Effect of nitrite on immunity of the white shrimp Litopenaeus vannamei at low temperture and low salinity.

White shrimp Litopenaeus vannamei Boone (6-7 cm) were individually exposed during 8 h to 0 (control), 0.5, 1.0, and 10.0 mg/l NO(2)(-)-N at 22 °C and 10 ‰ salinity. Nitrite concentration was measured, and hemolymph and hepatopancreas were sampled at 0, 4 and 8 h. Superoxide dismutase (SOD) activity, catalase (CAT) activity, and malondialdehyde (MDA) in haemolymph and hepatopancreas of L. vannamei Boone, and hemocyanin were examined. The results indicated significant relationships among hemocyanin concentration (Hc), nitrite concentration (nt), and exposure time (t) was as following: Hc = 1.250 + 0.0360 nt + 0.0636t, (R(2) = 0.702, P < 0.01), and Gompertz models with 3-parameters was used to describe well the increase trend of Hc with increase of nitrite concentration at 4, 8 h, respectively (R(2) > 0.99, P ≤ 0.05). MDA level and CAT activity in hemolymph decreased significantly at 8 h, and MDA level and CAT activity in hepatopancreas increased markedly. The SOD activity in hepatopancreas remained almost stably in the range of 0.22-0.24 U/g Hb within 8 h. The results showed there existed a immune difference between in hemolymph and hepatopancreas after white shrimp exposed to ambient nitrite within 8 h, and further experiments should be designed to answer the reason.