Effects of micro and macroalgal diet supplementations on growth and immunity of greenlip abalone, Haliotis laevigata

Algae contain nutrients and bioactive compounds, which can have effects on the growth and immunity of aquatic organisms. This study examines the effect of macroalgae Ulva lactuca and Spyridia filamentosa, cyanobacteria Arthrospira maxima, and microalgae Dunaliella salina on the growth and immunity of Haliotis laevigata, in comparison to a commercially formulated pellet. Over 12 weeks, U. lactuca or S. filamentosa produced the lowest growth rate, indicating lack of nutrients for abalone growth in a single macroalgae diet. Pellets supplemented with 10% A. maxima or D. salina resulted in increased abalone shell length (13.3 and 30.7%, respectively) and body weight (19.9 and 33.4%) over the pellet control diet. The impact of algal supplementation on hemolymph immunity was mainly represented by a drop in total hemocyte counts (THC) and some diet specific effects on superoxide anion and antibacterial activity against Vibrio anguillarum. No effect of diet was observed on phagocytosis, phenoloxidase, or antiviral activity against herpes simplex virus type 1. It is conceived that the humoral antimicrobial factors in abalone hemolymph are innately biosynthesized rather than dietary derived compounds. Nevertheless, concomitant with strong antiviral activity against HSV-1 in a lipophilic extract of U. lactuca and S. filamentosa, higher antiviral activity was detected in the digestive lipid extract of abalone fed U. lactuca (64.2% at 650 μg ml^-1) or S. filamentosa (69.51%) compared to abalone fed pellets (47.42%) or pellets supplemented with A. maxima (46.3%) or D. salina (46%). This suggests that abalone may also derive some protection against oral pathogens by algal derived bioactive compounds. These results indicate that abalone growth rate could be optimized by A. maxima and D. salina supplementations, whereas U. lactuca and S. filamentosa could be useful supplements for abalone aquaculture, especially in areas with high risk of herpesvirus infection.