Water salinity does not affect acute thermal tolerance (CTmax) in zebrafish (Danio rerio)

ABSTRACT Tolerance against acute warming is an essential trait that can determine how organisms cope during heatwaves, yet the mechanisms underlying it remain elusive. Water salinity has previously been shown to modulate thermal tolerance and may therefore provide clues towards these limiting mechanisms. Here we tested whether short (2 hours) and long (10 days) term exposure to different water salinities (0-5 ppt) affected acute thermal tolerance in zebrafish (N=269). We found that water salinity did not affect the thermal tolerance of zebrafish at either time point, indicating that salinity does not affect the mechanism limiting acute thermal tolerance limits in zebrafish. We did, however, observe unexpected behaviour during the CT max test in a subset of fish in the highest salinity treatment after 10 days (3 ppt), indicating some form of salinity-driven disturbance during warming.