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Isolation and Biochemical Characterization of Bacterial Pathogen in Commercially Important Shrimp and Fish Collected from Ghers in Satkhira District, Bangladesh

Banu Ghausiatur Reza*
Fisheries and Marine Resource Technology Discipline,, Khulna University, Khulna-9208, Bangladesh

Reza Md. Mohashin
Fisheries and Marine Resource Technology Discipline,, Khulna University, Khulna-9208, Bangladesh

Abstract/ Executive Summary:

Investigations were carried out for isolation, enumeration and characterization of bacterial pathogens from shrimp Penaeus monodon and vetki Lates calcarifer from different ghers at Asasuni thana of Satkhira district. Shrimp and vetki were randomly sampled with a cast net from each gher individually during the period of September to December, 2005. After sampling, the live specimens of 20 shrimp and 12 fish were brought to the laboratory and immediately dissected. Muscle, hepatopancreas and gill were removed aseptically, weighed and homogenized with 0.85% NaCl solution. The homogenate was diluted using consecutive decimal dilution and inoculated on standard agar plates for enumeration of total bacterial load. A total load of 106-7 CFU g-1, 105-6 CFU g-1 and 107-10 CFU/g-1 were found in hepatopancreas, muscle and gill of shrimp and 105-6 CFU g-1, 106-9 CFU g1and 107-10 CFU ml-1 in fish muscle, gill and slime, respectively. The total bacterial load in water of the ghers was estimated to be 107-10 CFU ml-1. A total of 32 and 20 representative isolates were selected from shrimp and fish respectively to identify them up to the genus through morphological, physiological and biochemical properties. Four genera namely, Vibrio, Micrococcus, Aeromonas and Pseudomonas were identified from the samples. Vibrio (56%) was predominantly isolated followed by Micrococcus (19%), Aeromonas (16%) and Pseudomonas (9%) in P. monodon whereas Pseudomonas (45%) dominated in L. calcarifer followed by Aeromonas (30%), Micrococcus (15%) and Vibrio (10%). High bacterial load in shrimp, fish and water of the ghers, it can be assumed that shrimp culture of Satkhira district is susceptible to bacterial contamination specially vibrio which is one of the devastating pathogens causing vibriosis in our country.

Keywords: Bacterial content, Opportunistic pathogen, Vibrio, Penaeus monodon, Lates calcarifer

Location: Ghers in Satkhira District, Bangladesh

Start Date:

End Date:

Program Area: Pest Management

Commodity: Shrimp, Fish, Bacteria

Objectives:

These bacteria infect a wide range fish from freshwater to seawater. Various information regarding good culture practice, feed, management techniques are available (Karim, 1993; Hossain, 1994). However, information regarding disease, pathogen of fish/shrimp is limited in our country especially covering Khulna, Satkhira region. So this study was attempted to assess common microbial pathogen especially bacterial flora available on cultured shrimp and fish from shrimp ghers. The objectives of the present investigations were to isolate, enumerate and characterize some bacterial pathogens from commercially important shrimp Penaeus monodon and vetki fish Lates calcarifer.

Methodology:

Selection of the study area: The study area had been selected at the southern part of Bangladesh which is well known shrimp resort in Bangladesh. Samples were collected from three different ghers locally named as Barainer, Koikhali and Uttar beel at Asasuni thana in Satkhira district. Samples and sampling: Juvenile live shrimp P. monodon and fish L. calcarifer weighing of 16 g and 152 g respectively were randomly collected by netting from the selected ghers during the period from September to December, 2005. After harvesting the samples were then immediately taken to the laboratory using oxygenated polythene bags containing water from the same gher. In each sampling, five shrimp and three fish were examined from each gher. For the isolation of suspected bacterial pathogen, the organ samples of gill, muscle and hepatopancreas from P. monodon and gill, muscle and slime from L. calcarifer were removed aseptically, weighed and homogenized properly with 0.85% NaCl solution by tissue homogenizer. The homogenate were then diluted using consecutive decimal dilution and inoculated on to the medium.

Enumeration of total bacterial load: Bacterial content of the samples were determined by standard plate count method. An aliquot of 100 µl of each decimal dilution was spread separately on duplicate plates having the nutrient agar medium and incubated for 24-48 h. When the colonies became clearly visible within the range of 30-300, then total bacterial load were counted and expressed in CFU g-1 or ml-1 of sample. Characterization and identification of the isolates: In order to identify the bacteria, some representative isolates were selected from P. monodon and L. calcarifer. Morphological and biochemical characteristics of each isolate were studied according to the methods described in Cowan and Steel’s Manual for the Identification of Medical bacteria edited by Barrow and Fetham (1993). Isolates were identified up to the genus level using the taxonomic key developed by Tonguthai et al. (1999). The mean percentage of identified bacterial genera isolated from the gill, muscle, slime and hapatopancreas of the shrimp and fish was also calculated.

Source of Information: Khulna University Studies, Special Issue (1st Research Cell Conference): 99-103, 2006

Article Link (Online Journal):

Funding Source:

1.

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Considering high bacterial load on various organs of shrimp, fish and the water of ghers, and the genus detected in our investigation, it can be concluded that shrimp culture of Satkhira district are susceptible to bacterial contamination, specially Vibrio, which is one of the devastating pathogen causing vibriosis in shrimp in our country. Though it was not possible in our study to pinpoint which genus caused various clinical diseases faced by the farmer, however this baseline data could serve as a useful indicator to determine the potential hazards to P. monodon and L. calcarifer in gher poly-culture system which has a great economic consequence to our country.

Knowledge Management: Journal