Predator avoidance ability of juvenile chinook salmon ( Oncorhynchus tshawytscha ) subjected to sublethal exposures of gas-supersaturated water
To assess the effects of gas bubble trauma (GBT) on the predator avoidance ability of juvenile chinook salmon ( Oncorhynchus tshawytscha ), we created groups of fish that differed in prevalence and severity of gas emboli in their lateral lines, fins, and gills by exposing them to 112% total dissolved gas (TDG) for 13 days, 120% TDG for 8 h, or 130% TDG for 3.5 h. We subjected exposed and unexposed control fish simultaneously to predation by northern squawfish ( Ptychocheilus oregonensis ) in water of normal gas saturation in 6, 18, and 10 tests using prey exposed to 112, 120, and 130% TDG, respectively. Only fish exposed to 130% TDG showed a significant increase in vulnerability to predation. The signs of GBT exhibited by fish sampled just prior to predator exposure were generally more severe in fish exposed to 130% TDG, which had the most extensive occlusion of the lateral line and gill filaments with gas emboli. Fish exposed to 112% TDG had the most severe signs of GBT in the fins. Our results suggest that fish showing GBT signs similar to those of our fish exposed to 130% TDG, regardless of their precise exposure history, may be more vulnerable to predation.