The possibility of VNN occurrence and the effects of nervous necrosis virus (NNV) on immunological and histopathological changes in Caspian Sea salmon (Salmo trutta caspius) fingerlings fed by Chlorella vulgaris

This study evaluated the possibility of VNN occurrence and the effects of Chlorella vulgaris on immune parameters before and after exposure to Viral Nervous Necrosis virus in Caspian Sea salmon (Salmo trutta caspius). Fish were divided into 4 treatments with three replicates. Treatments included one control group and three experimental groups (T1, T2 and T3).  Fish in control group, T1, T2 and T3 were fed by diet supplemented with 0, 1×108, 2×107 and 3×106 Cell/ml chlorella/450 g food respectively, for 8 weeks. Blood samples were collected to calculate immune parameters (IgM, C3, C4, Total protein, respiratory burst, Albumin and Lysozyme). In addition, NNV supernatant was used for virus challenge in Caspian Sea in all treatments. Fish were monitored for 14 days to examine the supernatant pathogenesis and measure the changes in immune parameters after challenge with virus. RT-PCR, nested-PCR, IFAT, IHC tests, cell culture and histopathology examinations were also carried out. Results showed that S. trutta caspius fingerlings were resistant against NNV, so that no virus was observed in fish brain and eye tissues in all treatments. Moreover,Ch. vulgaris stimulated the  immune system of S. trutta caspius probably due to the compositions such as carotenoid pigment and different kind of vitamins in this microalga.