That appears to be fungus more than anything. Fungus is usually a secondary infection or can appear on injuries to your fish.
I can't emphasize this enough, do NOT automatically raise the temp and add salt without knowing what your fish is infected with. I see too many people doing this because it is a common treatment for ich, but there are common infections such as columnaris that will only spread faster and kill quicker with raised heat, and they are generally much more dangerous and lethal than a small ich infection. Combine this with the fact that many natives are much much more stressed from high heat than tropicals (albeit 74 isn't all that high, but I would not raise above about 77) and you may only be hurting your fish.
Fish flashing can be, but is not necessarily an indication of ich. Fish will flash when their body is irritated. This can be caused by any external diseases or parasites that cause irritation, things you add to the water (such as salt) and I have also noticed excess flashing in fish that have internal parasites, relieved after they are fully treated. Internal parasites are quite common in wildcaught fish, as guppy mentioned.
The next thing is to figure out WHY your fish are getting sick. Natives such as bass are usually extremely resistent to parasites such as ich. So automatically you should be looking at your water quality and parameters and determining if this is a factor in your fishes poor health.
Fungal infections can sometimes an indication that you have an excess of solid waste in your tank. Fungus grows on pieces of food and other organic matter that is laying in you tank or sitting in your filters and releases spores that can infect your fish, especially if your fish already have injures or infections. Siphoning your gravel on a consistent basis and doing plenty of water changes will lower the chance of your fish contracting fungal infections. It also seems to be more prevelent at lower temperatures.
You will probably never completely eliminate the chance of fungal infections in your tank because natives such as bass will fight with the other fish and end up with small injuries (magnets for fungus), but you can lower the amount of fungus present in the tank that will infect your fish. Keeping very good water quality will also help your fishes immune system take care of small infections before they become a problem.