What is the majority cause of mortality in cases of gas bubble disease?

Gas bubble disease is primarily caused by the rapid increase in dissolved gases in aquatic environments, which can lead to supersaturation and the formation of gas bubbles in fish tissues. This condition can occur due to excessive pressure changes, such as when fish are transported through varied depths or when water temperature increases, which affects gas solubility.

Water system issues are significant contributors since they can lead to elevated levels of dissolved gases, particularly nitrogen and oxygen, resulting in bubbles forming in fish tissues. These bubbles can obstruct blood vessels and cause distress, which significantly increases mortality rates among affected fish.

While high water temperature can exacerbate the condition by reducing gas solubility, the root cause of gas bubble disease often lies in the water quality management and systemic issues that facilitate the accumulation of excess dissolved gases. Pneumonia and infections from parasites can affect fish health, but they are not the primary reasons for the fatalities associated with gas bubble disease specifically.