Choosing fresh fish (split from Washington DC & Baltimore board)
We are in territory that I actually know a lot about. I managed a fish market in Southampton, NY for almost five years. I know raw fish. I have been to M. Slavin a couple times and was unimpressed overall. Like most places, one needs to judge each individual type of fish, there will always almost be both good and not so good in a case.
If you want whole fish it is easy, just look at the eyes. Clear and bright is what you want. The cloudier they are the older they are. Transluscence and firmness apply here as well (see next paragraph).
For filet, look for transluscent and firm, without any cracking in the filets. Ask to smell it and put your nose right up to it, you want no smell at all. You can even touch it, if it feels greasy, it is old. Filet can easily be "refreshed" with a saltwater or bleach solution, which removes most of the smell and greasiness, but it can still crack and loses some transluscence.
If you are interested in sushi grade tuna, touch and taste. A good fish market should let you taste it. If you touch the tuna (in this case you want it to be greasy from a higher fat content) it should be a little greasy (we can go into grades in more depth later if there is demand) and firm, not separating. Taste it! You can also ask to see a whole filet to check the bloodline, but if you need to do that it probably is not worth eating.
In all the fish that have blood lines, they should be red, bright red. Tuna, swordfish, mahi mahi...I am always amazed at the grey or brown or dark blood lines in fish that people purchase.
Well, that is all I can think of at the moment. I buy quite a lot of fish at Super H Mart in Falls Church. It is almost all whole fish and you choose the fish and select how you want it chopped up or fileted and they do it on the spot at no charge. They also have head on shrimp which is outstanding and denotes that it has never been frozen, but make sure the antennae are long and the head are firmly attached and the guts are not rotting through the shell. Again, there should be very little smell on the shrimp.
"looking at the eyes" is not useful for deepwater fish. Their eyes suffer from being brought up quickly from the depths - much like the bends in humans.
The only way to determine the freshness of ANY fish, other than catching it yourself, is by checking the gills. The darker the gills, the older the fish.
Of course this is totally useless for fillets. You are on your own....
Tuna and swordfish are not beheaded "on the boat." They're sold intact at auction and the condition of the eyes and gills is important to the bidders.
Few consumer fish markets ever buy an entire tuna or swordfish because they are huge.
So you are correct that the condition of an eye is of no use to consumers who will virtually never see a whole swordfish or tuna.
Head off shrimp has been frozen. Leaving the heads and guts in tact gives shrimp a very short shelf life. I have not seen head on frozen shrimp, but I have not looked either. My guess would be to check the length of the antennae, like lobsters, the shorter they are, the older they are.
Maybe you shouldn't be "guessing." Shrimp live only a year or so, max two. Lobsters can live for many years, even 100, so their antennae wear down.
Except for dayboat shrimp, they're "quick chilled" on the boats, which is pretty close to frozen. Most are de-headed and frozen for the general American market since most consumers don't like to buy them with heads on.
Unless you live in the area from Coastal Carolina through the Gulf, you're probably eating "frozen" shrimp whether they have heads on or off, regardless of what the market calls them.
Also press down gently on a whole fish. The flesh should spring back rather than remain indented.
There is no single definitive test for freshness. You need to check as many thing as you can.
Clear eyes. Red gills. No bad smell-while the smell test is one of the better one, it is also the most difficult to describe in writing other than it should not smell like its going bad. I also like to see my fish slimy. Fish with absolutely no slime has been out awhile. Good overall color-nice contrast. See my photo. As a fish deterioates, the colors fade. just like people. Never buy fish where the skin is broken and the internal organs are exposed. Sardines and mackeral are very susceptible to this. Never buy fish where bone and flesh have started to separate. Example-cleaned whole fish-the ribs separate from the meat when you open the body cavity.
I cannot add any more than what has been posted. translucent, good contrast, no smell.
To add to your eating enjoyment, I recomment that you eat only fresh fish and eat it on the day you buy it.