effect of salinity as environmental factors on growth and intestine morphologi of caspian white fish(cyprinidae:rutilus frisii kutum)

the purpose of this experiment was to evaluate the effects of salinity on growth parameters and intestine morphology of the caspian white fish. experiment were used with four treatments include,(freshwater (0ppt), brackish water (5ppt), abrupt transition of fish to the salt water 10ppt: )the fish were transferred from fresh water to salt water immediately) and gradual transition of fish to the salt water10ppt )the fish were transferred from fresh water to brackish water for 12 hours and then saltwater) over 144 fishes with an average weight of 532± 0.005 mg. intestinal samples were divided into three parts: anterior, middle and posterior intestine and each sample were prepared and fixed. results showed that in all three sections of the small intestine villi brackish water treatment have had most size and there are significant difference with the treatment of freshwater and gradual transition of fish to the salt water(p