Comparative sensitivity of the hepatopancreas and midgut in the white shrimp Litopenaeus vannamei to oxidative stress under cyclic serious/medium hypoxia

Low dissolved oxygen (DO) could cause a stress response in shrimp, the objective of this study was to compare sensitivity of the hepatopancreas and midgut to oxidative stress under low DO. The white shrimp Litopenaeus vannamei were reared under conditions of cyclic serious/medium hypoxia (CSMH, 0.8-3.5 mg/L) versus normoxia (N, 6.4-7.5 mg/L) for a 28-day period. Survival and growth performance of shrimp were evaluated, and hypoxia inducible factors 1a (HIF-1a) expression, antioxidant responses, apoptosis and histology in the hepatopancreas and midgut were investigated. Antioxidant responses tested included the following: manganese superoxide dismutase, glutathione peroxidases, glutathione-S-transferase, metallothionein and heat shock protein70 expression. Results showed enhanced HIF-1a expression and antioxidant responses in the hepatopancreas and midgut during short-term cyclic serious/medium hypoxia (≤7 days), which suggested early adaptive mechanism of shrimp to tolerate low DO and avoid oxidative damage. Meanwhile, HIF-1a expression, apoptosis and histopathological lesions were induced earlier in the hepatopancreas than the midgut. Thus, the hepatopancreas could be more sensitive to low DO and its oxidative stress than the midgut. However, long-term (≥14 days) cyclic serious/medium hypoxia could disrupt cellular antioxidant mechanism with depressed antioxidant responses, and then aggravate apoptosis and histopathological lesions in the hepatopancreas and midgut, particularly the hepatopancreas would lose antioxidant ability earlier than the midgut because of higher sensitivity to oxidative stress. Therefore, we have a few insights that it is vital to protect hepatopancreas for controlling shrimp death and growth inhibition under cyclic serious/medium hypoxia.