Exploring the diversity and evolution of fish viromes

Fish have the greatest viral abundance of any group of vertebrates. Their unique and diverse ecologies, in combination with their basal location within the phylogeny of vertebrates makes them excellent hosts in which to study virus evolution. In this thesis, I review the literature on viruses in the marine ecosystem, with a focus on the viruses that infect fish. I then characterise the viromes of nine species of fish sampled from Bass Strait, Australia. As a result, I discovered 15 novel viruses that spanned ten viral families. One of the viruses discovered, flavolineata virus, was of particular interest, as it was the second fish virus to be identified in the Amnoonviridae family. Until recently, the sole member of this family was tilapia lake virus (TiLV), a highly contagious virus that causes mortality rates of up to 90% in infected fish, which has significantly impacted tilapia farming operations globally. The discovery of flavolineata virus sparked further exploration into Amnoonviridae, and through mining published data, my co-researchers and I discovered ten additional viruses in this family. This thesis highlights the abundance of novel viruses that can be found within fish hosts, and expands our understanding of the vertebrate virosphere.