I thought I would offer a discussion about what makes good quality. Spoiler alert, it does not entirely have to do with when it came in to our shop. By and large it boils down to a few key things:
Time out of water
How it was handled after it was caught
Nature of the fish
Time out of water
As I've mentioned before, there are "day boats" that go out fishing for one day and "trip boats" that can go out for 2 - 3 days up to a month (in the case of sword and tuna). Ideally, we'd buy all our fish from day boats. However, this is not possible for every species (particularly in the winter) because some species swim farther offshore and boats need to go farther to get them, which requires a multi-day trip. If this is the case, we buy from suppliers who buy the "top of the catch", meaning the fish that was caught on the final day of the fishing trip.
How it was handled
This may be the most consequential corollary to fish quality. If a fish is killed, bled and iced immediately after catch, that fish (even after being filleted) will hold its quality far, far longer than a fish that was not handled this way. Even just icing the fish immediately after catch goes a long way to preserve quality. Again, we rely on our suppliers to buy from boats that treat the fish well.
Note that killing and bleeding fish immediately after catch is a common Japanese fishing technique called No-Jime. Unfortunately, this practice is not common in the United States. I am currently a sponsor of a federally funded grant project to help train local fisherman on this technique and promote its widespread adoption. Ultimately, this could dramatically improve the shelf life of fresh fish. I'll keep you posted.
Related to fish handling is catch method. Rod and reel fishing tends to yield the best quality, where the fish will be caught alive and can be killed and iced quickly. Other methods, such as gillnetting, can be less quality supportive. With gillnetting, fish can struggle in the net and ultimately die in the net in the water. This can mean significant lactic acid leaching into the fish flesh and then a dead fish hanging in warmish water, which is also not good. We try to get fish caught with more quality friendly methods, which include (but not limited to): rod and reel, long line and dragged (big net that scoops up the fish)).
Nature of the Fish
For some fish, the quality can just be the luck of the draw attributable to natural factors. For fish we offer, this is most relevant to Bigeye Tuna and Halibut. Bigeye (and Yellowfin) Tuna can have wide color variation (consistent, strong red color is the most desireable). Certainly, handling can contribute to this, (poor handling will cause the fish quality to deteriorate quickly and typically the color will deteriorate with it), but color can also be determined by diet or other factors that we don't entirely understand. This means that two fish might have been handled the exact same way (and handled properly) and one has a deep, sushi red color and the other has a lighter color (side note - in this example, that lighter color tuna would be perfectly good for sushi, it just wouldn't have the same market desirability or be considered of the same quality level/grade and the deep red fish).
Halibut can get "chalky" (opaque vs translucent meat), which is thought to sometimes be caused by lactic acid leaching into the flesh during catch (and some improper handling), but it's also widely accepted that this could be attributable to water temperatures or just the nature of the fish.
The big takeaway here is that a lot that happens before a fish gets to the shop that contributes to fish quality. Given this, the best question to ask us is not, "what came in today" or "what's newest", but rather, "what are we most excited about".
