It depends on how literal you want to take the details we do have. "He made it all in six days." Ok, sure. "On this day he made the animals, on this day the plants, on this day the fish, etc." Was it all the animals? All the fish? No mention of reptiles or amphibians; do we assume those are lumped in with one or the other, or do we assume there was some amount of darwinesque development at hand? It doesn't say for sure, so it's fair to go in either direction I guess. Again, I do take it literally at face value, but I can see why some people wouldn't