Editing Fish migration (section)

== Myxovirus genes ==
Because [[Salmonidae|salmonids]] live an anadromous lifestyle, they encounter a larger range of [[viruses]] from both freshwater and marine ecosystems. Myxovirus resistance (Mx) proteins are part of a [[GTPase|GTP-ase]] family that aid in viral immunity, and previously, rainbow trout (''[[Rainbow trout|Oncorhynchus mykiss]]'') had been shown to possess three different Mx genes to aid in viral defence in both environments. The number of Mx genes can differ among species of fish, with numbers ranging from 1 to 9 and some outliers like [[Gadiformes]] that have totally lost their Mx genes. A study was performed by Wang et al. (2019)<ref>{{Cite journal|last=Wang|first=T.|date=2019|title=Lineage/species-specific expansion of the Mx gene family in teleosts: Differential expression and modulation of nine Mx genes in rainbow trout Oncorhynchus mykiss|journal=Fish and Shellfish Immunology|volume=90|pages=413–430|doi=10.1016/j.fsi.2019.04.303|pmid=31063803|hdl=2164/14229|s2cid=147706565 |hdl-access=free}}</ref> to identify more potential Mx genes that resided in rainbow trout. An additional six Mx genes were identified in that study, now named Mx4-9. They also concluded that the trout Mx genes were "differentially expressed constitutively in tissues" and that this expression is increased during development. The Mx gene family is expressed at high levels in the blood and intestine during development, suggesting they are a key to immune defense for the growing fish. The idea that these genes play an important role in development against viruses suggests they are critical in the trout's success in an anadromous lifestyle.