The protective immunity of white shrimp Litopenaeus vannamei that had been immersed in the hot-water extract of Gracilaria tenuistipitata and subjected to combined stresses of Vibrio alginolyticus injection and temperature change

White shrimp Litopenaeus vannamei which had been immersed in seawater (35‰) containing the hot-water extract of Gracilaria tenuistipitata at 0 (control), 400, and 600 mg L−1 for 3 h, were subjected to temperature transfer (28 °C), or combined stresses of Vibrio alginolyticus injection (2.4 × 106 colony-forming unit shrimp−1) and temperature transfer (28 °C) from 24 °C, and the immune parameters including hyaline cells (HCs), granular cells (GCs, including semi-granular cells), total haemocyte count (THC), phenoloxidase (PO) activity, respiratory burst (RB), superoxide dismutase (SOD) activity, and haemolymph protein concentration were examined 6–144 h post-transfer. Shrimp with no exposure to the extract and no temperature transfer served as the background control. Results indicated that these parameters of shrimp subjected to temperature transfer, or subjected to combined stresses significantly decreased to the lowest at 12 h post-transfer. Results indicated that these parameters of shrimp immersed in 600 mg l−1 extract had returned to the background values at 24–144 h post-transfer, whereas these parameters of control shrimp returned to the background values at  ≥144 h post-transfer. It was therefore concluded that the immunity of L. vannamei which had been immersed in seawater containing the hot-water extract of G. tenuistipitata exhibited a protective effect against temperature transfer, and combined stresses of V. alginolyticus injection and temperature transfer as evidenced by the earlier recovery of immune parameters.