Effects of temperature, pH, salinity and ammonia on the phagocytic activity and clearance efficiency of giant freshwater prawn Macrobrachium rosenbergii to Lactococcus garvieae

Abstract

The giant freshwater prawn Macrobrachium rosenbergii (14–17 g) was exposed to different temperatures (20, 25, 30 and 35 °C), pH values (4.22, 7.27 and 9.31), salinity levels (0‰, 5‰, 10‰ and 15‰) and different concentrations (0.02 (control), 0.55, 1.20 and 3.07 mg l−1) of ammonia-N (ammonia as nitrogen) for 7 days. They were then examined for phagocytic activity and clearance efficiency to the pathogen Lactococcus garvieae. M. rosenbergii at temperatures of 25 and 30 °C, pH 7.27 or salinity 5‰ and 10‰ exhibited increased phagocytic activity and clearance efficiency, whereas M. rosenbergii exposed to ammonia-N at 0.55 mg l−1 or greater exhibited decreased phagocytic activity and clearance efficiency to L. garvieae. It was therefore concluded that at a temperature of 35 °C, salinity 0‰ and 15‰, pH 9.31 or exposure of ammonia-N at 0.55 mg l−1 or greater, the immune system of M. rosenbergii depressed, which in turn resulted in increased mortality from the L. garvieae infection. Prawns at temperatures of 25 and 30 °C, pH 7.27 or salinity at 5‰ however, exhibited the greatest increased resistance to the L. garvieae infection.