I went looking for you and this is what I found.
The spontaneous combustion of acrylic is between 850 degree F and 869 degree F. I hope that your fish never see this.
And, PERSPEX: polymerised perspex is not hazardous except that sharp edges produced by sawing may cause abrasions to unprotected skin. Perspex dust or beads produced through sanding, filing or drilling are hazardous. Loose beads of perspex make floors very slippery. Inhaling fine dust causes the development of pulmonary granulomas. The dust can scratch and irritate eyes.