. putida), where 0.9 mg/L of TDNG was applied as bath treatment for ten days. RESULTS: Outcomes revealed that P. putida infection caused ethological alterations (surfacing, abnormal movement, and aggression) and depression of immune-antioxidant variables (complement 3, lysozyme activity, total antioxidant capacity, superoxide dismutase, and reduced glutathione content). Additionally, a substantial elevation in hepatorenal biomarkers (aspartate and alanine aminotransferases and creatinine) with clear histopathological changes and immuno-histochemical alterations (very weak BCL-2 and potent caspase-3 immuno-expressions) were seen. Surprisingly, treating P. putida-infected fish with TDNG improved these variables and obvious restoration of the tissue architectures. CONCLUSION: Overall, this report encompasses the key role of TDNG as an anti-bacterial agent for controlling P. putida infection and improving the health status of Nile tilapia.

Executive functions and brain morphology of male and female dominant and subordinate cichlid fish.

BACKGROUND: Living in a social dominance hierarchy presents different benefits and challenges for dominant and subordinate males and females, which might in turn affect their cognitive needs. Despite the extensive research on social dominance in group-living species, there is still a knowledge gap regarding how social status impacts brain morphology and cognitive abilities. METHODS: Here, we tested male and female dominants and subordinates of Neolamprologus pulcher, a social cichlid fish species with size-based hierarchy. We ran three executive cognitive function tests for cognitive flexibility (reversal learning test), self-control (detour test), and working memory (object permanence test), followed by brain and brain region size measurements. RESULTS: Performance was not influenced by social status or sex. However, dominants exhibited a brain-body slope that was relatively steeper than that of subordinates. Furthermore, individual performance in reversal learning and detour tests correlated with brain morphology, with some trade-offs among major brain regions like telencephalon, cerebellum, and optic tectum. CONCLUSION: As individuals' brain growth strategies varied depending on social status without affecting executive functions, the different associated challenges might yield a potential effect on social cognition instead. Overall, the findings highlight the importance of studying the individual and not just species to understand better how the individual's ecology might shape its brain and cognition.

Effects of Fat and Carnitine on the Expression of Carnitine Acetyltransferase and Enoyl-CoA Hydratase Short-Chain 1 in the Liver of Juvenile GIFT (Oreochromis niloticus).

Carnitine acetyltransferase (CAT) and Enoyl-CoA hydratase short-chain 1 (ECHS1) are considered key enzymes that regulate the ß-oxidation of fatty acids. However, very few studies have investigated their full length and expression in genetically improved farmed tilapia (GIFT, Oreochromis niloticus), an important aquaculture species in China. Here, we cloned CAT and ECHS1 full-length cDNA via the rapid amplification of cDNA ends, and the expressions of CAT and ECHS1 in the liver of juvenile GIFT were detected in different fat and carnitine diets, as were the changes in the lipometabolic enzymes and serum biochemical indexes of juvenile GIFT in diets with different fat and carnitine levels. CAT cDNA possesses an open reading frame (ORF) of 2167 bp and encodes 461 amino acids, and the ECHS1 cDNA sequence is 1354 bp in full length, the ORF of which encodes a peptide of 391 amino acids. We found that juvenile GIFT had higher lipometabolic enzyme activity and lower blood CHOL, TG, HDL-C, and LDL-C contents when the dietary fat level was 2% or 6% and when the carnitine level was 500 mg/kg. We also found that the expression of ECHS1 and CAT genes in the liver of juvenile GIFT can be promoted by a 500 mg/kg carnitine level and 6% fat level feeding. These results suggested that CAT and ECHS1 may participate in regulating lipid metabolism, and when 2% or 6% fat and 500 mg/kg carnitine are added to the feed, it is the most beneficial to the liver and lipid metabolism of juvenile GIFT. Our results may provide a theoretical basis for GIFT feeding and treating fatty liver disease.

Biocontrol of multidrug resistant pathogens isolated from fish farms using silver nanoparticles combined with hydrogen peroxide insight to its modulatory effect.

This study was divided into two parts. The first part involved the isolation, and detection of the prevalence and antimicrobial resistance profile of Aeromonas hydrophila, Pseudomonas aeruginosa, and Vibrio species from Nile tilapia fish and marine aquatic water. One hundred freshly dead Nile tilapia fish were collected from freshwater aquaculture fish farms located in Al-Abbassah district, Sharkia Governorate, and 100 samples of marine aquatic water were collected from fish farms in Port Said. The second part of the study focused on determining the in vitro inhibitory effect of dual-combination of AgNPs-H2O2 on bacterial growth and its down regulatory effect on crucial virulence factors using RT-PCR. The highest levels of A. hydrophila and P. aeruginosa were detected in 43%, and 34% of Nile tilapia fish samples, respectively. Meanwhile, the highest level of Vibrio species was found in 37% of marine water samples. Additionally, most of the isolated A. hydrophila, P. aeruginosa and Vibrio species exhibited a multi-drug resistance profile. The MIC and MBC results indicated a bactericidal effect of AgNPs-H2O2. Furthermore, a transcriptional modulation effect of AgNPs-H2O2 on the virulence-associated genes resulted in a significant down-regulation of aerA, exoU, and trh genes in A. hydrophila, P. aeruginosa, and Vibrio spp., respectively. The findings of this study suggest the effectiveness of AgNPs-H2O2 against drug resistant pathogens related to aquaculture.