The more visible a fish is, the greater chances they will get eaten. Your pond is very shallow, so you will have a lot of predation, no matter what you put in there - I would stick with natives that can populate the pond based on natural predation.
Again - why are there no fish in there ? Sounds like somebody made this not too long ago, with a similar idea, and fish just have not populated it yet. If it were a natural pond, there definitely would be natives in it.