If your camera has total control, then higher ISO (800 or higher) large aperture (low F#) and by default faster shutter speeds. A lot of times a flash can help, as most fish look better in that color temp anyways.
I never have had luck with a tripod on fish...to many random movements.
After you've fed the fish heavy works well for me...they are full, and really slow by comparison.
Its not uncommon for me to take 20+ pics of one fish just to get 1 keeper.
To "freeze" fish, i.e., eliminate motion blur, you either need a fast shutter speed or to use indirect flash and the fastest possible shutter speed your camera will use with a flash.
It is unlikely that you'll be able to shoot fish in an aquarium without flash. As a rule, there isn't enough light for a fast-enough shutter speed. You can raise the ISO setting to get a faster shutter speed, but images will get noisy with all but the best/latest DSLRs. Opening the lens aperture to its widest setting will help with shutter speed, but makes it difficult to get enough depth of field to keep a sufficient amount of the fish body in focus. No matter what, make sure you keep the eyes in focus.
It looks like the Nikon 5400 has a hot shoe so you should be able to attach an external flash which is key to getting fish shots. My technique is to attach a flash to the hot show and tilt the flash head at 45 deg. I also attach a white card to the flash head. This setup shoots the main flash beam at the ceiling, but sends a considerable amount of indirect light into the aquarium, giving you the lighting you need and avoiding flash glare on the glass.
I then pull up a bucket, choose a spot where a fish habitually stops/turns around, and wait for the fish to show up. Chasing fish up and down the length of the tank will just make you tired. Choose a spot and wait for them.
Shoot at ISO 400 or 800, try to use an aperture of f/8 or f/11, and use the fastest shutter speed you can get. Play around a bit to get the right exposure and you should be able to get the fish shots you want.
This shot was taken with the method described above. Good luck and show us your results.