How to tell what "Fresh" is

I was in a forum today, and got this question, "How do I know what "Fresh" is? And below is what I wrote back. Then, it dawned on me that this would be a great topic for this blog. It is a bit generalized, so if you would like a little more in-depth explanation, just post your question(s) using the comment section.

Yes. Smell is vary hard to mask. If it does not smell like the ocean with a hint of fish, then walk on by. You will know if someone is trying to mask the smell of old fish. It will simply not smell natural. Fish has an amnonia smell to it when it starts to turn. You simply cannot mask that without chemicals. And you will know the difference between chemical and natural smells. The other thing you can do is check the gills if they are present. They should be bright red. And, they should not be slimy at all. The gills are the first thing to turn bad.
The epitome is this: Always ask your fishmonger to let you smell the fish. If it looks bad, it is. For Ahi, it should be dark red without any brown on it at all. Most fishmongers slice their fish into steaks to display in their cases. That is NOT a good practice. If you are lucky enough to have a fishmonger who keeps his loins whole, ask for the center cut if he/she will do it for you. Fish is graded at the processing level. It is graded 1 -2 3 and other. Sashimi/Sushi grade is considered to be a 1 or even better, a 1+. You will pay top dollar for that. You monger better know what he/she is selling. And don't be affraid to ask for proof! All premium grade fish comes with documentation. Even if it is simply on their receiving invoices.
Fresh-Frozen or Fresh? This is a battle that will rage for ages. Some believe that Fresh Frozen preserves the freshness. Some feel that it takes the moisture out of the fish. And there are others who will tell you that they freeze it to cover poor handling. All of which can be true. And again, there are some fishers/processors out there who actually want to keep your business and baby their fish from the minute they hit the deck of the boat. As for Fresh? Who's definition do you want to use? Some believe that Fresh swordfish is what shows up at your fish stand that day, when in reality, it has been covered in ice on a boat for 2 -3 weeks before coming into port. To me, yes, that is still fresh as long as it has been handled right. Each fish has a definite "Fresh" cycle. In other words, each species has it's own expiration date. For some it is just a few days. For others, it could be as long as 3 weeks.
I hope this kinda answered your questions. As you can see, there is never one simple answer when it comes to fish.