In addition to causing stress, which will depress the fish's immune system, such conditions will often encourage increased numbers of opportunistic pathogens. Any treatment plan should also tackle any underlying problems at the same time. Alternatively, for a fuller investigation, they can be removed from the water and lightly anaesthetized for easier handling. Additionally the gills can be examined and skin, gill and fin biopsies can be taken for microscopic examination. Where there are body ulcers, bacterial samples can be taken and sent for investigation.
Surgical examination is also extremely rare and, at present, has a poor success rate.
Blood sampling, which is an important diagnostic tool in veterinary and human medicine, is still poorly developed. Blood sampling techniques are relatively difficult and little research has been carried out as to what would be normal 'baseline' figures for various species and the relevance of variations in blood counts. If detected early enough most simple problems can be easily and speedily resolved. However, there are complications that can arise which can greatly affect both the treatment method and the outcome. If the condition is advanced this can lead to stress and a depressed immune system, possibly leading to secondary infections.