Here are some of the things I came across in my research of fungal/Yeast(Candida albicans) infections. Of course, not every bird will show every symptom and these symptoms are definately symptoms of other illnesses as well, including canker.
o Inappetance.
o Weakness.
o Silent gasping.
o Rapid breathing.
o Thirst/increased drinking.
o Drowsiness.
o Nervous signs (rare).
o Wasting.
symptoms are gasping, coughing, stretching of the neck, shaking head, sleepiness, loss of appetite, rapid loss of weight and sometimes convulsions and death.
Base of feathers on back of neck become raised and feathers come out easily.
Alot of these symptoms will show up when it is too late. Symptoms will be magnified in times of stress and may be hidden when not stressed. In times of heavy stress, fluid or mucus can be found coating entire mouth, even dripping out.
Respiratory symptoms may show up in later stages and when treated with respiratory meds, will seem to improve condition immediately but is short lived and will quickly worsen.
This is all due to a lowered immune system and secondary infections are likely. You may be dealing with one or more illnesses at one time.
I have gone over many websites regarding this because I am dealing with it also i believe. I have been having great luck with my treatments so far. My birds appears to be getting much stronger. Some of the sites I pulled info from include Mississippi state university extension system, the poultry site, University of Florida and many many more. I just read and read and read until I couldnt read any more.