Mbh 3.186.2b

And although the tank was two yojanas in length and one yojana in width, even there, O lotus-eyed son of Kunti and ruler of men, was no room for the fish to play about! And beholding Manu it said again, ‘O pious and adorable father, take me to the Ganga, the favourite spouse of the Ocean so that I may live there; or do as thou listest. O sinless one, as I have grown to this great bulk by thy favour I shall do thy bidding cheerfully.’ Thus asked the upright and continent and worshipful Manu took the fish to the river Ganga and he put it into the river with his own hands. And there, O conqueror of thy enemies, the fish again grew for some little time and then beholding Manu, it said again, ‘O lord, I am unable to move about in the Ganga on account of my great body; therefore, worshipful sir, do thou please take me quickly to the sea!’ O son of Pritha, Manu then taking it out of the Ganga, carried it to the sea and consigned it there. And despite its great bulk, Manu transported it easily and its touch and smell were also pleasant to him. And when it was thrown into the sea by Manu, it said these words to him with a smile, ‘O adorable being, thou hast protected me with special care; do thou now listen to me as to what thou shouldst do in the fulness of time! O fortunate and worshipful sir, the dissolution of all this mobile and immobile world is nigh at hand. The time for the purging of this world is now ripe. Therefore do I now explain what is good for thee! The mobile and immobile divisions of the creation, those that have the power of locomotion, and those that have it not, of all these the terrible doom hath now approached. Thou shall build a strong massive ark and have it furnished with a long rope. On that must thou ascend, O great Muni, with the seven Rishis and take with thee all the different seeds which were enumerated by regenerate Brahmanas in days of yore, and separately and carefully must thou preserve them therein.