Experimental pathogenesis of Aeromonas hydrophila bacteria in shing Heteropneustes fossilis(Bloch)

Pathogenicity of Aeromonas hydrophila bacteria was tested on the stinging catfish Heteropneustes fossilis. Before artificial infection the morphological, biochemical and physiological characters of Aeromonas hydrophila were studied. The infections were done by two different methods, viz., intramuscular (IM) and intraperitoneal (IP) injection. In infection experiment, each group of 10 fish were injected either intramuscularly or intra peritoneally with one dose higher than the LD50 dose (9.6 x 107 CFU/fish). All the fish tested died within 1 to 9 days. Both in cases of intramuscular and intraperitoneal injection, external pathology were found. Haemorrhagic lesions were evident at the site of injection. The posterior end of the body surface was found to develop greyish-white lesion that was extended up to caudal fin. Hyperemic anal region and the fin bases were also observed. Total bacterial loads in liver, kidney and intestine were determined. Aeromonas hydrophila could be isolated from liver, kidney and intestine of the experimentally infected fish. In case of intramuscular injection the highest and the lowest bacterial load was found to be 2.4 x 107 CFU/g of liver and 2.1 x 102 CFU/g of kidney and in case of intraperitoneal injection they were found to be 3.6 x 106 CFU/g of kidney and 1.2 x 104 CFU/g of kidney respectively. It was concluded that A. hydrophila could cause serious disease condition to Heteropneustes fossilis and its pathogenesis in the fish was also very efficient.

Experimental pathogenecity of white spot syndrome virus (WSSV) in Litopenaeus vannamei

The pathogenecity of white spot syndrome virus (WSV) was studied experimentally with challenge exposure of two hundred shrimp with average weight 10 to 12 grams of Litopenaeus vannamei. The shrimp L. vannamei before introducing examined with IQ 2000 detection Kit for WSV. The Fenneropenaeus indicus that showed the clinical sign and PCR positive of white spot disease (WSD) was used the source of WSV. The challenge exposures were accomplished by feeding minced tissue of F. indicus for 24 hours. The result showed L. vannamei after three days revealed the clinical sign of WSV, the PCR examined was positive and all shrimp died after ten days. The shrimp that showed sign of disease were collected for histpathology in Davidson fixator and a part of samples preserved in Ethyl alcohol %75to %90 for PCR. The histopathology showed the effect of virus and cowdly type A inclusion body can see in all tissue except hepatopancreas. The PCR also indicate the virus infected the shrimp Litpeneaus vannamei after 3 days. The SOI and ROI determined the severity of infection and rate of infection in different tissue.