The wetland ecosystem (WE) is subject to pollution by many anthropogenic activities, including domestic and industrial effluents. These effluents may contain toxic heavy metals that can interact within the aquatic ecosystem and have a capacity to disturb the metabolic activities, histological profile, and genetic structure and functions in aquatic species inhabiting the environment. The present study observed the karyological and histological alterations in gills of the freshwater fish, Mozambique tilapia, Oreochromis mossambicus in two different sublethal concentrations (1% and 3%) of heavy metals in 7, 15, and 30 days of experimental periods. The heavy metals induced various structural damages such as ring chromosome, sister chromatid exchange, acrocentric association region, condensed chromosomal morphology, heterochromatin region, and nucleolar organizer region in the chromosomes of O. mossambicus treated with 1% and 3% sublethal concentrations of water sample collected from Pallikaranai wetland ecosystem. Gills exposed to 1% and 3% effluent exhibited several variations in the respiratory surfaces of gill arches or lamellae in the light and scanning microscopical study. The gills exposed to 1% concentration for 30 days showed marked necrosis, and the secondary lamellae showed the lamellar membrane's dissolution. Exposure of gills to raw effluent in the field condition was observed in the presence of Cd, Pb, Cr, Cu, and Zn. Thus, this present study shows the environmental deterioration by heavy metal pollution on the structure of the gills in tilapia.

The major aim of this study was to investigate heavy metal content of edible fish in the PRD. Eleven species of fish (consisting of 711 individuals) [catfish (Clarias fuscus), tilapia (Oreochromis mossambicus), grass carp (Ctenopharyngodon idellus), bighead carp (Aristichthys nobilis), mandarin fish (Siniperca kneri), snakehead (Channa asiatiea), black bass (Micropterus salmoides), mangrove snapper (Lutjanus griseus), star snapper (Lutjanu stellatus), snubnose pompano (Trachinotus blochii) and orange-spotted grouper (Epinephelus coioides)] were collected for the analyses of heavy metals. Overall concentrations (mg/kg, ww) in the fish muscles were: As (0.03–1.53), Pb (0.03–8.62), Cd (0.02–0.06), Ni (0.44–9.75), Zn (15.7–29.5), Cr (0.22–0.65), Cu (0.79–2.26), Mn (0.82–6.91). Significant level of Pb were found in tilapia at all locations. It is recommended that heavy metal concentrations in different fish species must be determined on a regular basis in the future so as to reduce human health risks from acute and chronic food intoxication.

This paper reports on the seasonal and species comparison of hepatic nodular alterations in two indicator fish species from the hyper-eutrophic Roodeplaat Dam in South Africa. This freshwater system is characterized by seasonal cyanobacterial algal blooms which release bio-toxins, including hepato-toxins, which can have negative effects on the health of the resident fish population. A total of 115 Clarias gariepinus (Burchell) and 98 Oreochromis mossambicus (Peters) were collected seasonally across six different surveys over a period of 3 years. Nodular alterations in livers were assessed both macroscopically and microscopically. We found a species difference with a 48% prevalence of nodular alterations in C. gariepinus and no macroscopically visible alterations in O. mossambicus. Affected fish also showed an increase in the ratio of liver mass to body mass, i.e., the hepatosomatic index. The microscopic characteristics of the nodules were primarily associated with pre-neoplastic, focal areas of cellular alterations; most prevalent were focal areas of steatosis. However, we could not establish a seasonal pattern regarding the occurrence of these alterations and therefore no association between the occurrence of the liver pathology and the cyanobacterial blooms. Our results therefore suggest that the occurrence of nodular alterations is not an acute, seasonal response, but rather a chronic, and possibly, and more interestingly, a species-specific, pathological response.

Invasive species exert a strong impact on the trophic structure and functioning of the ecosystem they occupy. A modeling software globally used to assess these impacts is Ecopath with Ecosim. This study measures the effects of two invasive species, African catfish Clarias gariepinus, in the food web of the Karapuzha reservoir ecosystem in India. The findings show that the two invasive species directly and indirectly influence several ecosystem elements. The high level of niche overlap (92%) and strong competition for similar resources was exhibited by C. gariepinus. The adverse effects of African catfish on all fish and crustaceans in the reservoir were revealed by mixed trophic impact. Oreochromis mossambicus impacts were both positive and negative. It had a beneficial impact on its predator aquatic birds and was negative towards minnows. This study will help fishery managers to make informed decisions for ecosystem-based fishery management of fish resources.

A study was carried out to assess the levels and effects of atrazine, dimethoate, and dichlorodiphenyltrichloroethane on freshwater fish (Oreochromis mossambicus). Water and fish were sampled once from a dam within the Hippo Valley A2 farmlands in Chiredzi, in the southeastern part of Zimbabwe. The samples were screened for atrazine, dimethoate, and dichlorodiphenyltrichloroethane (DDT), the pesticides commonly used in the region. Atrazine and dimethoate are pesticides commonly used in the control of weeds and pests in the agricultural production of sugarcane in Hippo Valley, Chiredzi region. The effects of the pesticides on biochemical endpoints of the sampled fish were determined. The analyzed biochemical end parameters were superoxide dismutase, catalase, glutathione S-transferase, and glutathione peroxidase activities in liver and white muscle fish extracts. Dichlorodiphenyltrichloroethane was observed in water and fish muscle tissue at concentrations of 131.3 μg/l and 171.7 μg/kg, respectively, while atrazine was detected at concentrations of 6.15 μg/l and 142.0 μg/kg in water and fish muscle tissue, respectively. The observed concentrations of atrazine and DDT in water samples were above the limits permissible by the World Health Organization in drinking water. Dimethoate was found in concentrations of 4.21 μg/l and 1.30 μg/kg in water and fish muscle tissue respectively. The observed concentration of dimethoate in water was below the acceptable limit set by the Guidelines for Canadian Drinking Water. Antioxidant enzyme activities were increased significantly (p < 0.05) in fish exposed to water from Hippo Valley, Chiredzi, when compared with the controls. The enhanced activities of the studied antioxidant enzyme system were attributed to exposure to pollutants in the water body. Alterations of the biochemical integrity of fish indicate negative effects of the pesticides on the well-being of fish and undoubtedly other aquatic biota as well.

