Here are some links that contain some information of flukes:
This article states that symptoms may be white patches on skin, scratching, rapid breathing, or worms on skin. If the gills re affected the fish may suffocate. Treatment is with anti fluke meds.
This site shows how to do a skin and gill scrape to examine under the microscope.
This article lists gasping near surface, rubbing, opaque mucos on the gills, filaments protrude from the gills, rapid breathing, or one gill closed, all as possible signs of flukes. Treatment is salt 4 oz/ 10 gal , for 3 wks, or formalin at 3 to 6 drops /gal for 8 hrs then 50% wc, or formalin/malachite green (most effective in authors est.), or formalin bath at 15 drops/gal for 30 min,
This article has an interesting picture of how flukes attach to the fish. It states outbreaks are caused by stress to the fish including poor water conditions and poor parameters. Breathing abnormalities and lethargy are possible signs of infestation. Fins can be clamped. Gills can protrude and become pale and slime covered.Treatment is with formalin, acriflavine, methylene blue, chloramines, and a couple others.
This article talks about the caterpillar like attachment of flukes to fish. Salt baths, malachite and formalin are sometimes used to treat. Masoten is used for an all out war on flukes. Chloramine-T is also used. The gill fluke is harder to eradicate than the skin fluke.
In this article Jim Quarles recommends using a microscope for identification, and looking at gill color. Formalin, malachite, copper, and prazi are talked about as treatment options.