"On the Fish and the Sting": The Complete Guide to Passover Kashrut Laws for Fish

In the past, when we bought fish, we could simply go to the local market, choose the fish we wanted to prepare for our holiday or Shabbat meal, and on the way to the checkout, just verify that it was a kosher fish with signs of purity - fins and scales.

Today, for various reasons, things have changed and become more complicated due to many parasites prohibited for consumption found in kosher fish. Therefore, purchasing fish requires familiarity with basic laws on the subject, in order to avoid consuming forbidden foods. The guide before you will provide you with the basic knowledge required to properly purchase kosher fish for Passover and throughout the year.

In fact, the problem of parasites found in fish has already been discussed in Jewish law in past years, and has come up on the tables of kings, our rabbinical authorities, both early and later commentators. The author of "Beit Lechem Yehuda" (Sec. 84, subsection 37) writes on the subject that "I also see fit to warn about cutting from the head the 'zavernish' (gills), because usually very small worms are found there."

Similarly, the author of "Orach Mishor" writes in his book: "One needs to be careful about this, because it is very common, and I have seen them several times in some types of fish, where types of worms were found in the fish's head, and they are truly as thin as a hair and move around, and there is no doubt that they are noticeable and certainly come from the outside world, and it is a Torah prohibition." He further adds in his book "Zer Zahav" and writes: "It seems that the worms found in the fish's head are a type of leech called 'eagle' - as their appearance indicates."

(Photo: shutterstock)

Today, fish are marketed in two main ways:

a. Open display in fish stores.

b. In sealed packaging at supermarkets.

Additionally, different kosher certifications tend to approach this issue of worms in fish differently, and it's important to distinguish between them:

Stores under local Rabbinic supervision:

You should check with the on-site supervisor if there is indeed oversight regarding worms. Additionally, in practical terms, it's important to know that pond fish such as: red tilapia, tilapia (musht), amur, bass, white bass, mullet, barramundi, silver carp, and common carp sold on site are without concern for parasites, since they grow in treated ponds. However, it's important to know that if we're talking about sea fish or frozen fish from abroad - there is concern for worms.

"Mehadrin" supervision:

a. Pond fish are sold without concern for worms, as we explained above, since they come from treated ponds.

b. It's important to know that sea fish and frozen fish from abroad that come opened, the "Mehadrin" supervision on them cannot help prevent the issue of worms. This is because these are fish that have worms present in their bellies and the like. Therefore, it's important to clean them and be careful about treating the inner part of the fish. 

However, it's important to emphasize that if they come in a sealed package with a stamp from a known and recognized Badatz, clearly stating that there is no concern for parasites - the fish is strictly kosher, even regarding worms.

Caution! Worms in fish flesh:

Despite what has been said so far, there are several specific species of fish where the problem of parasites is more significant, and they are:

1. Golden or pollock

 2. Salmon (except for those imported from Norway and Chile)

3. Sole (except for what is imported from the Netherlands).

(Photo: shutterstock)

The reason for this is that these fish have a high infestation of worms in their flesh. So much so, that there are even strict kosher certifications that consider them forbidden, and refuse to give them their certification. Moreover, you should know that there are well-known kosher certifications that are very strict on this issue, including: Badatz Eda Haredit, the Institute for Mitzvot Dependent on the Land headed by Rabbi Shneur Z. Revach, and Badatz She'erit Yisrael.

In contrast, there is a fish called "Rotbarsch" (red fish), where the process of removing worms must be performed, and the same applies to a type of fish called "Baccala Merluza".

Process for removing worms from fish:

a. After removing the internal organs, check to ensure no "pockets" of parasites remain in the abdominal cavity.

b. Dig about 1.5 cm into the fish flesh and remove the parasite "anchor."

 Good luck!