Brown blood (Brown Blood Syndrome (NO2 toxi)


Gills brown/red
Gills have a dark brown or dark red colouration.
Nitrite elevated >2ppm
Nitrite levels are 2ppm or above and the lower the pH the more toxic the NO2 will be.
Hanging at surface
Fish stays at water surface all the time.
Seasonal change of temperature
The water has changed in temperature due to normal seasonal variation.
Water temperature low
The water temperature is lower than normal.
Fish gather at water inlets
Fish can be seen in ponds crowding around the water inlets.
Listless and lethargic
Fish moves very lazily in water, much less than normal, lacks interest.
Temperature sudden changes
Temperature has been changed suddenly usually downwards in recent days
Organic load high
Water has a high organic loading and an above normal BOD (Biological Oxygen Demand) reading.
Dark pigment on head
The head of the fish is abnormally dark in colour.
Reluctant to feed
Fish comes to eat but with evident lack of appetite.
Dark body colouration
The colours of the fish are darkened beyond their normal shade.
Gills are partly protruded
Parts of the gills are protruding in abnormal manner.
Gills have excess mucous
Obvious slimy mucous is oozing from the gills of the fish.
Gills swollen
Gills show obvious swelling.
Faded colours
Colour of body has a washed out look.


High Nitrite levels, LOW chloride levels.


Reasonable if remedial action is taken.


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Alleviate conditions contributing to nitrite accumulation.


Dr. Lutz, Greg
Louisiana State University
Louisiana Cooperative extension service
Baton Rouge LA USA


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