When the concentrations of these dissolved gases are above their respective saturation lines, they are in supersaturated state. In contrast, when the concentrations of these gases are below the saturation lines, their dissolution is low-saturated.
The blood and tissues of the fish quickly reach a balance with their surrounding environment. Thus, if the surrounding medium is oversaturated, the blood and tissues of the fish will also be supersaturated. Once in the blood and tissues, the supersaturated gases can leave their solution to form bubbles (embolism), producing the effects of GBD. The main signs of GBD that can cause death, or high levels of stress in fish, are as follows:
• Formation of bubbles in the cardiovascular system, causing obstruction of blood flow.
• Excessive inflation and possible rupture of the swimming bladder in the fry.
• The formation of extracorporeal bubbles in gills of large fish or in the oral cavity of small fish, leading to obstruction of respiratory water flow and death by suffocation.
• Subcutaneous lesions from emphysema on the surfaces of the body, including the lining of the mouth.
Other signs of GBD are ocular lesions, bubbles in the intestinal tract, loss of swimming capacity, altered blood chemistry and reduced growth, all of which may compromise the survival of fish exposed to DGS for prolonged periods.
TASKS
ERH Consult designed a specific system aimed at favoring the partial degassing of water by reducing the pressure (reducing saturation concentration) and creating a thin air – water exchange film (to allow degassing at the new saturation concentration).
To do this, the water was circulated through a reservoir whose purpose is to distribute the water in various landfills and then distribute them in a high surface fill. The reservoir is closed and by means of a compressor it will create a slight vacuum, being able to place the level of gas concentration below the saturation.
The flow to be treated was of 180 l/s and the dimensions of the deposit of 2.0 × 3.1 × 0.8 m.
