عنوان مقاله [English]
Bacterial infectious diseases are one of the important causes of losses in silver carp aquaculture, due to its detritivorous method, that occur due to temperature changes, manipulation and low quality of farmed water. Four fish breeding farms in Sangar area of Rasht, which had silver carp (Hypophthalmichthys molitrix) brood stocks (5.76± 0.99 Kg}, were considered as sampling sites. In order to isolate and identify the bacterial flora of the gastrointestinal tract of silver carp brood stocks fish with apparently healthy appearance, 30 in equal proportions of male and female were selected and samples were prepared individually for culture. The bacterial flora went to culture. After autopsy, the gastrointestinal tract of the fish was removed and preliminary and differential microbial culture was performed from the intestinal contents. The grown samples were purified after replanting and based on the table of chemical tests; their properties were studied and identified as species. There were observed No significant differences in the study of physicochemical variables of sampled farm water and bacterial count of water in sampling sites (p>0.05). After isolation and determination of morphological and biochemical traits, samples of isolated bacteria of 8 genera from the gastrointestinal tract of silver carp brood stocks were identified, the most common of which were Bacillus, Aeromonas and Pseudomonas, although samples opportunistic and general gram-positives such as Micrococcus sp. And Staphylococcus sp. were also observed. Based on the results of this study, there were no significant differences in bacteria count between gram-negative and gram-positive bacteria isolated from the samples (p>0.05). Although many of the bacteria isolated in this study are known to be pathogenic, they are not primary pathogens and are found in and around aquatic bodies and in seawater, estuaries and environments. Fresh water is considered as a part of the natural microflora of the aquatic body and may become pathogenic in conditions of stress and degradation of the aquatic immune system.