In India, Labeo rohita is widely cultured and consumed freshwater fish. Aeromonads are etiological agents of major bacterial fish diseases like furunculosis, haemorrhagic septicaemia, skin ulcers, fin/tail rot and dropsy, causing significant economic losses in carp culture. Aeromonas species are widely distributed in aquatic environment which is considered as important vehicle of Aeromonas infections to fish and humans. Some of the Aeromonas spp. causes gastroenteritis, septicaemia, peritonitis, meningitis and eye infections in humans. In the present study Aeromonas species were isolated from diseased freshwater fish Labeo rohita collected from two districts viz., West Godavari and SPSR Nellore of Andhra Pradesh, India. A Total of 12 Aeromonas spp. were isolated and identified by biochemical tests. A. veronii bv. veronii (35%) was dominant when compared to other Aeromonas spp. Further, Antimicrobial resistance and multiple Antimicrobial resistance (MAR) of all Aeromonas spp. were tested against 17 antibiotics being frequently used for human diseases. The Antimicrobial resistance of all the 12 Aeromonas spp. have shown significantly high (p<0.05) resistance (100%) to ampicillin, amoxyclave and oxytetracycline except A. cavernicola when compared to other antibiotics. The MAR index of Aeromonas spp. ranged from 0.18-0.76, which indicates origination of isolated Aeromonas spp. from high risk sources of contamination. A. hydrophila, A. veronii bv. sobria, A. veronii bv. veronii, A. schubertii and A. jandaei isolated in this study were found to be pathogenic to humans also. The results revealed the pathogenic potential of Aeromonas infections in freshwater fish culture and emerging threats to public health.
The microbial composition of rearing water, growth and immune status of Litopenaeus vannamei juveniles in biofloc (T1), substrate-integrated biofloc (T2), substrate (T3) systems and a control with four replicates each were evaluated in a 49-day indoor trail. In each HDPE tank of 70 L capacity filled with 10 g L-1 salinity water, ten shrimp (4.56±0.13 g) were stocked. The C: N ratio of 15:1 was maintained in T1 and T2 using wheat flour as carbon source for production of biofloc. The TAN, NO2 and NO3 were lower (P<0.05) in treatment tanks than that in control. It was also observed that the counts of Bacillus, Lactobacillus, Vibrio and zooplankton were high in T2 than T1, T3 and control. There was higher net weight gain (10.38±0.14 g) and lowest FCR (1.27±0.12) with T2 when compared to T1, T3 and control tanks. Moreover, the survival rate is significantly higher in treatments than control. Significant increase in THC (47.24±4.49 x 106 cells ml-1), serum protein (82.67±0.01 mg/ml), Phenoloxidase (0.73±0.03, OD 490 nm) and Lysozyme activity (56.32±0.03%) was observed in T2 than T1, T3 and control. The result shows that substrate-integrated biofloc system assures higher growth, survival and better immune response in L. vannamei.
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