Short-term exposure of Nile Tilapia (Oreochromis niloticus) to mercury: histopathological changes, mercury bioaccumulation, and protective role of metallothioneins in different exposure routes

Toxicity Evaluation, Oxidative, and Immune Responses of Mercury on Nile Tilapia: Modulatory Role of Dietary Nannochloropsis oculata

The current study evaluated the potential ameliorative effect of a dietary immune modulator, Nannochloropsis oculata microalga, on the mercuric chloride (HgCl2)-induced toxicity of Nile tilapia. Nile tilapia (45-50 g) were fed a control diet or exposed to ¼ LC50 of HgCl2 (0.3 mg/L) and fed on a medicated feed supplemented with N. oculata (5% and 10% (50 or 100 g/kg dry feed)) for 21 days. Growth and somatic indices, Hg2+ bioaccumulation in muscles, and serum acetylcholinesterase (AChE) activity were investigated. Antioxidant and stress-related gene expression analyses were carried out in gills and intestines. Histopathological examinations of gills and intestines were performed to monitor the traits associated with Hg2+ toxicity or refer to detoxification. Hg2+ toxicity led to significant musculature bioaccumulation, inhibited AChE activity, downregulated genes related to antioxidants and stress, and elicited histopathological changes in the gills and intestine. Supplementation with N. oculata at 10% was able to upregulate the anti-oxidative-related genes while downregulated the stress apoptotic genes in gills and intestines compared to the unexposed group. In addition, minor to no histopathological traits were detected in the gills and intestines of the N. oculata-supplemented diets. Our data showed the benefit of dietary N. oculata in suppressing Hg2+ toxicity, which might support its efficacy as therapeutic/preventive agent to overcome environmental heavy metal pollution in aquatic habitats.

Risk Assessment and Hazardous Effects of Metal Contamination in O. niloticus and S. galilaeus from Four Islands of the River Nile

The Nile River islands are recognized as the most productive lands in Egypt. Although, these islands are vulnerable to several natural and man-made crises. The present study was aimed to evaluate the consequences of different anthropogenic activities on the heavy metals load and histological alterations in O. niloticus and S. galilaeus collected from four different Nile River islands along the Great Cairo sector (Egypt), and the possible health risks for human consumers. Metals were accumulated in both fish muscles in the following order: Fe > Zn > Cu > Mn > Pb. S. galilaeus was recorded higher metal pollution index than O. niloticus, while El-Warrak Island was documented the highest MPI and hazard quotient among all sampling sites. All sampled tissues were recorded histopathological lesions in both fish. The present study may be considered as an early alert for habitual consumers, particularly at high consumption rates of some fish species.

Hepatotoxic effects of silver nanoparticles on Clarias gariepinus; Biochemical, histopathological, and histochemical studies

The current study investigates the hepatotoxic effects of two acute doses of silver nanoparticles (AgNPs) and silver nitrate (AgNO3) on African catfish (Clarias garepinus) using biochemical, histopathological, and histochemical changes and the determination of silver in liver tissue as biomarkers. AgNPs-induced impacts were recorded in some of these characteristics based on their size (20 and 40 nm) and their concentration (10 and 100 μg/L). Concentrations of liver enzymes (Aspartic aminotransferase; AST, Alanine aminotransferase; ALT), alkaline phosphatase (ALP), total lipids (Tl), Glucose (Glu) and Ag-concentration in liver tissue exhibited a significant increase under stress in all exposed groups compared to the control group. The total proteins (Tp), albumin (Al), and globulin (Gl) concentrations exhibited significantly decrease in all treated groups compared to the control group. At tissue and cell levels, histopathological changes were observed. These changes include proliferation of hepatocytes, infiltrations of inflammatory cells, pyknotic nuclei, cytoplasmic vaculation, melanomacrophages aggregation, dilation in the blood vessel, hepatic necrosis, rupture of the wall of the central vein, and apoptotic cells in the liver of AgNPs-exposed fish. As well as the depletion of glycogen content in the liver (feeble magenta coloration) was observed. The size and number of melanomacrophage centers (MMCs) in liver tissue showed highly significant difference in all exposed groups compared to the control group. Recovery period for 15 days led to improved most alterations in the biochemical, histopathological, and histochemical parameters induced by AgNPs and AgNO3. In conclusion, one can assume liver sensitivity of C. garepinus for AgNPs and the recovery period is a must.

