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Pathogenicity of the Bacterial Isolate Aeromonas Hydrophila to Catfishes, Carps and Perch

M. J. A. Sarkar
Department of Aquaculture, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh

M. M. Rashid
Department of Aquaculture, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh

Abstract/ Executive Summary:

Pathogenicity of a bacterial isolate Aeromonas hydrophila recovered from naturally diseased shing fish was investigated against catfishes (Heteropneustes fossilis and Clarias batrachus), carps (Labeo rohita, Catla catla and Cirrhinus cirrhosus) and perch (Anabas testudineus) of average body weight of 20.4 g for H. fossilis, 25.6 g for C. Batrachus, 35.2 g for L. rohita, 25.7 g for C. catla, 30.5 g for C. cirrhosus and 20.3 g for A. testudineus. Two different doses viz. 6.7 × 106 and 6.7 × 105 CFU/fish were injected intramuscularly. Pathogenicity of A. hydrophila was confirmed at water temperature of 30°C by mortality of 60% to 100% of all the tested fishes within 2-11 days. Injected A. hydrophila was re-isolated from liver, kidney and intestine of all the tested fishes. The highest bacterial loads in catfishes were found to be 5.5 × 108 CFU/g in the liver of H. fossilis and 5.6 × 107 CFU/g in the intestine of C. batrachus. The lowest bacterial loads were found to be 2.2 × 102 CFU/g in the kidney of H. fossilis and 2.4 × 103 CFU/g in the liver of C. batrachus. The highest bacterial loads in carps were found to be 4.9 × 109 CFU/g in the liver of C. catla, 7.7 × 108 CFU/g in the intestine of L. rohita and 5.8 × 108 CFU/g in the intestine of C. cirrhosus. The lowest bacterial loads were found to be 2.7 × 104 CFU/g in the kidney of C. catla, 3.0 ×104 CFU/g in the kidney of L. rohita and 5.6 × 103 CFU/g in the kidney of C. cirrhosus. The highest and lowest bacterial load in perch was found to be 6.4 × 10 CFU/g and 1.6 × 102 CFU/g in the intestine and kidney of A. testudineus respectively. In all the cases of intramuscular injection, external pathology was found. Reddish anal region and fm bases were observed. It was understood that the isolate was a highly virulent pathogen for the challenged fishes.

Keywords: Pathogenicity test, Aeromonas hydrophila, Catfishes, Carps, Perch

Location: Wet laboratory and fish disease laboratory of the Department of Aquaculture, Bangladesh Agricultural University, Mymensingh.

Start Date:

End Date:

Program Area: Pest Management

Commodity: Carp fish

Objectives:

Present work was under taken to know the infectivity of the isolate from the kidney of shing to catfishes (shing and magur), carps (rui, catla and mrigal) and the perch (koi).

Methodology:

The pathogenicity test was conducted at the wet laboratory and fish disease laboratory of the Department of Aquaculture, Bangladesh Agricultural University, Mymensingh. The experimental fishes of average body weight of 20.4 g for shing Heteropneustes fossilis, 25.6 g for magur Clarias batrachus, 35.2 g for rui Labeo rohita, 25.7 g for catla Catla catla, 30.5 g for mrigal Cirrhinus cirrhosus and 20.3 g for koi Anabas testudineus were used for the pathogenicity test of the isolate. Fishes were stocked in cemented cisterns for at least 15 days and then acclimatized in 12 aquaria for 7 days. Every day 50% of total water was changed and the aquaria were covered with synthetic net to prevent the fish from escaping. Intramuscular injection method was used for the challenge test. One ml insulin syringe (sterile and disposable) was used for the injection. A total of 60 fishes (ten fish from :each species) were injected intramuscularly with 0.1 ml of two pre-selected (after Ahmed, 2009) bacterial doses (6.7 × 106 and 6.7 × 105 CFU/fish) just below the dorsal fin after disinfecting with 70% alcohol mixed cotton. Each group was then released in separate aquaria properly labeled to understand the dose and fish species. A negative control group of 10 fish of each species were injected with physiological saline as above. The injected fishes were observed up to 15 days. No feed was given to the experimental fishes and water temperature was recorded twice daily during the experimental period. The average temperature was recorded as 30°C. Each fish was brought to the laboratory immediately after death, dissected out, kidney was touched with a sterilized loop and streaked onto AIM (Aeromonas isolation medium) plates. The plates were incubated at 250C for 48 hours for A. hydrophila colony appearance. Intestine, liver and kidney of each dead fish were dissected out aseptically and placed in sterilized separate plastic petri dishes. After weighing, sample of each of the above organ was homogenized and suspended in sterile physiological saline (1 part of sample: 9 parts of PS) to obtain a stock solution. Two consecutive decimal dilutions, 10-1 and 10-2, from the stock solution were made for each organ. At first the dilutions (stock, 10.1 and 10-2) were used for spreading onto AIM plates to confirm A. hydrophila. Then the dilutions were used for spreading onto -duplicate TSA plates and incubated at 25°C for 48 hours for colony appearance. Appeared colonies were counted by digital colony counter and all the data of bacterial colony counts were recorded for calculating bacterial load in different organs. The bacterial load was calculated by using the following formula after Mamnur Rashid et al. (1994). Bacterial CFU/g of fish organ = No

Source of Information: J. Bangladesh Agril. Univ. 10(1): 157–161, 2012, ISSN 1810-3030

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

From the above discussion it is clear that the pathogen Aeromonas hydrophila is an opportunistic and serious pathogen for catfishes, carps and perch. These pathogenicity test results will be helpful for further study to observe the fate of the pathogen in the organs of these fishes as well as to study the experimental histopathology of these fishes with the bacteria.

Knowledge Management: Journal