Histopathological study of gill in common carp (Cyprinus carpio) and goldfish (Carassius auratus) during exposure to lethal concentrations of nano-zinc oxide, nano copper oxide and nano titanium dioxide

Apart from skin, gills are the first place of direct exposure of fish to toxins or pollutants therefore study of changes in gill structure is a suitable indicator of toxins or pollutants under stressful conditions. The aim of this study was to investigate pathological alterations of gill tissue in common carp during exposure to different nanoparticles. For this study, 210 fry common carp with a total length of 7.36±0.30 cm and goldfish with a total length of 6.50±0.43 cm in 6 treatments with 3 replicates in each treatment were placed in 60 liter aquariums in groups of 11 individuals. Gill tissue samples of common carp and goldfish were taken 7 days after exposure to 50% lethal concentration of nano-zinc oxide, nano copper oxide and titanium dioxide nanoparticles. Histological changes were evident in samples exposed to nano-zinc oxide, nano copper oxide and titanium dioxide nanoparticles while no detectable changes were observed in control gill. The symptoms observed in both fish consisted of gill hyperplasia, adhesion of secondary lamellae, increased levels of mucus and hyperemia. The most common complication observed was gill hyperplasia and an increase in the amount of mucus. The results of this study indicate that 50% lethal concentration of nanoparticles of titanium, copper and zinc can cause tissue damage and destruction. Also, sub-lethal toxicity of nano-zinc oxide is higher than nano copper oxide and nano titanium dioxide and causes much wider effects on gill tissue of common carp and goldfish.