Effects of water pH on susceptibility of whiteleg shrimp (Litopenaeus vannamei) to acute hepatopancreatic necrosis disease Vibrio parahaemolyticus

Abstract

Effect of water pH on susceptibility of whiteleg shrimp Litopenaeus vannamei to acute hepatopancreatic necrosis disease caused by Vibrio parahaemolyticus was carried out in laboratory condition. White leg shrimp (2 - 3 g) were challenged by immersion for 2 h with tryptic soy broth (TSB)-grown Vibrio parahaemolyticus at 10 times lower dose of LD50. The results showed that the cumulative mortality of V. parahaemolyticus-immersed shrimp after 240 h was increased from low to high pH water levels (23.3 ± 5.8% in pH 6.3; 30.0 ± 20.0% in pH 7.3; 86.7 ± 15.3 in pH 9.3, respectively). The cumulative mortality of shrimp that held in pH = 8.3 was the lowest (20.0 ± 0.0%). In another experiment, immune parameters such as total haemocytes count and respiratory burst of Litopenaeus vannamei held at different pH levels were examined at 0, 24, 48, 72 and 96 h. The results indicated that no significant difference of total haemocytes count was observed at different pH water levels (pH 6.3, 7.3, 8.3, 9.3) at 0 - 72 hpc (hour post challenge). At 96 hpc, total haemocytes count at high pH water level (9.3) was increased and significant difference in comparison with the total haemocytes count recorded in low pH water levels (6.3, 7.3, 8.3). Respiratory burst was also not different at different pH water levels at 0 hpc. However, respiratory burst of shrimp that held at low pH water levels (pH 6.3 and 7.3) was rapidly reduced and significant difference in compared with the shrimp that held in high pH water levels (pH 8.3 and 9.3). It was therefore concluded that low and high pH stress decrease the resistance of Litopenaeus vannamei against V. parahaemolyticus and decrease several parameters of the immune response.