ummm...10 000 seems a little gishy but wtv....id put 4 giant snakeheads in there...and umm ure 125 gallons seems to have a weird set of fish it it...arowana and giant snakehead...kinda strange...considering a giant gets to 3 feet and plus...that aint gonna last..well nothing in there would...so id just put him with ure 7 incher in the huge pond...and add a couple more...or ure gonna end up with dead fish quik...so unless ure thinkin of buying a 300+ gallon tank for the snakhead u got no choice..and same goes weith the arowana..needs bigger space