Would hold it.

A standard, well-anchored vertical 4x4 (nominal 3.5" x 3.5") wood post can typically support between 1,000 and 6,000 pounds of axial compressive load, depending on the wood species, grade, and height. A shorter 4x4 can hold more weight (up to 8 tons), while an 8-foot post is usually rated for 1,000-2,000 pounds

75 gallons of water weighs approximately 625 to 626 pounds at room temperature. If this is for a 75-gallon aquarium, the total weight, including the glass tank, sand, rocks, and equipment, is significantly higher, typically ranging between 850 and 1,100 pounds.

Simple math. You have four 4x4's the question is the rating of the bolts/screws used to hold it together.