Most tilapias are microphytes, but some prefer higher plants. Ammonia is one of the most important toxic compounds of nitrogen, which is a serious problem in the environment and aquaculture industry. In the present study, juvenile Oreochromis niloticus were exposed to 10, 20, and 30% (96h LC50) of ammonia for two weeks, which are equivalent to 0.9, 1.8, and 2.7 mg / l, respectively. After this period, the fish were anesthetized and blood samples were taken from the caudal stalk with a heparin syringe for evaluating blood indicators. The tissue samples were taken 0.5 cm from the liver, fixed in 10% formalin buffer, and after dehydration with alcohol, clarification with xylol, blocking with paraffin, and cutting 4-6 microns thick with microtome were done. Finally, the stained slides were studied with a light microscope. The results showed phenomena such as hyperemia, nuclear hypertrophy, sinusoidal dilatation, increased melanomacrophage centers, nucleus margination, hepatocyte vacuolation, and cell necrosis in the liver. In the studies of blood serum factors with the increase of ammonia, it has been increased in  AST, ALT, and ALP compared to the control and other groups. Also, as the ammonia concentration increased, the severity of the lesions also increased. Therefore, ammonia causes changes in the structure and activity of metabolic enzymes of the liver, which must be controlled by creating the appropriate ammonia and management conditions in the aquatic environment.

Several studies have reported the contamination of farmed fish by microcystins, however, alternations in levels of contamination resulting from seasonal changes are infrequently described. This investigation is focused on the seasonal accumulation of microcystins in farmed Nile Tilapia muscle tissue across three farms located in Zaria, Nigeria, as a means of assessing the health risks associated with the consumption of contaminated fish. Total microcystins and cyanobacteria content, respectively, in muscle tissue and gut of tilapia varied, seasonally in the farms. Microcystin levels were higher in fish tissues analyzed in the dry season than the rainy season at Nagoyi and Danlami ponds. Correlating with the levels of microcystins found in fish tissues, the highest dissolved microcystins levels in all the fish farms occurred in the dry season, where the Bal and Kol fish farm had the highest concentration (0.265 ± 0.038 μgL⁻¹). Gut analysis of fish obtained from the ponds, revealed a predominance of Microcystis spp. among other cyanobacteria. Estimation of total daily intake of consumed contaminated Nile tilapia muscles reveal values exceeding WHO recommended (0.04 μg kg⁻¹ body weight) total daily intake of MC-LR. Consumption of tilapia from Danlami pond presented the greatest risk with a value of 0.093 μg kg⁻¹ total daily intake. Results of the present study necessitate the implementation of legislation and monitoring programs for microcystins and other cyanobacteria contaminants of fish obtained from farms and other sources in Zaria and indeed several other African countries.

This paper is a part of a multi-disciplinary research “Application of Decentralized On-Site Water Treatment System in Egypt for Use in Agriculture and Producing Safe Fish and Animal Proteins”.The project aimed to investigate the environmental impact of implementing sewage water before and after treatment using the effluent of the on-site decentralized Japanese' Johkasou system, in agriculture and producing fish protein. The aim is to establish such system in Egypt to strengthen the sanitary conditions of water resources. In the present study, the impact of the sewage pollution in some fish farms at El-Fayyum, Port Said and El-Dakahlia governorates in Egypt was carried out. Water and fish (Oreochromis niloticus and Mugil cephalus) samples were collected from private fish farms of such localities. Bacteriological and chemical examination of water samples revealed the existence of coliforms and many other bacterial species of significant human health hazards. The chemical parameters of water showed a marked deviation from normal levels while examination of fish flesh specimens indicated contamination with Streptococcus Sp., Staphylococcus Sp., and Salmonella in all examined localities. Other bacterial isolates of human health importance (Morganella morganii, Pseudomonas cepacia and Enterococcos durans) were identified. The parasitological examination revealed the presence of encysted metacercariae (EMC); Diplostomatidae, Prohemistomatidae and Heterphyidae. Moreover, two protozoan parasites (Mxyoboulus tilapiae and Ichthyophthirius multifilis) were also recorded. The histopathological examination revealed mild tissue reaction in case of bacterial infection and severe pathological lesions in different organs in case of EMC infection. Lamellar hyperplasia and mononuclear cell infiltration in branchial tissue was common findings. In skeletal muscles, atrophy of muscle fibres, myolysis and myophagia were detected.

Aquaculture impacts on aquatic organic matter and ecosystem integrity are poorly understood, especially in tropical regions. Here, we investigated the impacts of Nile tilapia net cage farming on the elemental stoichiometry, fluorescence components, and stable isotopes of dissolved organic matter (DOM) of the large, tropical Furnas Reservoir (SE Brazil). Early-stage fish farming, i.e., relatively small and recently implemented farms, had detectable incipient effects on DOM characteristics, and these effects differed between reservoir branches. In the less eutrophic Rio Grande branch of the reservoir, we found a reduction in natural humic-like DOM components and an increase in a protein-like DOM component as far as 100 m away from fish farms. Further, we observed a decrease in δ¹⁵N-TDN due to fish farming. In the more eutrophic Rio Sapucaí branch, there were only local decreases in C:N ratios, as well as rises in C:P and N:P of DOM due to fish farming. These results suggest that early-stage fish farming had local but detectable effects on aquatic DOM that depended on previous eutrophication levels and highlight the need to assess the early impacts of fish farming on tropical reservoirs by combining different monitoring strategies.

