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Abstract The barramundi or Asian Sea bass (Lates calcarifer) is of high economic importance for aquaculture worldwide. The present work report a trypanosomiosis of net cage reared barramundi in South China Sea and identified Trypanosoma epinepheli to be the causative agent, which expand the host range of this blood flagellate. This epizootic trypanosomiosis was of distinctly seasonal pattern which occurred from middle-to-late March to middle-to-late May, when water temperature ranged from 21 to 28°C and salinity from 30-33ppt.The infected fish showed typical clinical symptoms of fish trypanosomiosis, including loss of appetite, lethargy, slight emaciation, slightly darken body, swimming lonely and restlessly at the water surface. Mild anemia in gills and remarkable splenomegaly were observed after necropsy. Histopathological investigations showed distinct pathological changes in gill, brain, liver, spleen and kidney, almost consistent with the previous report. This study is the first report of trypanosomiasis in this increasingly important mariculture fish in China. Highlights • This is the first report of trypanosomiasis of Chinese reared barramundi and extends the host range of Trypanosoma epinepheli. [ABSTRACT FROM AUTHOR]

A suspected new enteric Sphaerospora species was believed to be directly associated with the mass mortality of yearling groupers of Epinephelus spp. in South China. The epizootic generally emerged from late September to late April of the following year. The infection prevalence and mortality rate were significantly negatively correlated with fish size. Clinical signs included anorexia, cachexia and extrusion of white pulp-like substance from anus after gentle pressure on the abdomen. Upon necropsy, severe intestinal oedema, thin and transparent intestinal wall, swollen spleen, kidney and gall bladder could be observed. Wet preparation of the infected samples showed large amount of typical disporous plasmodia of the genus Sphaerospora, but no mature spores were observed. Epidemiological investigation showed that this parasite exclusively infected Epinephelus groupers. Histopathologically, this species mainly infected the epithelium of intestine and kidney tubules and caused severe epithelia sloughing and the collapse of intestinal villus. Interestingly, this enteric myxosporidiosis did not cause severe emaciation of infected fish for mass mortality usually emerged within 2-3 days after appearance of clinical signs. The species was most genetically related to Sphaerospora fugu (89% sequence identity) and phylogenetically positioned within marine Sphaerospora lineage. This is the first report of enteric sphaerosporosis of groupers. [ABSTRACT FROM AUTHOR]