Effect of different salinities on the susceptibility of white leg shrimp (Litopenaeus vannamei) to Vibrio parahaemolyticus causing acute hepatopancreatic necrosis disease

Abstract

The purpose of this study is to assess the susceptibility of white leg shrimp (Litopenaeus vannamei) to Vibrio parahaemolyticus, a causative agent of acute hepatopancreatic necrosis disease (AHPND), at different salinities. Experimental shrimp (1-2g/individual) were randomly stocked with the density of 45 individuals/plastic tank (45L in volume) containing 30L of sea water (15ppt) with continuous aeration and temperature was maintained around 28-30 C. Experiment was set up in 12 treatments (in triplicate). Before being challenged with V. parahaemolyticus, salinities in experimental tanks (by group of 6 tanks) were adjusted to 10, 20, 25, 30 and 35 ppt accept 15ppt. Three days after being exposed to different salinities, shrimp from six tanks of different salinities (designated as treatment 7, 8, 9, 10, 11 and 12) were immersion challenged with V. parahaemolyticus. The remaining tanks were kept as un-challenged control groups (designated as treatment 1, 2, 3, 4, 5 and 6). After 10 days post challenge, shrimp in all challenged group had significantly higher mortality rate (ranged from 71± 2.8 % to 89.9 ± 4.9%) (P<0.05) compare to un-challenged control group (ranged from 1.6± 1.3 % to 3.5 ± 1.3%). Shrimps in high salinities (30 and 35 ppt) were more susceptible to V. parahaemolyticus with significant higher cumulative mortality (80.9 ± 4.6% and 89.9 ± 4.9%, respectively) compared to shrimp exposed to 10 ppt (71± 2.8%) (P<0.05). However, there was no significant difference in groups exposed to 15, 20 and 25 ppt. The lethal time (LT50) of challenged shrimp displayed a strong correlation with salinities, the LT50 were significantly lower when shrimp were exposed to higher salinities ((P<0.05).