Help! - Possible Fish Tuberculosis outbreak

[wyldchyld01]

chris,

sorry to hear all of the fish have the infection,

sent you a pm

brenton

[Merrilyn]

Chris, have you had any results from the tests back yet? We're all thinking of ya mate.

[Chris McMahon]

Chris, have you had any results from the tests back yet? We're all thinking of ya mate.

Thanks ladyred.

I got the results of the necropsy last Friday.

History
Private aquarium with a community of tropical ornamental fish. Royal whip tail (catfish) culled which had skin red blood spots and bleeding at the vent. Bristle nose corydora (catfish) with circular skin ulcers. Discus appear sick following. Owner concerned about fish TB or mycobacteriosis.

Necropsy
1 bristle nose corydora submitted live for diagnosis. Length 10 cm. 3 large skin ulcers on the head /nose and sides of the pectoral area. Nose ulcer bleeding. Wet mount – gills normal, skin lesion showed moderate amounts of Saprolegnia type fungal hyphae. No obvious internal lesions.

Histology
Liver – some fat deposition. Spleen – mild congsetion. Muscle/skin – inflammation and localised necrosis of dermis and muscle fibres. Kidney – mild calcium deposition in the renal tubule lumens.

Bacteriology
Skin lesion – mixed culture, no significant isolates.

Kidney – no isolates.

Diagnosis
There is no evidence of mycobacteriosis in the fish. The skin lesions are associated with Saprolegnia fungal infection. This is commonly related to organically enriched water/tank environment from either the build up of fish feces and feed wastes or high density of fish and inadequate water exchange or filtration. The calcium deposition in the kidney is a symptom of chronic exposure to elevated levels of carbon dioxide in the water.

Thankfully it isn't fish TB. I was surprised at the "water exchange or filtration" result. I do a weekly sand vacuum on the tank, and do a single 45-50% water chance once per week. I would have thought that as aquariums go, that's more than the average person does.

The high levels of CO2 also surprised me as I don't add any CO2 to the tank, although it is fairly heavily planted. I'd assume then that the high levels of CO2 are from either fish respiration or plant respiration or both.

Management Options

1. Improve the tank environment – regular removal of organic waste build up in the gravel bed. Perform regular water exchanges. Reduce stocking density to control carbon dioxide levels in the water. The more fish in the tank, the higher the production of carbon dioxide gas. Maintain good aeration and avoid excessive feeding.

I've doubled my maintenance on the tank, going from weekly 50% water changes to bi-weekly, with vacuuming at the same time.

2. Salt at 3-5 parts per thousand (ppt) gradually added to the tank as a prolonged immersion to inhibit the spread of Saprolegnia. Use lower dosage of salt for sensitive species such as catfish and discus. Salt is useful to reduce the osmotic stress of fish that have ulcerated wounds. If you are concerned about salt on the discus and catfish – you may separate these fish and treat them at lower doses. Using 3-5 ppt salt is to treat the tank against the fungus. Lower doses may not be effective against the fungus. Note : 3 ppt salt = 3 grams of salt /litre of water. Seawater contains 35 ppt salt. 3% salt = 3 g/100 ml = 30 g/L = 30 ppt = nearly seawater. 3% salt is not the same at 3 ppt salt. Use a hydrometer to accurately measure the salinity of the tank so that the salt level is maintained to inhibit the fungus.

I got preliminary results within 24 hours of dropping the specimen off. At the time it was suggested that I add the salt. I queried the level of salt with a LFS. Normally the maximum level of salt I put in my tanks is 1 teaspoon per 10 litres. 3ppt is 30g per 10 litres, which seems very high to me. For the affected tank (460L) this works out to 1.38kg of salt!! Opinions?

3. The long term control of fungus is in minimising the organic matter in the tank. Treatment with other chemicals such as formaldehyde (formalin), malachite green are usually temporary measures, as the fungus will recur if the hygiene of the tank environment is suboptimal and high stocking densities are maintained.

I talked over the fungus diagnosis with the LFS and they recommended a 1/2 rate does of 3-day white spot cure (active ingredients malachite green and formaldehyde) to control the fungus. I asked the lab what they thought of this as a possible cure.

4. Both formalin and malachite green are potentially toxic to fish and formalin will damage the biofiltration. Formalin should not be used in fish with open wounds. Note : malachite green is carcinogenic (has a risk of causing cancer in people when overexposed to it).

Am I over stocking?

The tank is a 5x2x2. Nominal capacity 550L, actual capacity (taking into account 3D background, sand, height of water vs tank height etc) 460L.

Filtration is 2x Pro Aqua CF-1500 canister running in series (rated 1500L per hour, up to 600L tank - each)

Ammonia 0ppm
Nitrite 0ppm
Nitrate <10ppm

Stock list:
1x adult 12cm discus (Red/White)
3x juvenile 7cm discus (Blue Diamonds)
8x adult 6cm congo tetra
10x adult 8cm rainbows
3x 7cm SAEs
5x 10cm Royal Whiptails
4x 10cm Clown Loaches
10x 3cm platies
6x adult 10cm bristlenoses

I lost on of my 7cm juvenile discus on Saturday. It had turned black (it was a Blue Diamond) in the last few days (it had been dark for a couple of weeks - alternating between looking dark and looking normal) and was fairly thin. Two of remaining Blue Diamonds are darker than normal and looking sick still. I'm worried about losing them too.

Sunday I lost an adult Congo tetra. It appeared to "puff up", sort of like bloat but evenly over the entire body, it swelled maybe 10-15% in size.

So far I've added 1 teaspoon of salt /10L. Dosed 1/2 rate whitespot and have been treating the tank with Pimafix anti-fungal. Apart from 2 dark BD discus, all other fish appear healthy.

I'm still concerned that I might have something other than fungus in the tank. Over the last couple of months I've tried:
-Melafix
-Pimafix
-Tri-sulfa at 1tab/40L and 1tab/20L
-Metronidazole