مطالعه مرگ و مير و بافت شناسي پوست لارو تازه تفريخ شده ماهي آزاد درياي خزر (salmo trutta caspius)، قرار گرفته در معرض اشعه UV-B

Skin Histology and Mortality of Salmo trutta caspius Newly Hatched Larvae Exposed to UV-B Radiation

Effects of UV-B radiation on skin structure and mortality was investigated in newly hatched larvae that were exposed to different doses of UV-B radiation (68.75 and 94. 83 jiw/cm2) for 15 minute (between 13:00-13:15) once a day in laboratory condition. Eggs without UV-B exposure served as control. Aquariums were covered with black plastic covers which prevented reception of any solar light by eggs and larvae. Period experiment continues 9 days. In both UV-B treatments, all of the larvae died within 9 days. No mortality was observed in control group. Mortality in days 1 to 6 was low but significantly increased during days7 to 9. In histological studies of UV-B treatments were observed that the number of mucus cells reduced as a caused by UV-B exposure in 1 to 5 days. We suggest that this decrease is due to secreting of mucus for protection again UV-B radiation, as result decrease in the its number, followed by increased at 7 days and again were decreased significantly in 8 and 9 days than early days. Their size was small. The number of mucous cells was reduced in control treatment. Alteration process of percentage of mucus-secreting cells in UV-B treatments were inverse the number of mucus cells alterations. Epidermis thickness also in UV-B treatments increased in 1 to 7 days and decreased in 8 and 9 days that was due to epidermis destroy. Epidermis thickness was increased in control treatment but this alteration was not significant in each treatments. Alterations among different treatments were not remarkable but there were significant difference between treatments and control. UV-B radiation also induced necrosis, sunburn cells and lifting epidermis from basal membrane and increased melanin pigments. Our results indicated that UV-B radiation has significant effects on survival rate, epidermal thickness, percentage of mucus secreting cells, necrosis, sunburn and melanin pigments. Four to six days assumed for the regeneration time of goblet cells in different fish species. In our experiment larvae have enough time to replace the mucus cells, but skin damages were so much that donʹt have compensate by mucus cells generation.