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In this study which was carried out in khouzestan province, 1914 Pieces (1160 Pieces silver carp, Hypophthalmychthys molitrix; 498 Pieces common carp, cyprinus carpio; 172 Pieces Grass carp, ctenophryngodon idella and 84 Pieces Big head, Arysthychthys nobilis) from different parts of the province were examined. In three year period, 1378 to 1381, fish samples from four stations were transferred a live to the lab. Water samples also were taken and tested for some of the physicochemical factors. From a total of 1914 fish examined, 1190 showed parasitic infestation and bacterial infections (62.2%). Infestation study, infestation with these parasites have been found: Ichthophthirius, cryptobia, Trichodina, Costia, Hexamita, Dactylogyrus, Gyrodactylus, Lernea, Bothrio cephalus, Diplostomum and Capillaria. Also some species of Aeromonas, staphylococcus, Moraxella, Pectobacterium, Flavobacterium, Citrobacteria, pasteurella, Psedomonas and Alcaligenese were identified in the samples, which normally occur in Water, but in some conditions (High pH, temperature and ammonia) could cause disease and lesions specially in gills. Infestation with dactylogyrus and Gyrodactylus was found in all four kind of fishes with different infestation rate. But the highest infestation rate with dactylogyrus was in silver carp (55.2%) and lowest in common carp (14.6%). The highest infestation rate with gyrodactylus was in grass carp (42.4%) and lowest in common carp (10.6%). Ich, Bothrio cephalus and capillalia were found only in common carp and grass carp. Infestation with adult lernea and copepodid stage of lernea had greater percentage in the gills and derm of grass carp. The data showed infestation with this parasites (especially protozoans and lernea) and bacterial infection had occurred in all seasons especially in C area.

In winter 1994, a mortality up to70% was observed in cultured silver Carp (H. molitrix) in one of the Khouzestan Province fish farms. Bacteriological studies were carried out on the samples obtained from kidney, liver, eroded tails and gills using Cytophaga medium resulted in isolation of filamenus gram negative bacteria. These bacteria were similar to Flavobacterium psychrophilus from point of chemical characteristics. Histological observations showed some necrosis in skin's layers, tissues or livers, kidneys and some sections of gill filaments. Review of present Literature indicate that there is no pervious report on natural occurence of Flavobacrerium psychrophilus infection in silver carp.

In summer 1994, 30 grass carp (Ctenopharyngodon idella) were caught from a pond culture and blood sampling was done, while the fish were alive, for ichthyohaernatologicall examination. The fish and blood were brought to the laboratory, the digestive tract and internal organs of fish were examined for parasitological investigation. Eleven fishes were infected by a tape worm (Bothriocephalus) seriously. Number of parasites in intestine of each fish specimen was between 70 -80 and they cause intestinal obstipation. Amount of haemoglobin, haematocrit value and erythrocyte in infected fishes was lower than healthy fishes.