Objective The study aimed to investigate the effect of adding microalgae on the growth of juvenile Haliotis discus hannai, and explore the feasibility of Phaeodactylum tricornutum and Chlorella as feed additives for juvenile abalone.

Method 1%, 3% and 5% of P. tricornutum and Chlorella powder were added to the feed (marked as PT1, PT3, PT5, CH1, CH3, CH5, respectively), and compare the growth parameters, total antioxidant capacity (T-AOC), superoxide dismutase (SOD), α-amylase (AMS) and cellulase (CL) activity of juvenile abalone under various treatments, the number of bacteria and vibrio in the visceral sac were compared.

Result The addition of P. tricornutum and Chlorella powder to the feed could significantly increase the shell length, and significantly reduce the mortality of juvenile abalone. The shell length of PT5 was the highest (16.38±2.49 mm), and the mortality of CH1 treatment was the lowest (2.007%±0.67%). The addition of P. tricornutum to the feed significantly increased the body weight and weight gain rate, and decreased the feed coefficient. After 40 days of breeding, the SOD activity of PT5 treatment (12.9±0.75 U/mg) and CH5 treatment (12.99±0.42 U/mg) was significantly higher than that of the control group. The T-AOC activity of PT3 and PT5 (1.15±0.03 U/mg, 1.19±0.06 U/mg) was significantly higher than that of the control group. The AMS activity of PT5 (4.92±0.74 U/dL) was significantly higher than that of the control group, and there was no significant difference in CL activity among different groups. After 40 days of breeding, the number of bacteria and vibrio in the visceral sac of PT5 and CH5 was lower than that of the control group.

Conclusion The effect of adding P. tricornutum on the growth of juvenile abalone was better than that of Chlorella, and the effect of adding 5% P. tricornutum was the most significant.