The Pangani catchment of Northern Tanzania harbours the critically endangered endemic tilapias of the genus Oreochromis. The introduction of non-native congenerics and consequent hybridization complicates taxa identification and phylogeny based on morphological systematics. We therefore morphologically and molecularly identified these tilapias and delimited their Molecular Operational Taxonomic Units (MOTUs) based on Cytochrome Oxidase Subunit I (CO1) gene for future management and conservation. A total of 132 indigenous and introduced tilapia specimens were morphologically identified, barcoded using the CO1 gene and delimited by Kimura 2 Parameter distance approaches, Automatic Barcode Gap Discovery (ABGD), Neighbour Joining (NJ) tree and haplotype analysis. Theoverall mean conspecific, congeneric and confamillial genetic distances based on the K2P model were 0.54%, 5.32% and 13.29% respectively. All taxa had a mean K2P distance < 2% and 90% (n = 10), were clearly delimited by the ABGD method. The NJ tree delimited tilapia taxa commensurate to the genetic distances depicted by DNA barcoding. However, DNA barcoding and NJ tree coherently failed to discriminate the morphologically distinct allopatric Oreochromis jipe and Oreochromis hunteri taxa. Moreover, the two methods depicted lack of monophyly in Oreochromis korogwe MOTUs implying that the taxon could consist of at least one MOTU. We conclude that the integration of morphological-based taxonomy and DNA barcoding among ichthyofaunal taxa herein will be invaluable in conservation and management of native tilapias in Pangani basin.

The present study described the most recent findings concerning the abundance and distribution of plastic in water, sediment, and fauna in the Nile River of Upper Egypt as an interesting research point. The findings revealed that plastics were abundant in the water, sediments, fish, and crayfish throughout the sites. The Nagaa Hammadi site has the highest abundance of meso- and macroplastics in its water and sediment. African catfish had the highest abundance of meso- and macroplastics compared to the other species, while Nile tilapia had no meso- or macroplastics in its alimentary canal or gills in all sites. The Edfu site has the highest abundance of mesoplastics in the alimentary canals of African catfish, while the Nagaa Hammadi site has the highest abundance of mesoplastics in the gills, and macroplastics appeared only in the alimentary canal of African catfish from the El-wasta site. Only mesoplastics were found in the crayfish\'s alimentary canal, with the Nagaa Hammadi site having the highest abundance. No macroplastics were detected in the crayfish\'s gills or alimentary canal. Additionally, this work lets us understand how plastics behave in freshwater environments, and it is a step toward decision-makers taking appropriate measures to reduce their risk.

Pesticide use has increased in the Lake Tana sub-basin due to increased agricultural activity, potentially endangering nontargeted organisms. To assess its potential impact on fish health and fish-consuming human populations, pesticide concentrations in the fillet and liver tissue of three fish species, namely Labeobarbus megastoma, Labeobarbus tsanensis, and Oreochromis niloticus, were investigated in Lake Tana. Fish samples were taken from the lake near the rivers of Ribb and Gumara, which flow through agricultural areas where considerable amounts of pesticides have been applied. A total of 96 fish samples were collected. Liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) revealed the presence of ten pesticides. Pyrimethanil was frequently detected in 96% of liver and 65% of fillet samples at a median concentration of 33.9 µg kg-1 and 19.7 µg kg-1, respectively. The highest concentration of pyrimethanil was found in L. megastoma (1850.0 µg kg-1). Labeobarbus megastoma also had the highest concentration of oxamyl (507.0 µg kg-1) and flazasulfuron (60.1 µg kg-1) detected in the liver tissue. The highest concentration of carbaryl (56.5 µg kg-1) was found in the liver tissue of O. niloticus. Fish tissue samples from the two study sites contained pyrimethanil, oxamyl, carbaryl, and flazasulfuron. Only pyrimethanil showed a statistically significant difference between the two sites and the species L. megastoma and L. tsanensis. The amounts of pesticides found in the fish species pose no direct risk to the health of fish consumer human population. However, the results show that the lake ecosystem needs immediate attention and regular monitoring of the rising pesticide usage in the lake watershed.

