By Rabbi Yair Hoffman

What halachic discussions revolve around salmon? Can an entire shiur be devoted to this one topic? Yes, indeed. Here’s a four-part halachic look at salmon.

Star-K vs. OU

The first topic is the debate between the Orthodox Union and the Star-K about the kashrus of farmed salmon that are packed in fillets without any skin. Generally speaking, kosher fish are identified by having fins and scales. As long as the scales fit the halachic definition of a scale, the fish can be identified as kosher solely on the basis of the presence of the scale (see S.A. Y.D. 83:1).

Rav Moshe Feinstein, zt’l, ruled that salmon’s uniquely colored pink flesh would constitute a siman muvhak that it is kosher (as only salmon and trout have pink or reddish flesh). Based upon this, there would be no need to actually examine the skin for scales or scale marks. The ruling was conveyed to Rav Belsky, zt’l, by Rav Nota Greenblatt, zt’l, one of Rav Moshe’s leading talmidim.

Subsequently, however, it was discovered that the flesh of salmon is not naturally pink. It is actually white. What makes salmon flesh pink? It is their consumption of an antioxidant called “Astaxanthin,” a carotenoid pigment that occurs in microalgae, krill, plankton, shrimp, and among other sea creatures. For farmed salmon, the astaxanthin is added to the feed in one of two ways:

  • They add crushed lobsters to the feed.
  • They add astaxanthin artificially. There are federal guidelines forbidding adding more than 72 grams per ton (see FDA Title 21 Sec. 73.35).

The question arises as to whether the ruling of Rav Moshe, zt’l, would still apply to the farmed salmon with the added-in artificial astaxanthin. Rav Belsky, zt’l, ruled that the finances involved in creating such an infrastructure would also create a “siman muvhak.” Rav Heinemann, lbc’l, however, ruled stringently. On account of this, the Star-K does not allow Costco fillet salmon at their catered events.

This author asked Rav Heinemann to what extent he is machmir. Is there a requirement, say, to kasher the oven as well, as would be the case with a non-kosher fish? Rav Heinemann ruled that there is no need to kasher the oven.

Pouty Fish

The second topic under discussion deals with something that is about to come to market. (It was supposed to come to market two years ago, but the pandemic derailed it.)

Generally speaking, farmed salmon is sold when it reaches 12 to 18 pounds in size. It takes 36 months for the salmon to get to this size. A company called AquaBounty has succeeded in adding different DNA to the salmon that will make it mature much faster. With the newly introduced DNA from other aquatic creatures, it only takes 18 months for the salmon to mature to the necessary size.

The problem is that some of the genetic material introduced is from a non-kosher aquatic creature called an ocean pout. Some of the other material is from the Chinook salmon. An ocean pout is decidedly not kosher, as its scales are not halachically considered kashkeses. The DNA of the ocean pout allows for the “pause switch” on the growth hormone from the Chinook material to stay on. The question is whether this is considered “she’eilah-free” or not.


The third topic involves the anisakis worms found in the flesh of salmon. The sugya is found in the Gemara in Chullin 67b. The underlying question is how we understand the ruling of the Mechaber (Y.D. 84:16) when he states that if the worms are found in the gut, it is not kosher, and if in the flesh, it is kosher. Was this an across-the-board statement? Or do we say that when there is indication that the worms may have migrated from the gut, the leniency does not apply? This author has video footage of the worms migrating from the gut into the flesh. When this question was posed to Rav Elyashiv, zt’l, he ruled specifically that the Mechaber was not referring to such a situation, and it would be prohibited to consume the salmon.

Dark Spots

For years, researchers have been wondering why there are melanin spots, or dark spots, in salmon fillets. It was recently discovered by a company called Nofima and research done at the Norwegian University of Life Science (NMBU) that the causes of these spots are actually rib fractures.

In both freshwater smolt and wild salmon, there was an average of four rib defects per fish. After transfer to sea, the number increased to 10 defects per fish. Dark melanin spots in fillets are the most common quality problem in farmed salmon. Most spots are found in the fillet near the head and abdomen. The increase occurred during the final freshwater period and the first months at sea, and remained stable until slaughter. n


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