Identification of Transcripts Relating to Host-parasite Interactions and Feeding-associated Activities Through De Novo Transcriptome Sequencing of Branchiuran Fish Lice, Argulus Foliaceus (Linnaeus, 1758) and Argulus Coregoni Thorell, 1865

Abstract The genus Argulus comprises obligate ectoparasites known as “fish lice” that cause argulosis and significant mortalities in both wild and cultured fish populations. Our previous proteomic analysis confirmed the presence of immunomodulatory products in the secretory / excretory products (SEPs) of Argulus foliaceus (Linnaeus, 1758). In this study, high-throughput sequencing was employed on host-associated stages of A. foliaceus and A. coregoni Thorell, 1865, with comparisons made to a pre-existing transcriptome dataset for A. siamensis. A total of 84,256,934 reads assembled into 66,940 contigs for A. foliaceus, and 10,840,092 reads to give 40,954 contigs for A. coregoni, comprises the largest current genomic data set for the genus Argulus. GO analysis of the top 100 shared genes revealed A. coregoni to be phylogenetically more closely related to A. foliaceus than to A. siamensis. Using OrthoVenn software 6,674 shared gene clusters were identified, and a number of annotated proteins associated with feeding and immunomodulation in other parasites, including 25 trypsin proteins and 8 venom serine proteases amongst others, were discovered. This transcriptomic analysis has contributed to the identification of proteins / genes in Argulus, and the Branchiura more widely, previously characterised as being important immune mediators for other aquatic and terrestrial blood-feeding arthropods.