Anthropogenic pollution by trace metals in aquatic environments in semiarid zones is a critical area of investigation. The objective of this study was to investigate the concentration and spatial distribution of trace metals in surface sediments in the Rosário reservoir, which is affected by the intensive aquaculture of Tilápia-do-Nilo (Oreochromis niloticus). Sediment samples were collected in three different areas, postculture (PCTV), cultivation (CTV) and control (CTRL) in the dry season in 2019. The granulometric composition, organic matter and concentrations of Fe, Mn, Zn, Cu, Cr, Cd, Pb and Ni metals were determined. Multivariate statistics were used. Geochemical and ecotoxicological indices and a comparison with sediment quality guidelines (SQG) were used. The sediment was characterized by silty clay loam with an average organic matter of 18.76 ± 4.27. The analytical merit figures demonstrated accuracy (metal recoveries in certified standards) between 89 to 99% and high precision (RSD < 5%). The concentration ranges for the metals were Fe: 0.11-0.85 (%), Mn: 14.46-86.91, Zn: 2.6-220.56, Cu: 26.89-98.75, Cr: 60.18-76.06, Cd: 0.38-0.59, Pb: 18.13-43.13, and Ni: 34.4-46.75, all in (mg/kg-1). The highest concentration values were found in the CTV areas (Fe: 40 ± 0.22, Mn: 66.48 ± 19.11, Zn: 114.83 ± 59.75 and Cr: 70.85 ± 2.62) and PCTV (Cd: 0.53 ± 0.04, Cu: 71.83 ± 21.20, Pb: 33.71 ± 4.34 and Ni: 44.60 ± 1.79). Pearson\'s correlation, hierarchical cluster analysis and principal component analysis confirmed the influence of fish farming on metals. Only Ni presented concentration values higher than the reference value established in the SQG. Thus, considering the probable geochemical and ecotoxicological effects, they comprise the two lowest levels of impact.

Cichlid fish of the genus Oreochromis form the basis of the global tilapia aquaculture and fisheries industries. Broodstocks for aquaculture are often collected from wild populations, which in Africa may be from locations containing multiple Oreochromis species. However, many species are difficult to distinguish morphologically, hampering efforts to maintain good quality farmed strains. Additionally, non-native farmed tilapia populations are known to be widely distributed across Africa and to hybridize with native Oreochromis species, which themselves are important for capture fisheries. The morphological identification of these hybrids is particularly unreliable. Here, we describe the development of a single nucleotide polymorphism (SNP) genotyping panel from whole-genome resequencing data that enables targeted species identification in Tanzania. We demonstrate that an optimized panel of 96 genome-wide SNPs based on FST outliers performs comparably to whole genome resequencing in distinguishing species and identifying hybrids. We also show this panel outperforms microsatellite-based and phenotype-based classification methods. Case studies indicate several locations where introduced aquaculture species have become established in the wild, threatening native Oreochromis species. The novel SNP markers identified here represent an important resource for assessing broodstock purity in hatcheries and helping to conserve unique endemic biodiversity.

This study investigated the heavy metal and hydrocarbon pollution status of Orashi River in four communities of Imo and Anambra States of Nigeria. Water and fish (Oreochromis niloticus and Clarias gariepinus) samples were collected from the river in the dry and wet seasons. Hydrocarbon and physicochemical parameters were determined in water with standard methods. Water and fish muscles were digested and analysed for metals using atomic absorption spectrophotometry. Results of analyses indicated hydrocarbon pollution. Hardness, alkalinity, nitrate, chloride, phosphate, and sulphate were significantly higher (p < 0.05) in wet season samples. Arsenic was undetected in water samples, but higher cadmium and iron concentrations were recorded in the wet season samples. Lead concentrations in the wet season were higher at some sites than the World Health Organization guideline. Arsenic was detected in Clarias at three sites in both seasons, but iron concentrations were significantly higher (p < 0.05) than those of other metals. Lead concentrations in Clarias gariepinus were lower than the Codex limit (0.3 mg/kg) except in the muscle samples from four sites. Arsenic was undetected in Oreochromis niloticus muscle samples but concentrations for lead (0.851 ± 0.203-8.604 ± 1.264 mg/kg (dry season) and 0.627 ± 0.035-9.364 ± 0.786 mg/kg (wet season)) exceeded the Codex limits in all samples. Health risk indices for the species indicated potential risk to the population from the consumption of Oreochromis niloticus. However, hazard index and target carcinogenic risk values indicate that people in the communities do not face significant non-carcinogenic and carcinogenic risks from cadmium and lead intake by consuming the fish species.