Metal oxide nanoparticles are widely used in industries, and peak level can be confirmed in their surroundings. In the present study, the sub-lethal effects of CuO-NPs from low to high concentration as 0.5 to 1.5 mg/L were observed in tilapia (Oreochromis mossambicus). Accumulation of copper from CuO-NPs was increased with the increase in doses, and maximum accumulation was found in the gill than liver and muscles. The increased lipid peroxidation level was observed in the gill as compared to liver, and the similar results were obtained in catalase and glutathione while superoxide dismutase level was higher in the liver than gills. In histological alterations, gill edema, curved tips, fusion of gill lamellae, and thickening of primary and secondary gill lamellae were observed. Necrosis and apoptosis with condensed nuclear bodies and pyknotic nuclei were observed in the liver at the highest dose concentration. In a genotoxic study, the highest value of % tail DNA and olive tail movement was observed with increasing concentrations. Copper oxide nanoparticles has greater potential to accumulate in the soft tissues, which may cause respiratory distress such as oxidative stress, induction of antioxidant defense by raising glutathione, organ pathology, and genotoxicity.

Fluctuation exposure of trace metal copper (Cu) is ubiquitous in aquatic environments. The purpose of this study was to investigate the impacts of chronically pulsed exposure on biodynamics and subcellular partitioning of Cu in freshwater tilapia (Oreochromis mossambicus). Long-term 28-day pulsed Cu exposure experiments were performed to explore subcellular partitioning and toxicokinetics/toxicodynamics of Cu in tilapia. Subcellular partitioning linking with a metal influx scheme was used to estimate detoxification and elimination rates. A biotic ligand model-based damage assessment model was used to take into account environmental effects and biological mechanisms of Cu toxicity. We demonstrated that the probability causing 50% of susceptibility risk in response to pulse Cu exposure in generic Taiwan aquaculture ponds was ~33% of Cu in adverse physiologically associated, metabolically active pool, implicating no significant susceptibility risk for tilapia. We suggest that our integrated ecotoxicological models linking chronic exposure measurements with subcellular partitioning can facilitate a risk assessment framework that provides a predictive tool for preventive susceptibility reduction strategies for freshwater fish exposed to pulse metal stressors.

The purpose of this study was to link toxicokinetics/toxicodynamics (TK/TD) and bioavailability-based metal uptake kinetics to assess arsenic (As) uptake and bioaccumulation in three common farmed species of tilapia (Oreochromis mossambicus), milkfish (Chanos chanos), and freshwater clam (Corbicula fluminea). We developed a mechanistic framework by linking damage assessment model (DAM) and bioavailability-based Michaelis–Menten model for describing TK/TD and As uptake mechanisms. The proposed model was verified with published acute toxicity data. The estimated TK/TD parameters were used to simulate the relationship between bioavailable As uptake and susceptibility probability. The As toxicity was also evaluated based on a constructed elimination–recovery scheme. Absorption rate constants were estimated to be 0.025, 0.016, and 0.175 mL g−1 h−1 and As uptake rate constant estimates were 22.875, 63.125, and 788.318 ng g−1 h−1 for tilapia, milkfish, and freshwater clam, respectively. Here we showed that a potential trade-off between capacities of As elimination and damage recovery was found among three farmed species. Moreover, the susceptibility probability can also be estimated by the elimination–recovery relations. This study suggested that bioavailability-based uptake kinetics and TK/TD-based DAM could be integrated for assessing metal uptake and toxicity in aquatic organisms. This study is useful to quantitatively assess the complex environmental behavior of metal uptake and implicate to risk assessment of metals in aquaculture systems.

Many of South Africa’s freshwater impoundments are compromised by pesticide pollution, and the Roodeplaat Dam, near Pretoria, is no exception. This paper is, to the best of our knowledge, the first report of the herbicides Dacthal, metribuzin, simazine, tebuthiuron, terbuthylazine, and the fungicides azoxystrobin, carbendazim, epoxiconazole, metalaxyl (Ridomil), propiconazole, pyrimethanil and thiabendazole in a South African freshwater impoundment. This short note reports on the screening results of water and muscle tissue samples against a comprehensive library of pesticides, herbicides and fungicides in the polluted Roodeplaat Dam. Muscle samples of Oreochromis mossambicus screened positive for p,p'-DDE and p,p'-DDD and for DCPA (chlorthal-methyl). The muscle tissue of Clarias gariepinus screened positive for p,p'-DDE and p,p'-DDD, chlorpyrifos, trans-chlordane, DCPA and terbuthylazine. The presence of these pesticides, herbicides and fungicides in this impoundment is of great concern as there is substantial evidence of adverse health effects in fish exposed to these chemicals.