If you want to keep an Oscar, don't keep fish like Arrowana and ghost knifes. Make a choice between what type of tank you want, don't start just stuffing in random big fish or they won't do well.
For that stocking list without the Oscar, figure on about 300 gallons.
For that stocking list without the arrowana or ghost knife but with an Oscar, and even a mate for the Oscar, you can use a 150 gallon tank.
For that stocking list without the Oscar, figure on about 300 gallons.
For that stocking list without the arrowana or ghost knife but with an Oscar, and even a mate for the Oscar, you can use a 150 gallon tank.