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The acute toxicity and histopathology of Schizothorax zarudnyi  (2±0.2 g body weight)exposed to diazinon was assessed statically in 22±2°C, following the OECD Guideline. The 96h LC50 value of diazinon for the fish was 14.70 mg/l, therefore making its MAC value 1.47 mg/l in natural waters. According to the table of insecticides sorting, the toxicity of diazinon was low for S. zarudnyi. Some clinical symptoms and abnormal reactions such as lordosis and neural paralytic syndrome, losing the balance and swimming in a half circle, expressive pigmentation mainly on the dorsal part and block of respiration movements in the fish exposed to this pesticide were observed. Histopathological evidence from the tissues of liver, kidney, gill, and gut revealed vascular tissue of the liver, sinusoids, hepatocytes vacuole degeneration, shrinkage and degeneration of some urinary cells, dilatation of Bowman's space, pycnotic nucleus of some kidney cells and increase in the number of interstitial kidney cells. Complications, such as hyperemia, telangiectasia, edema, shrinkage, clubbing and adhesion to the secondary gill filaments were also observed.

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Protein compounds were extracted from the mucus of sea anemone, Stichodactyla haddoni, and their effects on the gills of rainbow trout, Oncorhynchus mykisswere examined. Sea anemone samples were collected from the intertidal zone of the eastern coast of Hormuz Islandand frozen samples were transported to the laboratory. Then the mucus was extracted using of the PBS solvent and doses of 5, 10 and 24 mg/dry weight of total protein was injected into the tail vein of the fish. Upon the inactivation of fish, histopathological changes were examined using of the classical histological method. Lethal signs were observed in the gills, including aneurysm, hypertrophy of epithelial cells, lamella clubbing and deformation, subepithelial edema, lamella congestion in the interlamellar region and necrosis. The damages were more serious with increasing doses. The results showed that protein compositions of the mucus can cause numerous lesions in the gill tissue of fish, which act as an excretory, respiratory and ionic regulation tissue, the failure of which can lead to failure of fish’s vital functions that can be one of the reasons for the death of the hunted fish.  The results showed that the protein compositions of mucus can cause numerous lesions in the gill tissue, as an excretory, respiratory and ionic regulation tissue lead to failure of it functions that itself can be one of the reasons hunted fish death.

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The accumulation of nanoparticles in the environment and aquatic ecosystems due to their wide application in industries, agriculture, medicine and pharmaceuticals has caused an increasing concern about the environment and increasing exposure to nanoparticles in ecosystems and humans. Iron oxide nanoparticles easily enter the bloodstream, accumulate in different tissues and cause damage to these tissues. Therefore, in this research, changes in the intestinal tissue of gray mullet fish (M. cephalus) and tissue accumulation in oral exposure to iron oxide nanoparticles were investigated.
110 pieces of young gray mullet after 2 weeks of adaptation were treated in four-time groups of 1, 7, 14 and 28 days, and one group was considered as a control. The mullet fish received iron oxide nanoparticles twice a day at the rate of 15 mg/kg attached to the food. The results showed that although the amount of tissue iron increased significantly only in the 28-day group, the consumption of iron oxide nanoparticles in almost all groups increases the tissue accumulation of iron in the intestine. The intestinal histological study showed changes such as the increase in the number and size of goblet cells, destruction of microvilli structure, bleeding and degrees of necrosis, and the intensity and extent of the changes in the intestinal tissue increased with increasing exposure time.
These observations showed that the consumption of iron oxide nanoparticles has a negative effect on intestinal function and causes iron accumulation and the occurrence of time-dependent injuries.