Although the poultry production sector plays a key role in sustaining the majority of animal protein demand in Egypt, the deleterious effects of widespread antibiotic resistance on health and environment are currently not well recognized. Litter and dropping samples from broiler and layer poultry farms as well as, tilapia samples from the Nile River and aquaculture farms were collected from Upper Egypt. Samples were extracted and examined for tetracycline residues [tetracycline (TC), chlortetracycline (CTC), oxytetracycline (OTC) and doxycycline (DC)] using HPLC. In addition, tetracycline resistance genes [tet (M), tet (W), tet (Q) and tet (G)] were screened from pooled intestinal contents collected from twelve broiler farms in Upper Egypt. The antibiotic resistance genes results revealed that tet (W) was confirmed to be expressed in all intestinal samples. In contrast, tet (Q) and tet (M) were detected only in 42% and 17% of the samples, respectively. CTC and OTC were the antimicrobial compounds with the highest concentrations in poultry litter and droppings, with concentrations of 6.05 and 2.47 μg g−1 (CTC) and 5.9 and 1.33 μg g−1 (OTC), respectively. However, the concentrations of DC were significantly higher than those of the other compounds in both aquaculture and Nile River tilapia. The tetracycline residue levels in aquaculture tilapia were significantly higher than those in Nile River tilapia. The hazard quotients (HQs) exceeded 1 for OTC, CTC and DC, which highlights the great risk of using broiler litter to fertilize agricultural land. Moreover, the presence of DC and CTC indicates that consumption of aquaculture tilapia poses a considerable health risk. Therefore, poultry litter or droppings containing tetracycline residues and tet resistance determinants used for aquaculture or as farmland fertilizers could be major sources of antibiotic resistance in fish, humans and environment.

Environmental chemicals originating from human activities, such as persistent organic pollutants (POPs), may interfere with the endocrine system of aquatic organisms. The effect of these chemicals on biota and human populations is of high public concern but remains poorly understood, especially in aquatic environments of South America. The aim of this study was to investigate the bioavailability of POPs and the related effects in caged male tilapia (Oreochromis niloticus) in four cascading reservoirs of the Iguaçu River, Southern Brazil. POPs including organochlorine pesticides (OCPs), polychlorinated biphenyl (PCBs), and polybrominated diphenyl ethers (PBDEs) were determined in the reservoir water and tissue samples of tilapia after two months of exposure. The PCB levels in water (14.7 ng L−1) were 14 times higher than the limits permitted by the Brazilian legislation in the Salto Santiago (SS) reservoir. Similarly, concentrations of aldrin and its metabolites (6.05 ng L−1) detected in the water sample of the Salto Osório (SO) reservoir were also above the permitted limits. RT-qPCR analysis revealed different transcript levels of cytochrome P450 enzymes (CYP1A and CYP3A) in the liver among the four groups, with induced activity in tilapia from the SS reservoir. Quantification of the CYP3A mRNA expression and catalytic activity showed higher values for fish caged at the SS reservoir. The fish from this site also had a higher number of eosinophils observed in the testes. Although overt measurements of endocrine disruption were not observed in caged fish, alteration of CYP enzymes with co-occurrence of organochlorine contaminants in water may suggest bioavailability of contaminants from agricultural sources to biota. Additional studies with feral or caged animals for a longer duration may be necessary to evaluate the risks of the waterways to humans and wildlife.

Pyraclostrobin is a widely used and highly efficient fungicide that also has high toxicity to aquatic organisms, especially fish. Although some research has reported the toxic effects of pyraclostrobin on fish, the main toxic pathways of pyraclostrobin in fish remain unclear. The present study has integrated histopathological, biochemical and hematological techniques to reveal the main toxic pathways and mechanisms of pyraclostrobin under different exposure routes. Our results indicated that pyraclostrobin entered fish mainly through the gills. The highest accumulation of pyraclostrobin was observed in the gills and heart compared with accumulation in other tissues and gill tissue showed the most severe damage. Hypoxia symptoms (water jacking, tummy turning and cartwheel formation) in fish were observed throughout the experiment. Taken together, our results suggested that the gills are important target organs. The high pyraclostrobin toxicity to gills might be associated with oxidative damage to the gills, inducing alterations in ventilation frequency, oxygen-carrying substances in blood and disorders of energy metabolism. Our research facilitates a better understanding of the toxic mechanisms of pyraclostrobin in fish, which can promote the ecotoxicological research of agrochemicals on aquatic organisms.

