Variation of free amino acid and carbohydrate concentrations in white shrimp, Litopenaeus vannamei: Effects of continuous cold stress

Variation of 19 free amino acids (FAA) in serum and hepatopancreas, glucose in serum and glycogen in hepatopancreas were investigated in white shrimp, Litopenaeus vannamei (IBW 5.0 ± 0.3 g) when water temperature dropped from 28 to 13 °C within 4 days, in order to provide basic data for biochemical changes of the species during cold stress. The results showed that, concentrations of 14 FAA in serum decreased directly with decreasing temperature, with a magnitude of between 12.15% and 400.89%. Concentrations of 5 FAA in hepatopancreas increased directly with decreasing temperature, while that of 8 FAA, remained unchanged or declined at the last stage of the cold stress when water temperature decreased from 18 °C to 13 °C. Exceptionally, concentration of taurine in hepatopancreas continually decreased during the entire procedure. Serum glucose content gradually increased with decreasing temperature, while hepatopancreas glycogen content just sharply declined at the early stage of the cold stress (28 to 23 °C) but slightly changed then (23 to 13 °C). We conclude that quick utilization of glycogen as a temporary energy source occurs in L. vannamei during the early stage of cold stress. Variation of FAA in serum and hepatopancreas reflects a balance of protein degradation and synthesis under the combined stress of cold stress and starvation, and also gives information that FAA may play important roles such as functional substrates or energy utilization for the animal to sustain prolonged and intensified cold stress. So, dietary protein quality and quantity during cold stress should be paid more attention during feed formulation.