FISH FRESHNESS
Fish freshness will determine your success in the kitchen, maybe even more than the cooking technique per se (unless you burn it!). However, freshness is also one thing that you cannot influence too much. That's because the difference between fresh and spoiled fish is the difference made by the fishermen and fishmongers.
We mentioned in our other articles that fish meat is very delicate and fragile. It's not a steak. Therefore, it has to be treated with care. When fish is harvested from the ocean, the fishermen can use big nets or simple fishing rods. Of course, the largest catch within a reasonable amount of time is provided by the use of nets. However, it is not the best method for preservation of fish meat quality. If the fish is struggling for too long time, laying in a warmer air, bouncing or being squashed by other fish, along with other inhumane conditions - well, the meat becomes spoiled already there. This is the reality out there. If you can catch fish with a normal fishing rod, or ask someone to do so, the fish will taste much better - provided that you kill it quickly and humanely, and put it on ice right away. There are also the big ships that have their own fish meat preservation facilities on the deck, including quick processing and freezing of fish. Such alternative is also a good way to deliver good fish, although nothing beats the classic fishing rod!
A different way of harvesting fish is used in the fishing farms (aquaculture). First, fish are starved for several days so their guts become clean (less fowl taste influence and less spoiling enzymes), and then they are put to "sleep" with aid of carbon dioxide, and killed by a head smash or bleeding. Fish that has bled is more resistant to several days of storage because lots of its digestive enzymes have left the body.
How can you see if the fish is fresh? There are three basic signs: eyes, glossiness, and belly. The eyes should retain their natural curves and clarity, and don't be opaque and flat. The skin should be shining - that's glossiness - and not dry. The belly should retain it's natural curve and not be swollen (sign of inner spoilage). If you buy fish fillets you cannot really judge the freshness the same way, but you can look at the flesh and see if it's still shiny and not dried out. And the last test of all - smell the fish! Ocean fish should smell like oceanic coast, while freshwater fish should smell kind of grassy. If they smell "fishy" the spoilage has already gone too far. Other tests for fresh fish include looking at the gills (they should be pink-red) and looking at the anus (it should be closed).
Once you've bought the fish, rinse it thoroughly with cold water to wash away all bacteria, dry it, wrap in plastic foil to reduce oxidation, and put it on ice. Of course, the best thing is to prepare it fresh, but if you want to save it for later put it on ice and consume within a few days. Some fish last longer on ice than others; in general, fish that live in warmer waters last longer. You can also freeze the fish for a longer time, but this will destroy some of the texture and flavor due to denaturation of proteins in the freezer that aggregate into lumps when thawed. However, if you still have to freeze the fish, remember to thaw it in refrigerator on in an ice-water bath.
As fish, or any other animal, dies, some moments later its muscles will contract to a static state called rigor mortis. This is caused by depletion of an energy molecule. Some hours or even days later, this tensed muscle state will relax and the flesh starts to separate more and more. What is interesting to notice here is that fish before and during rigor mortis tastes more bity and chewy than the older fish. However, if you don't like to eat a chewy fish make sure it has passed the state of tensed muscles and cook it then, within a day from the end of this stage. This is usually when fish is at its best, when it comes to flavor. Remember also that you can prolong the state of pre-tensation and tensed muscles by putting the fish on ice directly after it's killed (exceptions: sardines and mackerel, should be cooked a.s.a.p.).