Two farmed freshwater fish species Nile tilapia (Oreochromis niloticus) and jade perch (Scortum barcoo) were cultured with food waste-based diets and compared with commercial formulated control diet for a period of six months. Sixteen priority polycyclic aromatic hydrocarbons (PAHs) in the diets and cultured fish meat were tested by gas chromatography–mass spectrometry. No significant differences of ∑PAHs were observed between Nile tilapia and jade perch fed with food waste-based diets and control diet (p > 0.05). However, there were significantly higher concentration of ∑PAHs in market fish compared with the same species of fish fed by food waste-based diets (p < 0.05). Thus, the food waste-based diets have a potential to lower the PAH concentrations in farmed fish when compared with market fish. Based on the PAH concentrations, a human health risk assessment was made. The results indicated there were no non-cancer and very low cancer risks of consuming fish cultured with food waste-based diets at the 95th centile (Nile tilapia: hazard index (HI adult) = 0.343 × 10−3, HI children = 0.614 × 10−3 and cancer risk value = 0.943 × 10−6; jade perch: HI adult = 0.456 × 10−3, HI children = 0.814 × 10−3 and cancer risk value = 0.291 × 10−6). In general, the fish fed with food waste-based diets were unlikely to cause adverse health effects, based on the concentrations of PAHs. There is great potential for using food waste-based diets as an alternative to commercial feeds for cultivating freshwater fish.

The occurrence of microplastics was investigated in water, sediment and fish from the Fengshan River system. All collected samples contained microplastics with 334–1058 items/m³ in the water samples, 508-3987 items/kg dry weight in the sediment samples and 14–94 items/fish in the fish samples. The spatial distribution of microplastics in water and sediments was attributed to anthropogenic discharges, flow dynamics, tidal exchanges and microplastic density. This was evidenced by significant correlations of microplastics with the river pollution index (RPI), chemical oxygen demand (COD), suspended solid (SS), flow velocity and the presence of different polymer types of microplastics in water and sediment. Microplastic abundance in fish was correlated to SS, pH and conductivity, indicating that these water quality variables might affect bioavailability of microplastics to fish. Concentrations of microplastics/cm length of demersal fish at a higher trophic level (Leiognathus equulus and Pomadasys argenteus) were higher than those of a benthopelagic fish (Oreochromis niloticus niloticus). The significant relationships observed suggest that collected fish might prefer to ingest long fibrous microplastics from sediments and large fragmented microplastics from water. The high levels of 3- and 4-ring polycyclic aromatic hydrocarbons (PAHs), particularly fluoranthene and pyrene, in fish muscle revealed that the collected fish species might have a high ability to accumulate these PAHs from food and the environment. Significant relationships between some PAHs in fish and microplastic abundances in water/sediments/fish suggested that these PAHs might be accumulated by fish from contaminated microplastics. This study provides unique information on the factors influencing the spatial distribution of microplastics and the role of microplastics on the accumulation of PAHs by fish.

Antibiotics used in global aquaculture production cause various side effects, which impair fish health. However, the use of dietary composition such as carbohydrate, which is one of the dominant components in fish diets to attenuate the side effects induced by antibiotics, remains unclear. We determined the ability of high carbohydrate diet to protect Nile tilapia (Oreochromis niloticus) from oxytetracycline-induced side effects. Triplicate groups of thirty O. niloticus (9.50 ± 0.08 g) were fed on medium carbohydrate (MC; 335 g/kg) and high carbohydrate (HC; 455 g/kg) diets without and with 2.00 g/kg diet of oxytetracycline (80 mg/kg body weight/day) hereafter, MCO and HCO for 35 days. Thereafter, we assessed growth performance, hepatic nutrients composition and metabolism, microbiota abundance, immunity, oxidative and cellular stress, hepatotoxicity, lipid peroxidation and apoptosis. To understand the possible mechanism of carbohydrate protection on oxytetracycline, we assessed the binding effects and efficiencies of mixtures of medium and high starch with oxytetracycline as well as the MCO and HCO diets. The O. niloticus fed on the MCO and HCO diets had lower growth rate, nutrients utilization and survival rate than those fed on the MC and HC diets, respectively. Dietary HCO increased hepatosomatic index and hepatic protein content of O. niloticus than MCO diet. The O. niloticus fed on the HCO diet had lower mRNA expression of genes related to protein, glycogen and lipid metabolism compared to those fed on the MCO diet. Feeding O. niloticus on the HCO diet increased innate immunity and reduced pathogenic bacteria, pro-inflammation, hepatotoxicity, cellular stress and apoptosis than the MCO diet. The high starch with oxytetracycline and HCO diet had higher-oxytetracycline binding effects and efficiencies than the medium starch with oxytetracyline and MCO diet, respectively. Our study demonstrates that, high carbohydrate partially protects O. niloticus from oxytetracycline-induced side effects by binding the antibiotic. Incorporating high carbohydrate in diet formulation for omnivorous fish species alleviates some of the side effects caused by antibiotics.