Bacterial Gill Disease

Bacterial Gill Disease (BGD)

Fish gills, unlike the rest of the body, can't be readily seen and often by the time it has become obvious that the fish is ill, it has become too late. The damage is advanced and, in most cases, untreatable. Therefore vigilance and early diagnosis and treatment is vital.
One such disease that occurs in fish is BGD. It is caused by a number of different bacteria that infect the gills. The disease manifests itself by the presence of large numbers of filamentous bacteria on the gills which cause clubbing and fusing of the gill filaments themselves. The ability of the gills to supply oxygen to the blood is greatly reduced and can result in the loss of the fish if left untreated.
The presence of BGD is linked to a decline in the conditions in which the fish are kept, in combination with overcrowding, it is contagious and can be brought on by gill flukes, although this is not always the case.


What to look for:-

Fish that are infected with BGD may show a need for more dissolved oxygen in the water and may be seen gasping for air at the surface, or frequent areas of the pond where more oxygen is available, ie; a waterfall, weir or fountain, air stones and diffusers, anywhere where water is falling into the pond and creating extra oxygen bubbles. The early signs are fish respiring heavily. You can judge this by watching the operculum (gill plate) movements and comparing them to other fish. They may be seen laying on the bottom for long periods , have a general lethargy, and may not be eating.
At a more advanced stage you may notice that the fish can't fully close the operculum because of gill swelling.
At a really advanced stage - and usually too late for treatment - the fish will lay on the bottom with its pectoral and dorsal fins clamped to its body - literally waiting to die!
However, increased ammonia or other water problems, the possibility of gill flukes, or simply a lack of dissolved oxygen can cause fish to exhibit the same behaviours so these need to be over-ruled before assuming that is it BGD as these are more common.


Diagnosis :-

Looking under the gill plate (operculum) will provide more information. If the gills look scared or discoloured, torn or uneven, are clumped or fused, it may indicate BGD. The gills may also have the appearance of raw, shredded meat instead of their usual healthy look and colour.
High levels of ammonia can also cause this clumped and fused look, which is irreversable, but the damage from BGD will be much worse. Healthy gills have even edges and lie in semi-circles, they are deep red in colour with no patches of discolouration. Feathered edges and white streaks indicate unhealthy gills and any grey indicates areas of dead tissue.
White on the gill edges points to ammonia, nitrite or PH crash burn and should not be confused with the damage caused by BGD.

Treatment :-
 
Obviously treatment will depend on the cause and if gill flukes are suspected they need to be identified and erradicated. Looking at a mucus scraping under a microscope would be the ideal, but if you do not have the equipment or experience for this assume that flukes are present and treat accordingly with a preparatory treatment such as Fluke Tabs, Anti-Fluke or Prazi Pond.
After this you would then treat for BGD with a specially formulated medication, such as BGDX by Argent Labs. If using this you will need to by-pass biological filters while treating or nitrifying bacteria will be killed.

As an extra precaution triple antibiotic food should be fed during treatment.


Aftercare :-

Fish that have had BGD and survived will have permanent scarring on their gills and will therefore need the provision of extra oxygen in the pond as their gills will never regain full working capacity. An aeration pump and air diffuser will help to maintain higher levels of oxygen and thus give the survivors the more oxygen rich environment that they will need.

Prevention :-

As all fish keepers know the key words are water quality, water quality and water quality. This is probably the best thing to prevent BGD. Make sure the filter you are using is sufficient for the size of your pond and the quantity of fish, and if you can afford it  - go bigger! You can never have too much biological filtration.

Do not make it any easier for bad bacteria to breed, ie; keep the pond well aerated and the water cirulating, do not use large numbers of rocks and pebbles on the pond bottom as these can harbour organic material where bacteria can reproduce.