Are the fish for sushi different from other fish on the market? The answer is yes and no. In a way, any edible fish are suitable for raw consumption if they are fresh enough. But freshness is not the only factor.
When Japanese families in the United States want to eat raw fish at home, they usually buy fish labeled for “raw consumption” at Japanese grocery stores. No one buys fish at regular grocery stores to eat without cooking.
But from my experience, so called “sushi grade” fish is not always fresh. I noticed that one Asian food grocery store, where I used to buy fish for sushi, was selling not so fresh fish for sushi. It was obvious from the foul odor and color. I once returned the fish to the store with a complaint.
It is well known to Japanese families in the United States that farm raised salmon sold at Costco is fresh enough for sushi. Some Japanese strongly disagree that Costco salmon is not good enough, but I often eat it for sushi, and so far I haven’t had any problems.
Many wild fish have parasites called anisakis in their guts due to what they eat in open ocean. As soon as the fish are caught and die, the parasites start to move out from the guts to flesh. Some fish even carry the parasites in the muscles while they are alive.
You don’t die by eating those parasites, but you will experience excruciating pain in your stomach for about 3 days, or until your stomach finally digest the parasites. Some people may need to be hospitalized and operated. Farm raised fish don’t carry anisakis.
Anisakis can be killed by heating or freezing. So that if you want to eat fresh fish you caught on your own for sushi or sashimi, it’s a good idea to freeze it once after cleaning.
I heard that Norwegian salmons are always frozen immediately after they are caught, so that their parasites are dead.
Squid and cattle fish are also known to carry anisakis. The good news about squid and cattle fish is that freezing process not only kill the parasites, but also develops richer flavor.
According to my brother who fishes for his hobby, a fish caught by a net and by a fishing rod tastes differently. A Japanese website that shows how to kill and clean fish after catching explains that when a fish is caught in a net, it struggles violently and injure itself during the process. And the stress of the struggle causes decomposition of amino acid, which is important umami element.
Ideally, blood of the fish be drawn immediately after being caught before being tossed in a cooler (ikejime). There are several different methods of drawing blood from fish. The photo above shows one of the examples, which severs a part of brain stem to kill fish instantaneously. If you just toss your catch in a cooler, the fish will end up with the same fate as it were caught in a net, because it struggles in a small cooler before dying. The point is to kill a fish immediately without stressing it out. A live fish is not equal to fresh fish.
However, catching a fish in the method I described above is labor intensive, and by doing so the fish will be very expensive. If fish can’t be killed immediately one by one using the method above, they are usually frozen to keep freshness. High end sushi restaurants may purchase those instantly slaughtered fish, but that kind of premium fish rarely end up in our mouths.
How to Know the Fish Is Good Enough for Raw Consumption?
You just have to use your all senses and judgement to figure out, because there is no way to get the information about the fish on market. You may know where they are caught, but you can’t know when or how they are caught. The bottom line is that don’t purchase fish if it smells funny. The smell of fish is caused by decomposition process. If the fish is fresh enough, it doesn’t smell.