To find the number of tetras the aquarium can house, we need to divide the total amount of water in the aquarium by the amount of water each tetra needs.
Total number of tetras = Total amount of water / Amount of water per tetra
Total number of tetras = 1×10^5 gallons / 1.25 gallons
Total number of tetras = 8×10^4 tetras
Therefore, the aquarium can house 8×10^4 tetras.