Effect of hypoxia on the immune response of the abalone Haliotis diversicolor supertexta and its susceptibility to pathogenVibrio parahaemolyticus

Abstract

The abalone Haliotis diversicolor supertexta is the most important aquatic species in many marine farms in China.For the purpose of qualitative observation on the variation of immune defense and natural resistance of animals,the abalones were put into waters with different dissolved oxygen and some immune effectors involved in defense were detected.In this paper the immune response of the abalone and susceptibility to pathogen Vibrio parahaemolyticus under hypoxia stress condition were described.The abalones with an average body weight(14.25±2.21) g could tolerate 120 hours for exposure to a hypoxic condition when dissolved oxygen was reduced from(7.49±0.14) mg/L to(2.53±0.16) mg/L without onset mortality occured at a water temperature(22.1 ±1.3) °C,and a salinity level of 30.72±0.54,and pH 8.20±0.14,but they suffered 91.11%±7.70% cumulative mortality rate which was 80% higher than the control animals due to being challenged with V.parahaemolyticus at a dose of 5.0×105 cells per abalone,and a clearance efficiency in the haemolymph of H.diversicolor supertexta decreased to-(3 340.47% ± 298.57)% inhibition rate.Obviously,the resistance of the abalones to V.parahaemolyticus infection decreaced and the susceptivity inceassed correspondingly under the hypoxic stress above,in which the total haemocytes counts(THC) and percentage of phagocytosis and the amount of superoxide anion(O2-) produced by respiratory burst decreased by 30.62%±4.87%,62.77%±5.79%,and 22.21%±5.89% respectively.That intracellular MPO activity and CAT activity went up from 9.63%±7.59% to 22.90%± 13.73% and 7.68±6.83% to 56.28%±13.96% respectively while dissolved oxygen reduced from(7.49± 0.14) mg/L to(2.53±0.16) mg/L suggests that the intracellular oxidation introduced by hypoxic stress response intensified and there must be much more oxyradicals.The trial abalones of H.diversicolor supertexta possessed a cumulative mortality rate of 37.78±3.85% and a haemolymph inhibition rate of(883.56%±123.22)%,and the maximal downtrends of 12.51%±6.59%,21.90%±15.84%,12.93%±5.74)% in THC and percentage of phagocytosis and the amount of O2-production respectively,and a variation of MPO activity ranges from(10.61%±4.20%) to 7.13%±6.45% and CAT activity from(5.17%±18.08%) to 16.26%±10.85% while not only dissolved oxygen went down from(7.49±0.14) mg/L to(4.51±0.12) mg/L but also infection with V.parahaemolyticus occurred due to the obvious hypoxic stress.