As what has been mentioned--whitish spots that range from just a couple to many, potentially covering the entire fish. There is usually (but not always) scratching and there may be rapid breathing or secondary bacterial infections, which manifest as ulcerations, slime films, etc. If you suspect one or more of your fish have it, posting a pic would be the most helpful in finding out.
ich will look like someone came along while you wasnt looking and sprinkled salt on your fish..lol. there are several things that look kinda similar to it but those form larger white patches not realy the sprinkled salt look. also be sure when treating a tank for ich that you read the directions on whatever it is your treating with because some fish dont like some if the medicine and too much will kill em. one time i overdosed n everyone else got cured but my po' ol' mr.pleco didnt fair as well...it peeled him like a boiled tomato! loaches n plecos are sensitive to itn anything scaleless i think is the way it gos. also add a little icecream salt to the tank, like 1/2 to 1 tsp per 5 galons or so and it helps kill it off, pluss lower the tanks temp a little ich reproduces n spreads faster in warmer water so that helps a little too. hope i covered everything! can ya tell i MIGHT have fought a ick battle or two? LOL!
seems like my first 2 yrs or so i was the ich poster-child! good luck hope this helps!
Beaux
That only works on freshwater fish.
Ich is a parasite not a fungus so make sure if you buy medicine that it is the right one. treat a few days after its gone because even though the fish looks ok the parasite can still be in the tank . It can live without a host (fish) for up to 48 hours and will latch back on to the fish. also most meds require that you take the carbon out of the filter because it will dilute the meds. But the salt trick is better and you should raise the temp a degree or two( depending on how warm you have it already.)
Good luck.
I actually recommend hyposalinity treatment before most medications. Also, marine ich can actually live up to 8 weeks without a host, though 6 weeks is usually the norm.