4. TDG Exposure Levels
Depending on the level of supersaturation and the length of exposure, fish may experience very minor affects. For instance air bubbles in our fins may disappear in a day. On the other hand, long or high exposure can cause very severe bubble formation behind our eyes or in our gills, mouths and cardiovascular system. Secondary infections usually occur in these areas, which leads to death.
Scientists know that fish experiencing TDG supersaturation of 115 to 130 percent can experience severe signs of gas bubble disease and high mortality. So to protect fish and other aquatic life, federal, state and tribal agencies have set water quality standards of 110% TDG saturation.
In other words, if 100% saturation represents normal equilibrium with the atmosphere (meaning the same pressure in the water as in the air), the water quality standard says not to exceed "normal" by 10%.
Photo shows gas bubble trauma with a secondary infection.