Pattamarat Rattanachuay, Duangporn Kantachote and Prasert Suntinanalert

pp. 235 - 243

Abstract

Five isolates of bacteria with high proteolytic activity, isolated from water samples of intensive shrimp ponds in southern Thailand, were selected to test for the ability to control the shrimp pathogen Vibrio harveyi. 70 µl of each culture broth were investigated for their ability to inhibit V. harveyi using an agar well diffusion test but only one isolate W3 gave a reasonable sized inhibition zone of 21.62 mm. This zone was similar to that of oxolinic acid (2 µg) and sulfamethoxazole (25 µg). The W3 isolate was identified as
Pseudomonas sp. Shrimp cultivation in aquaria was conducted to investigate the inhibition of V. harveyi by the isolate W3. The experiment consisted of a treatment of the shrimp culture with an inoculum of the isolate W3 and V. harveyi (biocontrol set), a positive control set (only inoculation of V. harveyi) and a negative control set as without inoculation. No mortality was found in the negative control. Shrimp mortality in the biocontrol set (33%) was lower than that in the positive control set (40%); however, it showed no significant
difference (p>0.05). The average numbers of V. harveyi over 12 days of the biocontrol set were lower than those in the positive control set by about 1 log cycle although the numbers were not significantly different (p>0.05). The shrimp growth rate at day 32 of cultivation was in order of the biocontrol treatment (10.17%)> the negative control treatment (9.44%) > the positive control set (9.28%), but no significant difference (p>0.05) was observed among treatments.

Keywords

• proteolytic bacteria
• Vibrio harveyi
• inhibition
• Pseudomonas sp. W3
• white shrimp cultivation