Enhancing phagocytic activity of hemocytes and disease resistance in the prawn Penaeus merguiensis by feeding Spirulina platensis

Exposing the prawn Penaeus merguiensis to the bacteria Vibrio harveyi and Escherichia coli for an hour or feeding the prawns with Spirulina (Arthrospira) platensis (0.3% w/w feed) enhanced the phagocytic activity of their hemocytes. Improvement of the phagocytic activity was primarily through the activation of the hemocytes. The activated phagocytic hemocytes had a higher capacity to engulf foreign agents, such as bacteria, and a higher rate of phagocytosis. The phagocytic enhancement effect peaked on the fourth day of feeding with Spirulina. In the in vitro study, the granular cells from prawns took 45–60 min to complete the process of degranulation. Pre-exposure to Salmonella typhimurium and Bacillus subtilis did not result in enhancement of phagocytic activity of hemocytes. Only 10% prawns fed with Spirulina died in the first 14 days when challenged by V. harveyi at a concentration of 1 × 10⁴CFUs mL^–1, while all control prawns (basal feed without Spirulina) died within 14 days.