What color are the gills? If they are cherry red, then the problem is probably elsewhere. If they are dull pink or white, there could be a gill problem, or the discoloration could be a side-effect of another problem. A few gill parasites, like Ergasilus spp. (fish lice) and Lernaea spp. (anchor worms), can be seen with the naked eye, but others require a microscope and a person familiar with the parasites.
Spring is a time of year when the fish have a supressed immune response, and the warming water gives parasites like Ich, and many other pathogens a "window of opportunity." Therefore, I do not get nervous when I see a few fish die in the spring because there is very little you can do about it and it is normal. I do get nervous if I see dozens of fish dead or dying.
