2,291. Worms in Fish

Maachalos Assuros 2:17

If a worm is found in a fish’s stomach, an animal’s brain or in meat, it is prohibited. If salted fish turns wormy, the worms in it are permitted. This is like fruit that has become wormy after being detached from the ground. The salted fish may be eaten along with the worm in it. Similarly, if water in a vessel produces swarming things, they may be drunk along with the water as per Leviticus 11:9, “Anything that has fins and scales in the water, seas, and rivers you may eat.” We infer that we may eat those that have fins and scales in the water, seas, and rivers but not those that do not. Creatures that form in vessels are permitted regardless of whether they have fins and scales or not.

Maachalos Assuros 2:18

Cisterns, trenches and caves are not flowing water, they’re collected water similar to the water in vessels. Therefore, swarming things that form there are permitted. One may bend down and drink without hesitation even though he swallows these little swarming things when doing so.