FIG. 1 is a perspective view of a lamp for an aquarium showing my new design;

FIG. 2 is a front elevation view thereof, the rear view being a mirror image of FIG. 2;

FIG. 3 is a left side elevation view thereof, the right view being a mirror image of FIG. 3;

FIG. 4 is a top view thereof;

FIG. 5 is a bottom view thereof;

FIG. 6 is a perspective view of a lamp for an aquarium that is hung up; and,

FIG. 7 is a perspective view of the lamp on the top of an aquarium.

The broken lines shown on the drawings are for illustrative purposes only and form no part of the claimed design.