Evaluation of oxygen changes on gill and spleen tissue of Caspian Sea Salmon (Salmo trutta caspius)

Caspian brown trout is one of the most valuable fishes in the Caspian Sea and has great value due to its marketability, appearance and taste of meat. This study was carried out to determine the effects of oxygen stresses on histopathology of gill and spleen in Caspian brown trout in Shahid Bahonar reproduction and breeding Center of Kelardasht in winter 2016. 210 fish with average weigh 50±10 gr were randomly selected and placed in tanks with aerator and oxygen capsule. Fish were divided into 3 treatments: treatment 1 or hypoxia (2-3 mg/l oxygen), treatment 2 or normoxia (7-8 mg/l oxygen) and treatment 3 or hyperoxia (12-14 mg/l oxygen) and each treatment had three replications. At the end of the experiment, sampling gill and spleen were performed for measuring histological injuries. Gill and spleen specimens were transferred to Inland Waters Aquaculture Research Center for histopathological examination. The results showed symptoms in all treatments, which included hemorrhage, clubbing or torsion of the lamella, epithelial hypertrophy, local and diffuse hyperplasia, necrosis, hyperemia, telangiectasia, lamella adhesion and the separated epithelium from lamella in gill and hyperemia, necrosis, vacuolation in the cytoplasm of cells, hemosiderin and sinusoids in spleen. In general, it can be said that the oxygen level of 7-8 mg/l is the most favorable condition for Caspian brown trout.