Matsya avatara, to protect Manu...

Verse 1.3.15:
Recap: First chapter, questions of sages to Suta Goswami.
Second chapter, Suta Goswami is answering questions of the sages
Third chapter, He is explaining the different incarnations of the Lord. Today, we are reading about the Supreme Personality of Godhead, when he took the form of a fish. When the whole world was in inundation, he protected Vaivasvata Manu and the different other creatures during this whole inundation.

Since we are talking about Manus, we will reflect on them a little more:
There are as we all know, 4 yuga's: satya, treta, dwapara and kali
kali is 432000 years
dwapara 864000 years
treta 1296000 years
satya 1728000 years
Total: 4 million 32 thousand years = 4.32 million years
1 day of brahma: 1000 such cycles of 4 yugas
1 night of brahma: 1000 such cycles of 4 yugas
1 year of brahma: 365 such days
Brahma lives for 100 such years

A Manvantar (change of a Manu) takes place every 71 x 432000 solar years. One day of Brahma is equal to such 14 Manus plus 15 times the age of a Satya yuga. This duration of one day's time in the life of Brahma, is called a Kalpa.

At present it is the regime of Vaivaswata Manu.

....

The reason we came to the material world is that we are in a prison house, to purify ourselves. From Brahma's point, if we are Krishna Conscious for a moment, then we can get out of this material world. It is really a big opportune moment for us.

Analogy: Ants busy building an anthill. For us, if a small rain comes, it is completely destructed. Same thing we need to know to, this life is very short and we have a golden chance to easily get out of this material world. Wrt the demigods lifetime, ours is a moment. But due to Srila Prabhupada's mercy, just in this life time we can get out of this cycle of birth and death. So, in a moment in the demigod's lifetime. Therefore, We need to sincerely chant, be in the association of devotees and serve them.