How to keep the original shape of applets on the panel (Diodon)

I like Diodon very much as a clipboard application.
It is simple and not so complicated as copyq to use.

But one thing annoys me. When I change desktop theme, its fish-like icon often disappears from the panel. Instead some dull icon appears there.

Please let me know how to keep the fish-like icon of Diodon whatever theme I may choose.
(Some sites tell us ways to do so. If possible, I would like easier way not to use commands on the terminal.)

The fish icon of Diodon came back.

Appearing or disappearing of this icon seems to depend on how to arrange or customize a theme.
On choosing a certain pattern of icon, the fish came back to my satisfaction.
I prefer this fish-shape icon to that of a simple paper clip.

yes, and not all icon themes have an icon for specific applications. You can copy the 'good' icon into the same place on the theme you want to use.

Hi, mickee
Thank you for your kind advice.
My way is not so good as yours.
Several days ago I replaced all the Diodon icons by those of fish-shape.
So on my panel always appears the fish icon instead of a dry paper clip, concerning Diodon .
I prefer this fish icon. It has a funny appearance but is a lovely look to me.

Thank you again.