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Common carp fish (Cyprinius carpio) is a native Asian and Eastern Europe, so there are many types of teleost fishes in Iraq. This study was designed to explain the environmental effects on the tissue of gills of fish. Twenty six of carp fish specimens were collected from Tigris River of Taji region in Baghdad city during Winter and Summer in January and August months respectively. Also the samples were collected from rearing aquarium by breeders of the fishes with water temperature recorded (31°C), in summer and (8 °C), in winter season via thermometer through the specimens collection in each time. The seasonal temperature levels were considered important in the histological alterations of the gills, where the present study showed high and low temperature degrees through Winter and Summer seasons and recorded histological changes in the gills such as (thickness of gill epithelium, rupture with hemorrhage of blood vessels), in summer season. The histological changes recorded in Winter season included damage and cellular atrophy of gill epithelium, fusion of gill secondary lamellae ends and lamellar disorganization with lifting of epithelial cells. The present study showed significant variance through gills epithelium P˂̲0.01 between two seasons, where statistical measurement showed that interlamellar distance significantly increased P˂̲ 0.01 during summer and winter significantly (P˂̲ 0.01) decreased in winter.