Andy Turko/University of Guelph

When the water gets too hot, this fish heads to shore

When weather makes the shallow waters in mangrove swamps too hot for comfort, a tiny fish known as the mangrove rivulus (Kryptolebias marmoratus, shown) bails out and briefly moves on shore to avoid neurological damage, researchers say. Previously, scientists had suggested that the fish, besides simply escaping hot water, might be taking advantage of evaporative cooling. Now, using temperature-measuring cameras in first-of-their-kind tests, a team has verified that that cooling process—in which body heat drives evaporation of water on the skin, something akin to human sweating but using water from the environment—is at work. In lab tests, the researchers gradually increased the temperature of water until the fish grounded themselves. Thermal images showed that within 30 seconds, the landlubbers had cooled down to air temperature, the researchers report online today in Biology Letters. Evaporative cooling acts more quickly when relative humidity is low, but the team’s tests show that the phenomenon even works when humidity is an oppressive 95%. Fish that can take advantage of evaporative cooling may have an evolutionary advantage over fully aquatic fish in coming years as coastal waters warm because of climate change, the researchers suggest.