TRANSCRIPTOMIC PROFILES OF FLORIDA POMPANO (TRACHINOTUS CAROLINUS) GILL FOLLOWING INFECTION BY THE PARASITE AMYLOODINIUM OCELLATUM

The dinoflagellate Amyloodinium ocellatum is an important pathogenic parasite infecting cultured marine fish worldwide, including cultured Florida pompano (Trachinotus carolinus), which is one of the most desirable and highest priced marine food fish from Florida waters.       A. ocellatum can infect fish skin and gills causing tissue damage, increased respiration rate, reduced appetite and finally devastating mortality, especially in closed systems.

Here, we performed a transcriptomic comparison of gene expression in the gill of healthy and A. ocellatum infected pompano utilizing RNA-sequencing to explore its infectious mechanisms.    

Following sequencing and transcriptome assembly, differential expression (DE) analysis revealed 1041 unique genes with differential expression of greater than 1.5-fold in diseased fish compared to healthy, uninfected fish.   Most striking of the DE genes was the high expression of microbicidal myeloperoxidase (MPO) and eosinophil peroxidase (EPO) that are abundantly expressed in the neutrophil and eosinophil granulocytes respectively and mediate parasite killing and tissue damage by generating reactive oxygen species.  Correspondingly, expression of an array of matrix metallopeptidases (MMPs), often functioning in extracellular matrix degradation were highly stimulated, along with widespread down-regulation of collagen genes.  Several macrophage mannose receptor1 (MMR1) genes were highly induced potentially indicating the recruitment of macrophages to the site of infection.  Expression of IgM increased significantly after infection.  Tissue destruction and inflammation appeared to have downstream impacts on important physiological and metabolic pathways, negatively impacting hemoglobin synthesis, interfering with urea transporters, and establishing hypoxic conditions in the gill tissue.  

Our work provides the first transcriptome sequencing of Florida pompano and provides key insights into the acute pathogenesis of A. ocellatum which can be utilized for disease surveillance and eventual selection for host resistance.