The following is from Textbook of Fish Health by George Post, 1987, TFH.
Some has been abreviated by myself, others are direct quotes.
Routes of Infection
Most probably is orally (more aimed at hatchery fish I think). Gives
examples of salmon being fed infected fish products.
Injuries or abrasions in the skin (certainly one I have observed). This
can also be helped by external parasites.
Eggs don't appear to transmit the disease. However viviparous fish
(livebearers) _may_ be different.
Other "cold" blooded organisms can carry it including vertebrates and
invertebrates such as snails.
Many strains grow well at 25-32oC. (Ron Bowman was trying to cool his
fish off and could slow or kinda recover the fish I believe. He was still
in the middle of trying last I spoke to him about it 2 years ago).
Strains may invade the skin of humans to produce a disease known as
swimming poll granuloma. Pigeons and mice have found to be susceptible
too. Infection of humans is rare however.
Mycobacteriosis lesions occurring along the gut or in the skin and gills
may be responsiible for release of pathogens into the water. There
probably is little or no release of infective bacteria from other organs
until the fish dies and disintegrates (or gets eaten by the other fish).
Kanamyacin will give limited control when used at 100mg per day of per
fish for 5-10 days. Usually the disease recurs after a short
subsidence. Kanamycin was thought to be successful in the treatment of
platies with 0.01% of the drug in food for four days because no acid fast
bacteria was found after the therapy.
Location and destruction of fishes carry the pathogen is difficult.
Removing faeces (not feces :-) ) from individual fishes and
concentration of the material by digestion, centrifugation and washing,
as discussed above, many demonstrate carriers. These fishes can then be
eliminated from the population.
The chronic nature of mycobacteriosis makes every fish, other
aquatic vertebrates and possibly some aquatic invertebrates carriers of
the disease. Each of the animals in thus involved with the maintenance
and transmission of the disease.
Practical aspects
Three practices to follow to reduce/elimate the disease
1/ Quarantine for at least two months (incubation time of the disease is
at least 6 weeks)
2/ Prevent overcrowding. Use four litres of h2o for each 5cm of fish.
3/ Don't feed contaminated food to the fish. :-)
And from Bruce's last post, keep the organic load on the tank low. When
you water change the tank, also give the filter a rinse in your water
change water if possible as that is where most organics collect.
Tootles
Peter Unmack