Tissue Distribution and Abundance of the Parasitic Dinoflagellate in Naturally Infected .

The parasitic dinoflagellate is an infectious pathogen that causes severe enzootic in numerous economically important marine crustaceans worldwide. Previous research has focused on investigating the identification and life stages of parasites, while the parasite abundance and tissue proliferation process of in naturally infected crustacean hosts need to be further studied. In the present study, the tissue tropisms and intensity of were investigated in the naturally infected Chinese swimming crabs by both the qualitative (hemolymph assay, histology) and quantitative analysis (cell count, quantitative PCR). The results showed that in with infection level I (4 ± 2 parasites in 200× microscopic field), filamentous trophonts were observed in the hemolymph and stomach tissues, with the average parasite number and ITS 1 copy number of quantitatively detected in hemolymph (1.0 × 10 parasites/mL) and stomach tissues (1.7 × 10 cells/g), respectively. trophonts were observed in the hemolymph (4.3 × 10 parasites/mL) and exhibited broad distribution in multiple tissues with its highest abundance of in pereiopod muscles (1.1 × 10 cells/g) followed by that in stomach (4.8 × 10 cells/g) in with infection level II (80 ± 10 parasites in 200× microscopic field). In with infection level III (200 ± 35 parasites in 200× microscopic field), a high abundance of sporoblasts was found in the hemolymph (3.1 × 10 parasites/mL) and all of the other examined tissues, with its highest abundance detected in pereiopod muscles (3.5 × 10 cells/g). In addition, the number of host's hemocytes was significantly decreased during the infection. This study provides a comprehensive quantitative characterization of the tissue distribution and abundance of in its natural crab host which will contribute to better understanding of the crustacean host- interactions.