Canned, Salted and Smoked Fish

Preserved fish is the category where the identification problem meets a second one: everything else in the tin.

Skin-on is the control

Start with the good news, because it is a design decision rather than a burden.

Mackerel, salmon and other kosher fish preserved with their skin on, so that fin and scale can be checked, are kosher — provided the tin contains no oil or other material of doubtful status.

The contrast is sharp. Fish pieces cleaned of skin and bones may not be used without certification, even where the pack states the species, because some among them may be from a non-kosher fish. The same applies to anchovies and anchovy-flavoured preparations, some of which are produced from non-kosher fish outright.

So for a canner the question is partly a specification one: does your process preserve the evidence, or destroy it? Skin-on packing keeps the product self-verifying.

Where a tin does carry certification but the signs cannot be seen on the fish inside, the position recorded is that the certification on the tin suffices — though some hold it is better where the signs can actually be seen on the fish.

Tuna: the concrete case

The general warning that fish names prove nothing has a specific, well-documented instance here.

More than ten species of fish are sold under the name "tuna", and most of them are not kosher.

Which means the word on the tin is not evidence of anything at all. Canned tuna should be used only with certification and supervision of its production — not because tuna is suspect as a fish, but because "tuna" is not a species, it is a market category.

Sardines sit differently: they are generally made from kosher fish and the practice to eat them is widespread. But some are produced in unsupervised plants, and some contain other materials entirely. Where certification is unavailable, the fallback is to check the fish for fin and scale and to verify what it is packed in.

The oil is a separate question

This is the item most likely to be overlooked, because the fish is what everyone is looking at.

Where fish is packed in fish oil — even where the label says "natural oil", and even where the fish itself is kosher — the oil may come from non-kosher fish. Some tins also carry oil suspected of being made from non-kosher animal fat.

Where the producer states the oil is olive or another vegetable oil, some are lenient, on the reasoning that a declaration of 100% pure vegetable oil can be relied on because a craftsman does not spoil his own trade.

And then the qualification that matters: where there is concern of falsification, one must be stringent unless there is proper certification.

That is worth dwelling on, because it is the same structure as every food-fraud question. The reliance is on a producer's interest in his own reputation. It holds exactly as long as adulteration is not economically attractive — and fails precisely in the categories where it is.

The processing aids nobody declares

Three documented cases, and all three are invisible on a label.

None of these is an ingredient in any sense a buyer would recognise. Two are enzymes — which is the same structural problem as processing aids generally — and the third is a feature of the equipment rather than the formulation.

Salted fish carries a fourth risk that is purely commercial: cheaper fish substituted under the name of an expensive kosher one. The substitute may not be kosher at all. Economically motivated adulteration and species substitution are the same problem wearing different labels.

Bishul akum in a cannery

Fish canned in non-Jewish plants raises the cooking question, and the range of views is worth knowing because the lenient reasoning is specific to industrial production.

• Stringent: some forbid canned fish cooked by non-Jews.
• Lenient for small sardines: they are not important enough to be served at a king's table, so bishul akum does not attach.
• Lenient generally, on industrial grounds: some permit all kosher fish cooked in non-Jewish plants, reasoning that the cooking is done by steam rather than by fire, and further that it is done by electricity rather than by human power.

That third argument is the interesting one, and its reach goes well beyond fish — it is a claim about automated cooking as a category. Note the condition attached even by those who permit: the tin's contents and the oil's status must still have been checked. And where the fish is of a kind not served on the tables of kings or nobles, or not put before guests, there is room to be lenient in any case.

How this interacts with who lights the fire is worth settling with your certifier rather than assuming.

Worms, particularly in farmed fish

Many fish carry forbidden worms picked up in the water or afterwards, and they need thorough cleaning. The modern concern is specifically pond-farmed fish, and carp above all — in hot weather worms are found on the head and tail, in the fins and inside the mouth, even while the fish is alive.

The account given is that they originate outside the pond, a pair gets in, and they multiply until the water is full of them, settling on the fish to feed. Cleaning is by soaking in salt solution or vinegar, then scraping and washing thoroughly — the skin, the head, and particularly around the mouth and fins.

One distinction is worth knowing for inspection purposes: worms found in the intestines are forbidden, because they came from outside. Worms between skin and flesh, or within the flesh, are permitted, because they grew from the fish itself.

Fish and meat on the same site

Fish and meat may not be eaten together, and that restriction reaches production:

• Not cooked together, including with poultry or goose fat.
• Not roasted together — and specifically not in a closed oven of less than four amos, since matters of danger are treated more strictly than ordinary prohibitions. Bedieved, roasting together does not forbid.
• Not salted together. The reason is a sequencing one: the fish release their brine before the meat releases its blood. Where they were salted together, the meat is permitted and the fish must be peeled to the depth of a peel — unless they were in their scales, in which case they are permitted.

For a plant handling both, that makes oven and salting-station allocation a real design question rather than a housekeeping one.

These are general principles, not a ruling on your product. What your specific line requires is a question for your certifying rav and your coordinator.