Isolation and Identification of Silver Carp (Hypophthalmichthys molitrix) brood stock digestive tracts bacterial flora

Abstract

Introduction: 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.
Materials & Methods: 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.
Results: 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).
Conclusion: 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.