Instead of operating the camera in 'P' mode where exposure and aperture are camera sensed, I set it into the Tv mode where I control the shutter speed. I had it @ 1/2500 of a second and the flash adjusted down.
Here, a Pseudogastromyzon cheni is caught in panicked take-off mode as a female Sewellia comes zooming in defending the food rock.

Close up of serious tuberculation.
Side view.
Here's the evil algae-defender in closeup.
Gastromyzon stellatus enjoying algae of another stone.
I've added this pic to the species profile.
I'm sure the fast shutter speed is yielding sharper detail so I'm going to do some more experimentation using this camera mode. I'm still using auto-focus.
Martin.