Cultivation of green algae Platymonas helgolandica in rearing water enhances the growth performance and resistance of Litopenaeus vannamei against Vibrio parahaemolyticus infection

Abstract

Platymonas helgolandica Kylin var. tsingtaoensis, a unicellular free-swimming marine green alga, is widely distributed in certain areas of Asia and frequently used in larvae rearing in marine animal hatchery. To investigate the potential regulatory roles of P. helgolandica in white shrimp (Litopenaeus vannamei) culture, P. helgolandica was seeded in water for rearing white shrimp at three different doses of 1 × 104 (T1), 5 × 104 (T2) and 1 × 105 (T3) cell mL−1 and control without any microalgae for 40 days, and water quality, innate non-specific immune responses (including total hemocyte count (THC), phenoloxidase activity (PO), lysozyme (LSZ), and superoxide dismutase (SOD) activity), shrimp growth performance and shrimp survival rate under Vibrio parahaemolyticus exposure were examined. All the three treatments seeded with P. helgolandica showed a significant reduction of ammonia, nitrite and nitrate. Water pH in each tanks seeded with P. helgolandica tended to increase during the experiment, whereas water pH in the control tanks tended to fluctuate over time. Compared with the control group, final weight, average weight gain and feed conversion ratio (FCR) were significantly greater in T1, T2 andT3. The THCs of the T3 group were significantly higher than that of the control. SOD activities of the shrimp in T2 and T3 groups were significant higher than those of the shrimp in the control. The PO activity of the T3 group was significantly higher than those of the control and the T1 group. On day 10, the survival rate (percent) of L. vannamei under V. parahaemlyticus exposure were 66.67, 81.11 and 91.11% in T1, T2 and T3 respectively, whereas, it was 43.33% in the positive control. These results suggest that seeded P. helgolandica in the rearing water of white shrimp confers positive effects for shrimp aquaculture, considering water quality, growth performance, innate non-specific immune responses and disease resistance. Among the three doses of P. helgolandica, 1 × 105 cell mL−1 had the best effect on shrimp growth performance and resistance against V. parahaemolyticus infection.