Flow cytometric characterisation of the hemocytes of Roe's abalone Haliotis roei from Western Australia

Abalone are an important commercial species for both wild fisheries and aquaculture in many countries. Since they lack an adaptive immune system, they rely entirely on their innate immune responses both cellular and humoral to defend against pathogens and foreign particles. Understanding the immune system of Roe's abalone is essential for assessing how they cope with environmental, chemical, and disease-related stress. In this study, we examined the morphology and immune functions of hemocytes in Haliotis roei using light microscopy and flow cytometry. We identified three distinct hemocyte types in the hemolymph: granulocytes, hyalinocyte type 1, and hyalinocyte type 2. Flow cytometry revealed clear differences in immune activity between the different cell types. Specifically, we observed differences in lysosomal characteristics such as lysosomal content, as well as mitochondrial, oxidative, and lysosomal activity across all three cell types. Hyalinocyte type 2 consistently showed the highest activity levels. Also, Roe's abalone hemocytes demonstrated a strong immune capacity, with a phagocytosis rate of 81.1% and an average of 18.04 beads engulfed per cell.