Oreochromis fishes exhibit variability of sex-determination (SD) genes whose characterization contributes to understanding of the sex differentiation network, and to effective tilapia farming, which requires all-male culture. However, O. niloticus (On) amh is the only master-key regulator (MKR) of SD that has been mapped (XY/XX SD-system on LG23). In O. aureus (Oa), LG3 controls a WZ/ZZ SD-system that has recently been delimited to 9.2 Mbp, with an embedded interval rich with female-specific variation, harboring two paics genes and banf2. Developing genetic markers within this interval and using a hybrid Oa stock that demonstrates no recombination repression in LG3, we mapped the critical SD region to 235 Kbp on the orthologous On physical map (p < 1.5 × 10-26). DNA-seq assembly and peak-proportion analysis of variation based on Sanger chromatograms allowed the characterization of copy-number variation (CNV) of banf2. Oa males had three exons capable of encoding 90-amino-acid polypeptides, yet in Oa females, we found an extra copy with an 89-amino-acid polypeptide and three non-conservative amino acid substitutions, designated as banf2w. CNV analysis suggested the existence of two to five copies of banf2 in diploidic Cichlidae. Disrupting the Hardy-Weinberg equilibrium (p < 4.2 × 10-3), banf2w was concordant with female determination in Oa and in three cichlids with LG3 WZ/ZZ SD-systems (O. tanganicae, O. hornorum and Pelmatolapia mariae). Furthermore, exclusive RNA-seq expression in Oa females strengthened the candidacy of banf2w as the long-sought LG3 SD MKR. As banf genes mediate nuclear assembly, chromatin organization, gene expression and gonad development, banf2w may play a fundamental role inducing female nucleus formation that is essential for WZ/ZZ SD.

Fish gelatin and its hydrolysates exhibit a variety of biological characteristics, which include antihypertensive and antioxidant properties. In this study, fish gelatins were extracted from extrusion-pretreated tilapia scales, and then subjected to analyses to determine the physicochemical properties and antioxidant activity of the extracted gelatins. Our findings indicate that TSG2 (preconditioned with 1.26% citric acid) possessed the greatest extraction yield, as well as higher antioxidant activities compared with the other extracted gelatins. Hence, TSG2 was subjected to further hydrolyzation using different proteases and ultrafiltration conditions, which yielded four gelatin hydrolysates: TSGH1, TSGH2, TSGH3, and TSGH4. The results showed that TSGH4 (Pepsin + Pancreatin and ultrafiltration < 3000 Da) had a higher yield and greater antioxidant activity in comparison with the other gelatin hydrolysates. As such, TSGH4 was subjected to further fractionation using a Superdex peptide column and two-stage reverse-phase column HPLC chromatography, yielding a subfraction TSGH4-6-2-b, which possessed the highest 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging activity compared with the other fractions. Further LC-ESI/MS/MS analysis of TSGH4-6-2-b suggested two novel peptides (GYDEY and EPGKSGEQGAPGEAGAP), which could have potential as naturally-occurring peptides with antioxidant properties. These promising results suggest that these antioxidant peptides could have applications in food products, nutraceuticals, and cosmetics.

The demand for healthier foods with high nutritional value has resulted in intensive fish farming. In this production system, high-frequency infections occur, and antibiotics are administrated for control. Only two antibiotics are allowed for use in Brazilian aquaculture, one of which is florfenicol. In this work, a bioconcentration assay was performed to assess the accumulation of florfenicol in the muscle of Nile tilapia (Oreochromis niloticus). Tilapia was evaluated as it is the most produced fish species in Brazil. The fish were exposed to florfenicol at a nominal concentration of 10 mg/L, through the water. Muscle and water were collected at 0, 1.5, 3, 6, 24, and 48 h during the exposure phase and at 1.5, 3, 6, 24, 48, and 120 h during the depuration phase. Quantification was performed using an LC-MS/MS. The results showed rapid absorption and elimination of the antibiotic (half-life, t1/2 = 5 h), with low potential for accumulation of florfenicol in tilapia muscles. The study was performed to determine the bioconcentration factor (BCF) and withdrawal period of florfenicol, being 0.05 mL/μg and 1.8 h, respectively. The results contribute to set protocols for the safe use of florfenicol in tilapia transport, avoiding residues in fish that may pose risks to human health.

The current investigation pointed to report the negative impacts of silver nanoparticles [Ag]NPs that synthesized by leaf extract of Moringa oleifera on oxidative stress biomarkers of Oreochromis niloticus, as well as the role of different Selenium type to antagonistic that toxicity. Fish were exposed to [Ag]NPs (1.95 and 3.9 ppm) as sublethal concentrations alongside 0.1 ppm of Se bulk and 0.1 ppm biosynthesized [Se]NPs selenium nanoparticles antagonistic effect for 2 and 4 weeks. Lipid peroxidation (LPO), DNA fragmentation, total antioxidant capacity (TAOC), catalase (CAT), and superoxide dismutase (SOD) were evaluated as oxidative stress biomarkers,. A significant increase (p < 0.05) in LPO and DNA fragmentation and a significant decrease (p < 0.05) in TAOC, CAT, and SOD were found in [Ag]NPs exposed groups when compared with the control one. Biosynthesized [Se]NPs and Se bulk showed a positive role in [Ag]NPs detoxification. Our investigation suggested that [Ag]NPs showed a toxic effect on oxidative stress biomarkers. However, Se-NP addition gives a good recovery of oxidative biomarkers more than Se bulk in detoxification of [Ag]NPs.