BACKGROUND: Intensive aquaculture, which is always associated with high concentrations of nitrogen pollu-tants, can lead to increased economic damage and energy loss, and increased fish mortality. OBJECTIVES: This study aimed to investigate the histomorphometry of the skin and stress indices of the Nile tilapia on exposure to different concentrations of ammonia. METHODS: In this study, Nile tilapia fingerlings were prepared and kept in the tub for adaptation, oxygenation, and feeding. A Range Finding test was performed on the fishes to find the ammonia killing range. Then, an acute toxicity test was performed on tilapia fish for 96 hours. For sub-lethal toxicity studies, 120 Nile tilapia fry were divided into 4 groups, including three groups based on different percentages of LC50 96 h (10, 20, and 30% LC50 96h) and a control group. The groups were exposed to ammonia for 14 days in an environment with constant tem-perature and pH control. Finally, histological examination and stress indices were performed on fish. RESULTS: The results showed that a higher concentration of ammonia resulted in tissue damage, including dis-coloration and skin blackening, and behavioral changes, including swallowing air from the water surface, decreased appetite and decreased mobility which finally resulted in death in these animals (P≤0.05). The highest and lowest glucose levels were reported for the control group and 2.7 mg/L. In addition, stress indices were significantly in-creased in experimental groups (P≤0.05). CONCLUSIONS: The data obtained from this study showed that increasing the amount of ammonia can lead to irreversible tissue damage to the structure of the skin and other tissues. In addition, the increase in oxidative stress in the Nile tilapia was due to the increase in ammonia, which led to lesions in these fish

Dermatophilosis is a bacterial skin infection and wet conditions like, raining and dipping predispose sheep to it. A great economic loss can be caused by this disease because of its effect on the quality of wool. In Iran (near Saveh), there was an outbreak of the disease in a herd and the clinical manifestation was different from that of typical dermatophilosis. Diffuse wide alopecic area accompanied by large amount of purulent discharges were seen. The main lesions were located at the thoracic area. Secondary infection caused by Pseudomonas aeruginosa and bacteremia caused by staphylococcus was diagnosed and is considered to be the cause of 0.16% mortality.For diagnosis blood samples were obtained for CBC, and bacteriological culture and direct smear were taken from skin lesions. Biopsy was also prepared from skin lesions for histopathologic study and bacteriologic culture. Direct microscopic examination was made on Giemsa-stained smear prepared from crusts and their underlying tissue. Gram stained smear  was also prepared from underlying crusts of skin. After bacteriological and histopathological evaluation, Dermatophilus was determined. A typical railroad track of Gram positive bacteria was seen in Gram and Giemsa stained smear.  Filamentous bacteria in the epidermis were seen in histopathological samples. Infection was controlled by treating herd intramuscularly with 70,000 mg/kg BW procaine penicillin G, twice daily for 5 consecutive days.