Role of Gracilaria verrucosa Extract in the Feed as Immunostimulant of White Shrimp (Litopenaeus vannamei) Infected Vibrio harveyi

| Vibriosis caused by Vibrio harveyi is still a major problem in Pacific white shrimp culture. The development of potential natural compounds to combat bacterial diseases are urgently needed. G. verrucosa, is a marine seaweeds that contains bacteriostatic which is abundance and easily found in all Indonesian marine water. Therefore, G. verrucosa extract could be tested for boosting non-specific immune systems. The research aimed to determine the effect of G. verrucosa extracts in feed on the survival rate, total haemocyte count, and phagocytic activities of white shrimp infected by V. harveyi. A Completely Randomized Design used with five treatments and three replications. The treatments consisted of A (0 g/kg), B (4 g/kg), C (8 g/kg), and D (16 g/kg) of extract/feed respectively. After 14 days fed in various extract concentration, the shrimps were challenge with V. harveyi. The results showed that using G. verrucosa extract the total haemocytes (1.8 X 106 cell/mL), phagocytic activity (65%) and survival rate increased up to 79.2%. This results indicating that G. verrucosa extract stimulated antibody responses. The addition of 16 g/kg G verrucosa extract in feed was the best dosage and able to strengthen the white shrimp’s immune response to V. harveyi infection.