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Diseases of Aquatic Organisms

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DAO 50:189-197 (2002)  -  doi:10.3354/dao050189

Effect of nitrite on interaction between the giant freshwater prawn Macrobrachium rosenbergii and its pathogen Lactococcus garvieae

Winton Cheng1, Chun-Hung Liu2, Jiann-Chu Chen3,*

1Department of Aquaculture, and
2Institute of Tropic Agriculture, National Pingtung University of Science and Technology, Pingtung, Taiwan 912, ROC
3Department of Aquaculture, National Taiwan Ocean University, Keelung, Taiwan 202, ROC
*Corresponding author. E-mail:

ABSTRACT: Addition of nitrite-N at 1.5 mg l-1 in tryptic soy broth (TSB) significantly (p < 0.05) decreased the growth rate of the bacterial pathogen Lactococcus garvieae and significantly (p < 0.05) reduced mortality compared to zero nitrite controls when injected into giant freshwater prawns Macrobrachium rosenbergii at 5 x 105 colony-forming units (CFU) per prawn. In other experiments, whereby prawns were injected with TSB-grown L. garvieae (5 x 105 CFU prawn-1) and then held in water containing nitrite-N, mortality at 72 h post-injection was significantly (p < 0.05) higher for prawns held in water containing 1.68 mg l-1 nitrite than at lower concentrations. Prawns exposed to different concentrations of nitrite-N were examined for THC (total hemocyte count), phenoloxidase activity, respiratory burst, phagocytic activity and bacterial clearance efficiency. No significant differences in THC and phenoloxidase activity were observed among treatments. With prawns exposed to nitrite-N for 168 h (7 d) at 1.59 mg l-1, phagocytic activity and clearance efficiency decreased, while at 1.15 mg l-1 or more, respiratory burst increased, generating the superoxide anion at levels considered cytoxic to the host. We conclude that nitrite-N at 1.68 mg l-1 causes depression in the immune response and increased mortality in M. rosenbergii infected with L. garvieae.

KEY WORDS: Macrobrachium rosenbergii · Lactococcus garvieae · Nitrite · Challenge · Virulence · Hemocyte count · Phenoloxidase activity · Superoxide anion

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