ויקרא, פרק י״א, פסוק י׳

Clear boundaries are established regarding the consumption of aquatic life, disqualifying any marine creature lacking specific signs of purity. Unlike land animals and birds, no specific names of permitted or forbidden fish are listed. This omission stems from the tradition that the first man only assigned names to terrestrial creatures and birds, leaving marine life unnamed [הטור].

The requirement for fins and scales reflects the very nature of these aquatic creatures [רמב״ן והטור]. Fish possessing these features typically inhabit the upper, clear waters. They maintain a degree of natural body heat that repels harmful moisture. Conversely, scaleless creatures usually dwell in the lower, murky depths; their cold and damp nature makes them potentially detrimental to human health. The requirement that these signs be present while the creature is in the water yields an important practical law. If a fish naturally sheds its scales the moment it is pulled onto dry land, it remains permitted for consumption, provided it possessed fins and scales while submerged [בכור שור, חומת אנך]. The criteria broadly encompass various forms of marine life, including creatures with bones that do not reproduce, as well as boneless creatures that do multiply [תורה תמימה, מלבי״ם].

Aquatic life is divided into two primary groups. The first group consists of swarming aquatic creatures. Some understand this as referring to microscopic or worm-like organisms generated directly from the water itself [אבן עזרא, ביאור יש״ר]. Others suggest the terminology emphasizes movement, pointing to low-lying creatures that swarm along the waterbed or fast-swimming fish that reproduce in massive schools [רש״י, רמב״ן, מלבי״ם]. The second group encompasses all other living creatures in the water. This can be understood as larger animals born from a male and female [אבן עזרא]. Alternatively, it refers to aquatic animals with legs that walk on the ocean floor much like land animals in a field, marine mammals such as dolphins and whales, cartilaginous fish like sharks, and amphibians like frogs that mature on land but inhabit the water [רמב״ן, שד״ל, ביאור יש״ר, מלבי״ם, ביאור שטיינזלץ].

Within this broader category of marine animals, commentators also address a wondrous creature known as a siren, described as having the upper body of a human and the lower body of a fish [רמב״ן, מלבי״ם, אדרת אליהו, אם למקרא]. Based on the testimonies of ancient seafarers and naturalists, the sages analyzed the status of this creature. They concluded that while it exhibits human-like features, it is classified as an animal; therefore, its corpse does not impart ritual impurity to a shared enclosure in the way a human corpse would.

All aquatic creatures lacking the signs of purity are classified as detestable rather than ritually impure [רד״צ הופמן, רש״ר הירש]. This specific distinction indicates that their carcasses do not transfer physical impurity through touch; the restriction is exclusively focused on consumption. The concept of detestability here conveys a profound moral and spiritual revulsion. These creatures are not inherently evil, for God created them [ביאור יש״ר]. Rather, for the Israelites, who are tasked with maintaining spiritual purity, consuming them is considered an abomination that directly contradicts their pursuit of holiness [העמק דבר, רש״ר הירש]. The spiritual impact is so severe that even eating them unintentionally defiles the soul [אור החיים].

Practically, this intense restriction applies not only to the flesh of the creatures themselves but also to any brine, sauce, or liquid extracted from them, provided it imparts a noticeable flavor to other food [תורה תמימה, מלבי״ם]. Yet, despite this strict dietary prohibition, the creatures are only detestable for consumption. An individual is permitted to derive economic benefit from them, such as selling them for profit, as long as this is done casually and does not become a permanent commercial enterprise dealing in forbidden foods [תורה תמימה, רש״ר הירש].