Slimy brown gills in post-harvest fish have been observed in Scotland, Ireland and Australia, giving the gills the appearance that the fish have been dead for days rather than hours. Investigations in this problem have shown that the brown gills have a more acidic pH than gills with a normal colouration. A likely explanation for this problem is a build up of blood carbon dioxide levels, the resulting blood acidosis leading to a more rapid post-mortem autolysis of the gills.
Carbon dioxide is excreted from the fish at the gills, across a concentration gradient, thus the higher the environmental CO2, the poorer the excretion of CO2 from the fish. Conditions where CO2 can build up in the environment would include poor water flow through the pre-harvest crowd; or poor off-gassing in a recirculation system on a harvest well boat. This condition can be further exacerbated by concurrent gill disease.
To avoid this happening, always maintain good gill health, ensure there is a good water flow through the pre-harvest crowd; ensure good degassification on the well boat, and keep the pre harvest crowds as low-stress as possible.
