The round goby, a small fish, has been making waves in North American waters since the 1990s. It first appeared in the Great Lakes and has since journeyed eastward, reaching the Hudson River Estuary in 2021. Scientists wanted to understand how this fish handles saltwater, especially as it moves into more saline environments. They tested how well round gobies tolerate different salt levels at various temperatures.

The study looked at three temperatures: a comfortable 20°C, a warm 26°C, and a chilly 5°C. Fish were gradually exposed to increasing salt levels, up to 33 parts per thousand. Researchers watched for signs of stress and death. The results were clear: round gobies handled salt best in cold water and worst in warm water. At 30 parts per thousand salt, 87% survived in cold water, but only 7% made it in warm water. This suggests that round gobies might spread into brackish parts of the Hudson River Estuary all year, but they might struggle in very salty areas during warmer months.

Another experiment kept round gobies in saltwater for ten weeks at 20°C. The fish grew less and had lower energy stores at higher salt levels. This could mean that while round gobies can survive in saltwater, it might not be easy for them to thrive and reproduce there.

So, what does this mean for the future? Round gobies might spread into more coastal areas, especially during colder months. This could put other watersheds at risk. However, the fish might face challenges in very salty or warm environments. It's a complex situation that scientists will continue to monitor.

SALINITY TOLERANCE STUDY

Round Gobies: How Temperature and Salt Affect Their Spread

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