For fluorescence photography, you need a filter on the light source to limit the output to the excitation wavelength, and you also need a second filter on the lens to remove the excitation wavelength, and only allow the emitted light. You are trying to photograph the light that has been re-emitted by the fluorescent organism. If you allowed the excitation light to reach the camera, it would over power the weaker fluorescence signal that are being emitted by the various organisms. So, as Bill says, you need filters at both the light source and the camera, albeit different wavelength filters at each spot. I hope that makes sense.
Ahhh yes! I did not understand how the excitation filters on the strobe would help rather than overwhelm the lighting from the organism.. .but now it makes sense. Thank you!!!