Your floor joists are bigger than a 2x4 , probably a 2x10.
yes your floor will hold it, go for it.
I always love seeing this question asked.
When buildings are built and stocked with drywall, the drywall is usually stood up in stacks along walls.
I've seen stacks of over a hundred a million times, so you are talking 5000 pounds, sometimes 7500 of its 5/8 thick.
A 125 fish tank is heavy, lets say 1500 pounds. Would you get worried if you had a party and 10people were standing in that room and the weight was 2000 pounds? No.
Go for it and don't worry about it.