In this study which lasted from July 2020 to July 2022, 229 fish including 60 white fish, (Rutilus kutum) and 169 mullet of two species, Chelon auratus and Chelon saliens, were examined. Eight parasite species were isolated from white fish and six parasite species isolated from mullet. In this syudy, two monogenean species, Solostamenides mugilis and Ligophorus szidati, were identified for the first time from Narrow-nosed mullet in the Caspian Sea. The virology study by culture method on SSN1 cell line and IFAT test showed that VNN viral disease is still present in these fish as previous years but with less severity and can be one of the reasons for the scattered deaths of these fish. Aeromonas hydrophila and Pseudomonas aeruginosa bacteria contamination was detected in mullet fish samples and P. aeruginosa was detected in white fish. These bacteria are opportunistic bacteria and can cause disease and death in infected fish during stress. Abnormalities of organs were investigated by radiography, bone separation and histology. Although the amount of these Abnormalities is still limited in fish population; but it is warning about environmental pollution. Therefore, it is necessary to speed up the establish ment of sewage treatment plants to avoid the discharge of industrial, agricultural and domestic wastes in to water sources. Currently, one of the reasons for the decrease in catch in bony fish population is the loss of mullet due to VNN disease. Perhaps the pollution of coastal waters due to the entry of all kinds of sewage is also effective in moving fish. It seems that the main reason for the decrease in the amount of catch is the overfishing of non-standard fish in the past years.
Keywords: White fish; Mullet; Pathogens; Abnormality; Caspian Sea