דברים, פרק י״ד, פסוק ט׳

Aquatic creatures permitted for consumption must possess two distinct physical features: fins, which enable the creature to swim, and scales, which cover its body [ביאור שטיינזלץ]. The repetition of these dietary laws in the book of Deuteronomy, having already been outlined earlier in Leviticus, presents an interesting puzzle. When the Torah repeats the laws concerning land animals and birds, it typically introduces new details or previously unmentioned species. However, the laws regarding aquatic life appear to offer no new information, leaving scholars to wonder about the purpose of this exact restatement [רא״ש, דעת זקנים].

Beyond the repetition of the laws themselves, there is a stylistic repetition within the commands. The text explicitly permits eating creatures with the proper signs and immediately follows by forbidding those without them. This double phrasing is a common feature of biblical language, used primarily for emphasis. It stands in contrast to the later, more concise style of Jewish legal texts, where such a positive and negative formulation might cause confusion regarding a creature that possesses only one of the required signs [ברכת אשר על התורה].

Careful attention to the phrasing reveals additional legal boundaries. The specific reference to creatures living in general bodies of water excludes those developing in closed or artificial environments, such as pits, caves, or man-made vessels. In these isolated water sources, the standard requirement for both fins and scales might not apply in the exact same way [אדרת אליהו]. Furthermore, the close placement of the permission to eat pure aquatic life right next to the prohibition against eating impure ones yields a unique ruling. If a pure fish is swallowed by an impure fish and is later found inside its stomach, the swallowed fish retains its pure status and remains completely permitted for consumption [קיצור בעל הטורים].