I have to say YES. I'm certainly not trying to cause you trouble but I'm sure Mort could get his snout and part of his head into something that size. Please get rid of this before you wish you had. Send me the dimensions of the inside lip of the aquarium and I'll cut you a frame out of screen making aluminum. I'll also send with it the screen material. All you will have to do is take it somewhere to get the screen material installed. It must be installed loosely or it will twist the frame and the finished lid will not sit flush on the inside lip.
If this is something you want me to do simply get the measurements(tight measurement) I'll take a 1/16th off those measurements so it's not too tight. PM me the info. and your name and address and I'll get it out to you ASAP.