For macro shots, you need to switch into manual mode.
Set the shutter for 1/150 or so and the aperture to F 4.0 atleast.
That will 'freeze' the fish and increase the depth of field so that
if the fish is at an angle, the whole thing will still be in focus.
Depending on your light, you may need an external flash.
If you don't have an external flash, and your pictures are coming
out too dark with these settings, try F 3.0 and shutter 1/80 though
that may not work AS well as the other shots.
Compare these pics...
Top one, with autofocus, point&shoot setting, no flash
Bottom one with autofocus, manual settings, F Stop 4.0, 1/150, external flash
Notice that in the bottom picture everything is in focus whereas in
the top one, the eggs/leaf closer to the camera is blurry.
Photos taken with Sony DSC F707