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In September 2021, 14 smallmouth bass (SMB; Micropterus dolomieu) with skin lesions were collected from Green Bay waters of Lake Michigan and submitted for diagnostic evaluation. All the skin samples tested positive for largemouth bass virus (LMBV) by conventional PCR. The complete genome of the LMBV (99,328 bp) isolated from a homogenized skin sample was determined using an Illumina MiSeq sequencer. A maximum likelihood (ML) phylogenetic analysis based on the 21 core iridovirus genes supported the LMBV isolated from SMB (LMBV-WVL21117) as a member of the species Santee-Cooper ranavirus. Pairwise nucleotide comparison of the major capsid protein (MCP) gene showed that LMBV-WVL21117 is identical to other LMBV reported from the United States and nearly identical to doctor fish virus and guppy virus 6 (99.2%) from Southeast Asia, as well as LMBV isolates from China and Thailand (99.1%). In addition, ML phylogenetic analysis based on the MCP gene suggests three genotypes of LMBV separated by region: genotype one from the United States, genotype two from Southeast Asia, and genotype three from China and Thailand. Additional research is needed to understand the prevalence and genetic diversity of LMBV strains circulating in wild and managed fish populations from different regions. [ABSTRACT FROM AUTHOR]

A multi-laboratory broth microdilution method trial was performed to standardize the specialized test conditions required for the fish pathogens Flavobacterium columnare and F. psychrophilum. Nine laboratories tested the quality control (QC) strains Escherichia coli ATCC 25922 and Aeromonas salmonicida subsp. salmonicida ATCC 33658 against 10 antimicrobials (ampicillin, enrofloxacin, erythromycin, florfenicol, flumequine, gentamicin, ormetoprim/sulfadimethoxine, oxolinic acid, oxytetracycline, and trimethoprim/sulfamethoxazole) in diluted (4 g l-1) cation-adjusted Mueller-Hinton broth incubated at 28 and 18°C for 44-48 and 92-96 h, respectively. QC ranges were set for 9 of the 10 antimicrobials. Most of the minimal inhibitory concentration (MIC) distributions (16 of 18, 9 drugs at both temperatures) for A. salmonicida ATCC 33658 were centered on a single median MIC ± 1 two-fold drug dilution resulting in a QC range that spanned 3 dilutions. More of the E. coli ATCC 25922 MIC distributions (7 of 16) were centered between 2 MIC dilutions requiring a QC range that spanned 4 dilutions. A QC range could not be determined for E. coli ATCC 25922 against 2 antimicrobials at the low temperature. These data and their associated QC ranges have been approved by the Clinical and Laboratory Standards Institute (CLSI), and will be included in the next edition of the CLSI M49-A Guideline. This method represents the first standardized reference method for testing fish pathogenic Flavobacterium spp.