A serious disease was recorded in juvenile Pacific abalone in Fujian
Province, China in 2018. Although this disease caused no obvious
external lesions, affected abalone exhibited bleached pedal epithelial
cells and a lack of attachment ability. Bacterial strains were collected
and cultured from the mucus of moribund and healthy abalone. A novel
method was developed for screening abalone pathogens, based on the
important role of mucus in the innate immunity of marine organisms.
Using bacterial isolation, sequence analysis, and experimental
challenges in vitro and in vivo, we identified the bacterial strains
pathogenic to abalone. We verified that abalone mortality rates were
high when exposed to Pseudoalteromonas shioyasakiensis strain SDCH87 at
high temperatures. This opportunistic pathogen had an outstanding growth
ability in mucus, and disrupted first line mucosal immunity in the foot
within three days. The unprecedented sea surface temperatures associated
with the record-breaking 2018 heatwave in south China may have induced
opportunistic pathogenic behavior in P. shioyasakiensis. To our
knowledge, this is the first report to show that P. shioyasakiensis is a
serious opportunistic pathogen of abalone, or possibly mollusks in
general, in the context of a heatwave.