Background and Aim: Saprolegniasis is a fungal disease that infects freshwater fish. The condition is characterized by a cotton-like appearance in the gills and body. This study aimed to isolate Saprolegnia from common carp, Cyprinus carpio, raised in a floating cage in Wana district, Mosul, Iraq. Materials and Methods: Samples were collected from 15 infected fish and examined microbiologically, molecularly, and histopathologically. Saprolegnia DNA was extracted which was amplified using universal primers give a 540 bp DNA fragment, and gill and muscle tissue were also examined for histopathological changes. Results: Isolated colonies of Saprolegnia were characterized by a circular, white cottony appearance with long hair. Lactophenol staining demonstrated hyphae as branched non-septate, transparent masses. The genomic DNA of isolates was consistent with Saprolegnia spp. The infected tissue samples showed variable pathology in gills. Severe hemorrhage and edema were observed in primary gill filaments with hyperplasia in epithelial cells and infusion in secondary gill filaments. Hyphae of Saprolegnia were seen between necrotic and edematous myofiber with inflammatory cells infiltration. Conclusion: Saprolegnia can cause economic impacts through lethal infection of fish. Clinical signs of Saprolegnia infection were confirmed molecularly and microscopically, and these findings were supported by histopathological lesions in gill and muscle tissues.

The goal of this study was to isolate and identify the causative agents that causes death in Yankee Hatch / Erbil fingerling Cyprinus carpio and to investigate the effect of Cinnamon on the infected fish handled. Both Staphylococcus aureus and Escherichia coli are strongly isolate followed by Aeromonas hydrophila and Klebsiella pneumonia were isolated from liver, kidney and intestine which cause histopathological changes in these organs, characterized by fibrosis in liver, coagulative necrosis in renal tubules in the kidney and sever enteritis. Cinnamomum cassia added to the ration of infected fish at concentration 0.75, 1 and 1.5 % for eight weeks. The histopathological examination reveals that the 1.5% is best the percentage used as food additive for repair and regenerative tissue damage in the liver, kidney and intestine. These study conclude that C. cassia have been used as additive food in fish feed ration at 1.5% and have important role in regenerative tissue damage and keep fish in health status.

The aim of this study is to evaluate the contamination status of Iraqi rivers in the north of the Tigris river (Tikrit city) and the middle region of Euphrates (Babylon Governorate). In this study As, Zn, Fe, Pb, and Cu in the muscle tissue of carp fish were measured. The results show that the concentration of arsenic in the fish muscles in the middle region was 425.05 ppm higher than its concentration of about 192.25 ppm in fish muscle in the Tigris river with statistical significance (P<0.05). Which it causes histopathological changes characterized by Zenker's necrosis in skeletal muscle and infiltration of inflammatory cells with edema additional to edematous dermatitis. Other heavy metals in fish muscle were less than in fish muscles which agreement with the international legislation limits. Also, there were positive correlation ships between Zn and Pb and between Cu and Zn. While negative correlation has been detected between arsenic and both Pb and Zn. This study is concluded that the accumulation of heavy metals causes histological changes in fish muscle provides an opportunity to assess fish health as well as information on possible health hazards coming from their environment.

The fish inhabitant in an aquatic environment so it persists exposure to pathogen and stressor factors so they have a developing immune system similar to that in high vertebrate with some differences points. Head Kidney considered the main and primary hematopoietic organs while spleen, thymus and gut-associated lymphoid tissue represented secondary hematopoietic organs. The immune system divided to the innate immune system doesn’t have a memory of previous responses, non-specific cellular as natural killer cells, dendritic cells, neutrophils, basophils and eosinophils with non-specific component these involve complement, lysosomes and acute-phase protein, if the pathogen persists the specific, memory adaptive immunity would be stimulation which composed of two subunits humeral and natural antibodies act for invading extracellular pathogen and the second subunits which are cytokines and T-lymphocyte act for kill intracellular bacterial, parasitic and viral infection. Both subunits (innate and adaptive) of the immune system act each together in the hosts to prevent microorganism’s infection and reducer the environmental stressors and give fish immune status. It is concluded from this article review that fish, like mammalians, have an advanced immune system that plays a role in fish resistance to pathological factors and maintaining fish health.

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