answer as given to me...

most species of animals on the earth are aquatic (or insect). That takes care of them - they either don't need the safety of the ark or are VERY small.

Reptiles of all kinds that needed the safety of the ark were taken as young as possible -- that way they would be small.

Many animals, as we currently know them in their diverse states, still are the same animal after adaptation -- wolves to dogs, all horses, etc.

Clean-up and feeding was aided by the "fact" that God caused all to "sleep" throughout the time.

Some of this according to the account, other according to what I was told.


I'm not vouching for the plausibility, just answering the question as asked.