Genomic and immunogenic changes of Piscine novirhabdovirus (Viral Hemorrhagic Septicemia Virus) over its evolutionary history in the Laurentian Great Lakes

A unique and highly virulent subgenogroup (-IVb) of Piscine novirhabdovirus, also known as Viral Hemorrhagic Septicemia Virus (VHSV), suddenly appeared in the Laurentian Great Lakes, causing large mortality outbreaks in 2005 and 2006, and affecting >32 freshwater fish species. Periods of apparent dormancy have punctuated smaller and more geographically-restricted outbreaks in 2007, 2008, and 2017. In this study, we conduct the largest whole genome sequencing analysis of VHSV-IVb to date, evaluating its evolutionary changes from 48 isolates in relation to immunogenicity in cell culture. Our investigation compares genomic and genetic variation, selection, and rates of sequence changes in VHSV-IVb, in relation to other VHSV genogroups (VHSV-I, VHSV-II, VHSV-III, and VHSV-IVa) and with other Novirhabdoviruses. Results show that the VHSV-IVb isolates we sequenced contain 253 SNPs (2.3% of the total 11,158 nucleotides) across their entire genomes, with 85 (33.6%) of them being non-synonymous. The most substitutions occurred in the non-coding region (NCDS; 4.3%), followed by the Nv- (3.8%), and M- (2.8%) genes. Proportionally more M-gene substitutions encoded amino acid changes (52.9%), followed by the Nv- (50.0%), G- (48.6%), N- (35.7%) and L- (23.1%) genes. Among VHSV genogroups and subgenogroups, VHSV-IVa from the northeastern Pacific Ocean has shown the fastest substitution rate (2.01x10-3), followed by VHSV-IVb (6.64x10-5) and by the VHSV-I, -II and-III genogroups from Europe (4.09x10-5). A 2016 gizzard shad (Dorosoma cepedianum) from Lake Erie possessed the most divergent VHSV-IVb sequence. The in vitro immunogenicity analysis of that sample displayed reduced virulence (as did the other samples from 2016), in comparison to the original VHSV-IVb isolate (which had been traced back to 2003, as an origin date). The 2016 isolates that we tested induced milder impacts on fish host cell innate antiviral responses, suggesting altered phenotypic effects. In conclusion, our overall findings indicate that VHSV-IVb has undergone continued sequence change and a trend to lower virulence over its evolutionary history (2003 through present-day), which may facilitate its long-term persistence in fish host populations.

The First Record of Bigscale Logperch and Range Expansions of Smallmouth Buffalo, White Crappie, and Gizzard Shad in Arizona

Bigscale Logperch Percina macrolepida is reported and substantiated for the first time in Arizona. A single specimen was collected during a routine survey of Cow Springs Lake on September 26, 2017, preliminarily identified as Percina sp . , preserved, and retained for species identification. We verified the specimen was a Bigscale Logperch through genetic analysis. Review of published literature and the U.S. Geological Survey Nonindigenous Aquatic Species Database suggests that this is the first known occurrence of Bigscale Logperch in Arizona. Further, three additional non-native species were detected during our sampling events on June 21 and September 26, 2017—Smallmouth Buffalo Ictiobus bubalus , White Crappie Pomoxis annularis , and Gizzard Shad Dorosoma cepedianum —representing the first collection of these species in the Little Colorado River basin that we are aware of. We recommend further evaluation of the ecology, distribution, and abundance of these four non-native species to better understand their effect on the native fishes of the watershed and the likelihood of establishment in the watershed and elsewhere in Arizona.