Efficacies of some Beneficial Bacteria on the Colonization and Inhibition of Vibrio harveyi in Black Tiger Shrimp (Penaeus monodon Fabricius) Larvae

Abstract

Eight beneficial bacteria from nature were tested for their colonization and inhibition efficacies on Vibrio harveyi, the causative agent of luminous disease in black tiger shrimp by cross streaking method in vitro. Three types of bacteria showed the best effects against V. harveyi especially in terms of causing its mophological deviation. Nitrosomonas sp. AM-11 showed the fastest colonization activity followed by Bacillus licheniformis AM-04 and B. subtilis AM-01, respectively. However, scanning electron microscope (SEM) revealed that B. subtilis AM-01 caused size and shape of V. harveyi deviated more than others. The virulency of the normal V. harveyi was compared with the V. harveyi colonized by both types of Bacillus in vivo. There were 5 treatments with 3 replications: the first treatment was controlled without V. harveyi ; the second treatment was controlled with APS broth but without V. harveyi ; the third treatment was the normal V. harveyi grown in APS broth ; the fourth treatment was the V. harveyi colonized by B. subtilis AM-01 grown in APS broth ; the fifth treatment was V. harveyi colonized by B. licheniformis AM-04 grown in APS broth. Each replication used 15 larvae aged PL15. Results after 48 hours showed that the mortality of black tiger shrimp from normal V. harveyi was 60% while the mortality of black tiger shrimp from the abnormal V. harveyi colonized by both types of the Bacillus equalled 40%. They were significantly different at 95% confidence from the normal V. harveyi and the control. Therefore, both types of Bacillus could inhibit V. harveyi virulency to some extent. These deviated V. harveyi were still capable of initiating the disease. Nevertheless, in good aquacultural practice, these colonizing bacteria should be used more than once during rearing period.