Aims and Background: Increasing use of nanomaterials in various sectors cause environmental concerns for humans and other organisms. Therefore, the purpose of this research was the effect of modified carbon nanotubes by dendrimer on the gill histopathology of Zebrafish (Danio rerio) under laboratory condition.

Methods and Materials: In this research, four concentration of carbon nanotubes non-lethal were used that the including 1, 10, 32, and 100 mg/l with the control group (no chemical). After 4 days exposure to carbon nanotubes, the samples of fish gill were taken. To study classical histology, after preparation of the samples with haematoxylin - eosin staining, the slides were photographed by an optical microscope.

Results: The results of this research indicated that the carbon nanotubes caused damages such as clubbing the head string, edema, hyperplasia, fusion, aneurysms, mucous, and necrosis in gills of zebra fish. Moreover, levels of tissue damages in gill on the carbon nanotubes were dose-dependent.  

Conclusion: according to results of this study, the damage levels of gill histopathology exposure to carbon nanotubes – dendrimer composite was more serious in high concentrations and there was no possibility of tissue recovery. The damages of this composite on gill tissue show the toxicity of this substance on zebrafish and recommended the release of this substance into the aquatic environment to be controlled.