Most people buy tinned fish twice. Once when they want tuna salad, and once when they've seen a tin of something beautiful on Instagram. The two tins cost different amounts, live in different aisles, and are designed for two completely different jobs. Almost nothing written about tinned fish explains this clearly, so here it is.

The supermarket-aisle tin is simply an ingredient fish tin that's purposefully made to disappear into something. Chunk light tuna in water, the 5-ounce can with the pop-top, is the canonical example. It is designed to be mixed with mayonnaise, baked into a casserole, melted onto toast with cheese, or folded into a pasta. The fish is broken into flakes because flakes mix well. It is packed in water or cheaper oil because that's not meant to be eaten by itself. It is designed to be a cheap product because it needs to be.

This tin is not a lesser product by any means. It is the right product for the job to be performed.

The flakes bind with the mayonnaise in a way the loin won't. The supermarket-aisle tin is the right tool when the fish is a building block.

What a supermarket-aisle tin looks like: a steel or aluminum can, often with a pop-top lid. Flaked or chunk fish. Packed in water, soy oil, sunflower oil, or "vegetable broth," a flavor enhancer StarKist's own FAQ describes as a blend of two or more of beans, cabbage, carrots, celery, garlic, onions, parsley, peas, potatoes, bell peppers, spinach, or tomatoes. A price in the low single digits. Brand names like StarKist, Bumble Bee, Chicken of the Sea, Great Value. The label usually says "tuna" without specifying a species, which by Spanish labeling convention almost always means skipjack, the cheapest category.

The fish-first tin is a complete, ready-to-eat finished dish. Opening one of these is usually the last step, not the first. A tin of Ortiz bonito del norte packed in extra virgin olive oil costs in the low teens for a four-ounce tin. You peel back the lid, tear off a piece of bread, and eat. Nothing is added, nothing is cooked.

The usage is much simpler than most guides make it sound. Tinned mackerel in olive oil goes directly onto a thick slice of sourdough, with a crack of black pepper and maybe a squeeze of lemon if one is nearby. Sardines in tomato sauce go onto a piece of crusty bread that can soak up the sauce without falling apart. A tin of mussels in escabeche gets eaten straight, with bread for dragging through the vinegar and oil at the bottom. The oil itself is the second half of the dish. You drink coffee with it, or a cold beer, or a glass of white wine, or nothing at all.

In Galicia, the bocata de sardinas is a sandwich made by splitting a crusty roll, pressing in sardines from the tin, spooning the oil from the tin over the bread, and sometimes adding a smear of tomato or a few slices of raw onion. It is a lunch, not a presentation. In Portugal, tinned sardines on toast with butter is a standard afternoon snack. In the Basque Country, bonito is flaked onto bread with a pickled guindilla pepper and eaten standing up at a bar. None of this requires pre-preparation or sides or a board. It requires opening a tin and having something to put the fish on.

In Spain and Portugal, conservas, tinned, jarred, or preserved seafood, are enjoyed as their own course, with a cold beer or some wine, often at the center of a meal. This tradition is what the American tinned fish moment is currently importing. Minerva sardines in spiced olive oil with piri-piri are a cheap example of a fish-first tin, typically a few dollars for a small can. Ortiz ventresca, the fatty belly of the albacore, is an expensive one, often well above ten dollars for a four-ounce tin. Both are designed to be eaten as-is.

What a fish-first tin looks like: a steel can or glass jar, often pry-open rather than pop-top. Whole fillets, loin pieces, or whole small fish, not flakes. Often grilled, smoked, and/or packed in things like olive oil, escabeche, tomato sauce, piri-piri, or butter. Prices range widely, from the mid single digits up into the tens. A species named specifically on the label: Sardina pilchardus, Thunnus alalunga, Scomber scombrus. Usually from a country of origin outside of the United States, and with a pack date rather than just a best-by date.

You can easily tell which world a tin belongs to before you pick it up. The signals are consistent.

The species name. A supermarket-aisle tin says "tuna" or "chunk light tuna." A fish-first tin says "Bonito del Norte (Thunnus alalunga)" or "yellowfin tuna (Thunnus albacares)." The Spanish designation "Bonito del Norte" is legally restricted to Thunnus alalunga from the Cantabrian Sea or North Atlantic, typically caught by hook and line. If the species is not named specifically, assume the cheapest option in that category.

The pack medium. Water and soy oil are supermarket-aisle signals. Extra virgin olive oil is a fish-first signal. Sunflower oil and refined olive oil fall between, common in mid-range European tins that are meant to be eaten either way.

The form of the fish. Flaked or chunk fish is engineered for mixing. Whole fillets, whole small fish, or intact loin pieces are engineered for a plate.

The price per ounce. Loose pennies per ounce is firmly supermarket-aisle. A dollar or two per ounce is the gourmet-but-accessible middle: Wild Planet, Matiz, Nuri, entry-level Portuguese and Spanish brands. Several dollars per ounce and up is the premium fish-first tier: Ortiz, Pinhais, Olasagasti, Conservas de Cambados.

The can itself. Pop-top lids, printed directly on the can, stacked in the supermarket-aisle: ingredient fish. Pry-open lids, paper or boxed labels wrapped around the can, glass jars, decorative tin art, numbered editions: fish-first.

Most of the frustration people have with tinned fish comes from buying the wrong tin for the task. Someone who wanted to try the tinned fish thing after seeing a post or article buys Chicken of the Sea chunk light and thinks the whole category is overrated. Someone who wanted to make a tuna salad buys a $15 hand-packed Spanish loin and ruins it by mixing it with mayo. Both people were let down by the category because nobody told them the two tins are different products.

The rule is simple. If the fish is going to be an ingredient in something, buy a supermarket-aisle tin. If the fish is going to be the thing you're eating, buy a fish-first tin. The price difference is not just a quality hierarchy, it is also a complete category difference. Both tins are good at what they're meant for.