Microscopic and cytochemical characterisation of haemocytes of the mud crab Scylla serrata (Forskål, 1775) (Decapoda, Portunidae)

Haemocytes of the mud crab Scylla serrata (Forskal, 1775) were characterised based on morphological features using light and electron microscopy, and cytochemistry. The cells were identified as hyaline, semigranular and granular haemocytes. Hyaline cells were the smallest haemocytes among the three types identified, having the highest nucleo-cytoplasmic ratio. The cells showed a number of cytoplasmic organelles and also contained a few small as well as large-sized granules. Semigranular haemocytes possessed moderate numbers of large-sized granules or numerous small-sized granules and comparatively less numbers of organelles. Granular haemocytes were the largest haemocytes with the lowest nucleo-cytoplasmic ratio and contained many large-sized granules. Cytoplasmic organelles were least observed in the granular haemocytes. These three haemocyte morphotypes constituted 60, 21 and 19%, respectively, of the total haemocyte population, while the total haemocyte count was 7.31 × 106 to 7.18 × 107 with a mean of 2.86 × 107 cells ml−1. In cytochemical studies performed to localize carbohydrates, lipids and prophenol oxidase, all the haemocyte types were positive for PAS and toluidine blue, indicating the presence of mucopolysaccharides, whereas semigranular and granular haemocytes were rich in carbohydrates and lipid moieties. Besides, prophenol oxidase was localised within the granules of semigranular and granular haemocytes. Hyaline haemocytes showed an abundance of well differentiated cytoplasmic organelles and granules, and there was a distinct differentiation between semigranular and granular haemocytes in terms of granules and organelles. This is the first report of the characterisation of haemocytes of the mud crab.