Wow, that's great, I would love to see that fish! That's really heavy.
An easy way to compress a picture is with PowerPoint. Paste the picture in to a blank PowerPoint Slide, and resize it to fit the standard slide (8 by 10 inches). Select "save as" type JPEG and give the filename. The resultant file will be a highly-compressed JPEG of the original.
Hope this helps. Good fishing.