Effect of temperature decrease on hemocyte apoptosis of the white shrimp Litopenaeus vannamei

This study investigated the effect of continuous temperature decrease on hemocyte apoptosis of the white shrimp Litopenaeus vannamei. In the stress group, water temperature decreased from 26 to 17 A degrees C at a rate of 1 A degrees C/h. Shrimp kept at 26 +/- A 0.5 A degrees C were used as control group. Total hemocyte count (THC), reactive oxygen species (ROS) production, cytoplasmic free-Ca2+ (CF-Ca2+) concentration, mitochondrial membrane potential (MMP), apoptotic cell ratio, and caspase-3 activity of L. vannamei hemocytes were determined when water temperature decreased to 23, 20, and 17 A degrees C, respectively. Increased ROS production in hemocytes was observed when water temperature decreased to 20 and 17 A degrees C. Decreased THC and cellular MMP, increased CF-Ca2+ concentration, apoptotic cell ratio, and caspase-3 activity were shown when water temperature decreased to 17 A degrees C. These results indicate that water temperature decrease can induce oxidative stress on shrimp hemocytes and then cause mitochondria and caspase-3 mediated hemocyte apoptosis and THC reduction, when water temperature decreased to an unconformable level.