Tracing Dietary Mercury Histochemically, with Autometallography, through the Liver to the Ovaries and Spawned Eggs of the Spot, a Temperate Coastal Marine Fish

Exposure to mercury (Hg) results in reproductive abnormalities and deficiencies in female fish. We traced the maternal assimilation and redistribution of dietary inorganic (HgII) and organic (MeHg) forms of Hg in a coastal marine fish, the Spot Leiostomus xanthurus. We conducted a 90-d laboratory experiment in which treatment Spot were fed muscle of Blue Marlin Makaira nigricans with elevated concentrations of Hg mixed with a commercial fish food, while control Spot were fed only commercial food pellets. Gonadal maturation was induced by shortening the photoperiod and increasing the temperature. Spawning was induced by intramuscular injection of human chorionic gonadotropin at 100 IU/kg. Solid-sampling atomic absorption spectrophotometry measured the total Hg (THg), HgII, and MeHg in Blue Marlin muscle. Autometallography located Hg-sulfide granules in the liver, ovaries, and spawned eggs, and densitometry provided comparisons of Hg-sulfide granules in the ovaries of treatment and control Spot. Overall, the intensity and prevalence of Hg-sulfide granules were greater in the liver, ovaries, and eggs from treatment Spot than in those from controls. The tissue and cellular distribution of Hg-sulfide granules differed. Received November 18, 2016; accepted June 18, 2017.

Melanomacrophage centers in Clarias gariepinus as an immunological biomarker for toxicity of silver nanoparticles

Although there are many applications of silver nanoparticles (Ag-NPs) in human activities, there is still little known about their potential environmental toxicity, particularly to fish. In the present study, the effects of Ag-NPs on African catfish (Clarias gariepinus) were studied using melanomacrophage centers as immunohistological biomarkers. Fish were exposed to 25 mg/L, 50 mg/L and 75 mg/L 100-nm Ag-NPs. We studied the effects on the size and number of melanomacrophage centers in all target tissues. Many histopathological alterations in those tissues were observed. The histological changes were represented as dislocation of the epithelium, dilatation of central veins associated with inflammatory leukocytic infiltration, necrosis, and pyknotic nuclei of hepatocytes. There was shrinkage of Malpighian corpuscles, dislocation of nuclei of convoluted tubules, cellular degeneration, and dispersed infiltration of leukocytes in kidney tissue. Examination of spleen sections after exposure to Ag-NPs showed rupture within the red pulp and hemorrhage, dislocation of nuclei, accumulation of inflammatory leukocytes, and congestion in blood vessels. In conclusion, exposure to Ag-NPs induced alterations in tissues, suggesting a possible increase in oxidative stress in those tissues.

Use of histopathology and elemental accumulation in different organs of two benthophagous fish species as indicators of river pollution

The bottom feeding fish species have a good potential to be used for assessments of pollution, as they are under pressure from pollutants from both water and sediments. In this study, the level of similarity of histopathological responses to pollution in gills and liver between barbel (Barbus barbus) and sterlet (Acipenser ruthenus) from the Danube River was assessed, and compared with elemental concentrations in their gills, liver, and muscle. Results indicate that the detected metal concentrations were likely cause of different tissue responses in gills and liver of the two investigated fish species. Statistical analysis indicated a clear differentiation of the two species based on elemental concentrations and the level of histopathological changes in gills and liver. Metal concentrations exceeded maximum acceptable concentrations in a number of analyzed specimens, which indicates the importance of this type of monitoring. Results indicate that barbel is a better indicator for specific, rather narrow sites, whereas sterlet is a better indicator of larger (longer) water current segments. Obtained information could be of importance for both scientists and fishery and water management authorities working on the development of water monitoring programs.

Molecular evolution of the Slc15 family and its response to waterborne copper and mercury exposure in tilapia

The solute carrier 15 family (Slc15), also called oligopeptide transporter family (Pept), was well-known for its role in the cellular uptake of di/tripeptides and peptide-like molecules. Our understanding of Slc15 family has already been enlarged since the rapid increasing of genome information; however, efforts are still expected to reveal the diversification of the family in an evolutionary manner. In the study, the sequence information were collected and analyzed through eleven eukaryotic organism representatives, especially in fish species. Gene expansion was observed through the evolution of the family. Further study was carried out with the representative species-Nile tilapia (Oreochromis niloticus). Tissue expression profiles were compared among members of the Slc15 family. Generally, they were all highly expressed both in the intestine and stomach, however, different members possessed its special tissue expression pattern. The mRNA levels of all the members (except Slc15a4) decreased after fasting while refeeding could restore the expression level. The recovery ability was impaired after exposure to environmental relevant concentration of copper (Cu(2+), 160 nmol/L). By contrast, mercury (Hg(2+), 25 nmol/L) did not exert significant impact on the recovery ability.