Come on guys, you wouldn't bring a newborn home from the hospital and put it to sleep in a king-size bed... As tongue33 says, it will be easier to care for a baby in a smaller environment.
Muhammad, I understand you've been told it's an Australian Arowana. Here is a page that has information on water temperatures, and such.
http://www.aquaworldnet.com/awmag/a_3aroen.htm
It says that bloodworms are a good food for babies. I think that frozen ones might be more nutritious though.
Have you kept many fish before?
Do you understand how to 'cycle' your fishtank and do partial water changes to maintain good water quality? If you are new to this, I suggest you read everything you can about 'cycling' tanks, filtration and testing/maintaining water paramaters [quality]
I have never had an Arowana... Yet... but my good friend owns a petstore, and he has a beautiful 2 ft. Silver, and we've talked about it much... He recommends good quality pellet food when it is a little bigger, he tries to stay away from live food because it can be less nutritious, although he treats it with freeze-dried crickets [but not for tiny babies]
Does it still have its yolk-sack [the little yellow balloon under it]?