Different types of metal oxide nanoparticles (NPs) have been suggested for various applications such as water treatment and construction of agricultural pesticides; however, there are concerns about the potential toxicity of these compounds for the nontarget organism especially aquatic organisms. The aims of this study were assessing toxicity and histopathological effects of copper oxide NPs (NPs-CuO) on common carp (Cyprinus carpio) as a model organism. For this purpose 150 common carp with an average weight 7 ± 1 g were exposed to 0, 10, 20, 30, 40, 60, 80, 100, 150, and 200 mg/l of CuO-NPs (10 treatment with three replicates) for 96 hrs. After 24, 48, 72, and 96 hrs exposures, mortality rates recorded and gill samples were collected. Statistical analysis showed significant differences in carp survival between control and treatment groups (p < 0.05); regression between fish mortality rate and NPs-CuO concentration was also revealed (p < 0.01). The LC 96h of NPs-CuO for common carp was estimated as 124.9 mg/l in this study. Various tissue damages were observed in gill of treatments; such as, hypertrophy, hyperplasia, lamellar fusions, erythrocyte infiltration, epithelial lifting; also, there was significant correlation between intensity of tissue lesions and concentration of NPs-CuO (p < 0.01). The findings of the present study demonstrate that sublethal concentration of NPs-CuO can lead to serious tissue lesions. Whats more, concentrations above 30 ml/l of NPs-CuO can lead to some clinical signs; such as skin darkening and death with open mouth as well as definite fish death.

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The application of nanoparticles in various industries has grown significantly in recent years. The aims of this study were evaluation effects of silver nanoparticles (AgNPs) on survival rate and tissues (Gills) of Guppy (Poecilia reticulate) as a model of the freshwater organism. For this purpose, 90 mature fish were exposed to a different level of AgNPs for 96 hr. Data analyzed showed there was a significant correlation between fish mortality rate and AgNPs concentrations. Histological assays showed some typical tissue damages such as hyperplasia, hypertrophy, hyperemia, hemorrhage, and necrosis. Moreover, fish exposed to a lethal concentration of AgNPs showed some clinical signs, such as increasing operculum movement, swimming near the water surface, anxiety, and death with open mouth. The results of the present study showed that AgNPs can have toxicity effects on Guppy, also to sub-lethal concentrations, leading to several tissue damages and reduced survival rate of fish.

Pesticides can induce changes in behavior and reduce the survival chance of aquatic organisms. In this study, the toxic effects of glyphosate suspension (Glyphosate Aria 41% SL, Tehran Iran) on behavior and tissues of common carp (Cyprinus carpio) were assessed. For this purpose, a 96 h LC50 of glyphosate suspension (68.788 mL·L−1) was used in the toxicity test. All individuals were divided into control and treatment groups with four replicates. Exposure operations were performed under two conditions: increasing concentration of suspension from 0 to 68.788 mL·L−1; then, decreasing to the first level. The swimming pattern was recorded by digital cameras during the test and tissue samples were collected at the end of the test. There were significant differences between the swimming pattern of treated individuals and control ones during both steps. The sublethal concentration of glyphosate led to hypertrophy, hyperplasia and hyperemia in the gill of fish. However, changes were obvious only after sampling. The exposed fish also displayed clinical signs such as darkening of the skin and increasing movement of the operculum. Moreover, glyphosate suspension affected swimming patterns of fish suggest that the swimming behavior test can indicate the potential toxicity of environmental pollutants and be used as a noninvasive, useful method for managing environmental changes and assessing fish health conditions by video monitoring.