"Newly purchased" doesn't help us know the size. But, here's a blurb I posted for another member on starting out juvies. Do a search on african arowana and heterotis niloticus since this subject has come up many times this year.
Basically, the only real success seems to be in providing a constant source of food until the aros reach about 8" and develop some fat storage to allow them to receive scheduled feedings like most other fish.
I raised the young in bare tanks with sponge filters. The sponge filters allow the fish to "graze" on previously missed food until the next feeding. Be sure to rinse of the sponges every other day to keep spoiled food off of them. Keep the water on the alkaline side and at 80 degrees. Also keep a good lid on their tank. They're jumpers from the get-go. They also need a cover to provide matching air and water temps while the young's air-breathing architecture is developing.
Feed them on a variety of small foods. Frozen bloodworms, daphnia, brine shrimp, crumble food, sinking food, cyclop-eeze, flakes, and micro-pellets are all taken. Feed high protein foods since they have high metabolic rates (no cheap generic foods). Water changes of 30-50% need to be done every 2-3 days.
Af aros need to be housed either as 1 to a tank or 4 and up to a tank. With 2 or 3 you'll wind up with only one in short time as their aggression towards each other is high.
Note: my best success was in following the above and allowing my rearing tanks to go green with algae. These are a filter-feeding species, after all, and I think they benefitted from some algae consumption in their diets.
Good luck!!
