Background: Due to the multifactorial etiology, tumor manifestation in any vertebrate species may become a critical issue. This topic requires more consideration for species in aquatic ecosystems as an enclosed habitat. In addition, knowledge about oncogenesis in the aquaculture industry enhances the quality of products and its earned benefits.Objectives: This study investigated the tumor lesions, their characteristics, and probable causes, in the most commercially important fish in the southern Caspian Sea: Caspian white fish (Rutilus kutum). Methods: To accomplish this goal, after gross pathology of more than 20 cases, histopathological examinations and electron microscopic assays were employed.  Results: The findings confirmed squamous cell carcinoma and squamous cell papilloma in the examined cases. Furthermore, the virus-like particles were clearly observed in the transmission electron microscopy results, indicating the probable viral etiology for these neoplastic lesions in Caspian Kutum. Conclusion: This study is the first to report the tumor prevalence in fish species of the southern Caspian Sea, which could be an alert for the mentioned ecosystem’s health and the whole aquaculture industry.

BACKGROUND: Members of the genus Gyrodactylus species are one of the extensive groups of monogenean ectoparasites which parasitize marine, brackish and freshwater fishes. OBJECTIVES: The main objective of the present study is the identification and diagnosis of the Gyrodactylus specsies on the fishes in certain rivers in the southwest of the Caspian Sea basin. METHODS: The field investigations were carried out from March 2015 to June 2016 and approximately, 1240 fish specimens belonging to two families, nine genera and nine species from Babolrud, Tajan, Shirud, Tonekabon, Nekarud, Siahrud, Telar and Haraz rivers were examined. RESULTS: At least eleven Gyrodactylus species were isolated from skin and gills of the examined fishes. Among them, Gyrodactylus mutabilitas, G. sprostonae and G. prostae have been previously reported to be found in Iran. The rest, including Gyrodactylus ctenopharyngodonis, G. gobioninum, G. katharineri, G. nemachili, G. proterorhini, G. ophiocephali, G. varicorhini and G. vimbi are reported for the first time from Iranian Fishes. A tissue-specific microenvironment is seen in infection with Grodactylus proterorhini which was isolated from the gills, but mostly from the surface of the skin of Neogobius pallasi which is mainly specific to the brackish water of estuaries and coastal area. CONCLUSIONS: The host spectrum of Gyrodactylus species in Iran is actually wider and the further research may demonstrate that classification of individual species in terms of their host specificity will have to be changed and additional species of Gyrodactylus species would be found.

BACKGROUND: Hematological studies are valuable diagnostictechniques in the medical care of fish, reflecting the healthcondition and the effects of environmental factors on fish. OBJECTIVES:Due to the high value of sturgeon fish and necessityto recover the brood stock, this study was done to provide dataabout hematological parameters and reproduction normative ofwild brood stock beluga, Huso huso, from the southeast of theCaspian Sea. METHODS: Hematological parameters includingRBC, WBC, hematocrit, hemoglobin, MCV, MCH, MCHC,and differential leukocyte count were determined. In this regard,7 male and 7 female wild broods were studied. Differencesin mentioned parameters between genders were evaluated.The correlations among parameters were also determined.RESULTS: According to the results, the male fish had significantlyhigher WBC and lymphocyte and lower neutrophil comparedto the females. Also, functional fecundity was 447000 ±157210 and weight of extracted oocytes was 35.4 ± 3.78 mg/cell. The oocytes’ long diameter was 4.17 ± 0.21mm and widthdiameter was 3.75 ± 0.19 mm. Egg fertilization rate was 46.7± 24.33%, and larvae weight was 25.48 ± 1.56 mg. CONCLUSIONS:Hematological parameters of juvenile and fingerlingreared beluga showed wide ranges, and there are differences inhematological parameters between reared and wild broodstockbelugas. These findings highlight the importance of hematologicalstudy in wild beluga sturgeon.