This is a sign of His supreme controlling power. Although He comes within the material atmosphere, māyā cannot touch Him. Therefore, no material qualities can be attributed to Him in any degree.
Once, at the end of the previous kalpa, a demon named Hayagrīva wanted to take the Vedic knowledge away from Lord Brahmā at the time of annihilation. Therefore the Supreme Personality of Godhead took the incarnation of a fish at the beginning of the period of Svāyambhuva Manu and saved the Vedas. During the reign of Cākṣuṣa Manu there was a king named Satyavrata, who was a great pious ruler. To save him, the Lord appeared as the fish incarnation for a second time. King Satyavrata later became the son of the sun-god and was known as Śrāddhadeva. He was established as Manu by the Supreme Personality of Godhead.