בראשית, פרק א׳, פסוק כ׳

Creation ascends a profound step as the world prepares to welcome animal life. After the previous days laid down the infrastructure of sky, sea, and dry land, and adorned the earth with vegetation, the fifth day introduces the breath of life for the very first time. This mirrors the second day of creation; just as the waters and the sky were formed then, those vast expanses are now filled with their inhabitants [רש״ר הירש, קאסוטו]. The divine command calls for the waters to swarm, sparking a reality of constant movement, eagerness, and massive multiplication. The once-still waters suddenly teem with countless creatures darting in every direction, giving the illusion that the water itself is alive and moving [רמב״ן, רד״ק, שד״ל, קאסוטו]. From another perspective, this swarming refers to any low-lying creature that does not rise high above the ground, a category encompassing everything from insects and rodents to fish [רש״י, מזרחי].

The exact role of the water in this process is a matter of discussion. Some commentators view the water as the actual raw material from which these creatures were produced, receiving a direct command to give birth to them [אבן עזרא, רלב״ג, אברבנאל]. Others maintain that the water merely served as the arena for this burst of life, with the swarming simply describing the rapid movement of the animals within their aquatic environment [שד״ל, רס״ג]. As these creatures emerge, they are distinctly characterized by a living soul. This sets them apart from the vegetation created on the third day. While plants possess a force of growth, they lack true vitality, sensation, independent will, or the ability to move on their own. The emphasis here is on a soul imbued with genuine life [רש״י, רמב״ן, רבנו בחיי, רס״ג]. Thus, while the physical swarming represents the external action of movement, the living soul embodies the internal essence and will of the creature [רש״ר הירש].

Alongside the aquatic life, birds are brought into existence to fly above the earth. A well-known tension exists regarding their origin, as the initial account links their creation to water, while a later account implies they were formed from the earth. The primary resolution is that birds were fashioned from marshland or mud—a unique mixture of water, earth, and air. Because their composition falls exactly between that of aquatic fish and land-dwelling animals, birds share characteristics of both, a biological reality even reflected in the specific laws of ritual slaughter [רמב״ן, כלי יקר, מלבי״ם, תולדות יצחק, אברבנאל]. Their flight is characterized by constant, multi-directional movement [רש״ר הירש, קאסוטו], which can also be understood as two distinct types of flying: hovering low near the ground and soaring high in the upper atmosphere [העמק דבר, אדרת אליהו]. As they fly across the expanse of the sky, they occupy the lower atmosphere visible to an observer below, appearing to glide against the backdrop of the sky's dome [שד״ל, קאסוטו]. Furthermore, the very beating of their wings serves an ecological purpose, cleansing and purifying the earth's air from excess moisture descending from above [ספורנו].

Curiously, the familiar declaration that things were completed exactly as commanded is absent from the narrative of the fifth day. One explanation for this omission is that the creation of the animal kingdom was a continuous process that spanned two days, only reaching its full completion on the sixth day [קונטרס חיבה יתירה]. Another perspective suggests that the initial creations of this day, specifically the massive and destructive sea monsters, did not remain in their original state. To protect the world from being overrun by their sheer power, God intervened by removing the females of the species. Because this specific aspect of creation was fundamentally altered to ensure the world's survival, the reality did not remain exactly as it was initially formed [אברבנאל, צאינה וראינה, קאסוטו].