basically it isn't going to happen with an all in one.
photographing a mirror is a good simile the lense and flash are a couple of cm apart pointing in exactly the same direction - no surprise that all the flash is coming straight back.
you could try a diffuser (a fag paper is ... well a fag paper - a diffuser has depth (3 or 4 layers of greaseproof paper should do it) - it doesn't lessen the power ... it scatters the light)
the only way to photograph a mirror is to light it from the side(s).
there is a technique called painting which uses a torch .... but you need to be able to keep the shutter open for a few seconds
A couple of very bright torches (the 1,000,000 candle jobs) with diffusers (to stop the reflectors creating bright spots - you'll have to experiment - cause of course a fish isn't flat ... so the angles will be different.
http://www.sublime-light.com/index.php/2007/07 /27/portrait-lighting-for-beginners-portraits- with-one-light/
http://www.stevesphotoshop.co.uk/