Trademarks: I Have a Design Patent; Do I Still Need a Trademark

Hi,
I have a Design Patent on the appearance / design of a clock face.

I am now manufacturing the product, and have been selling it online and in stores for around 5 years.

Let's say my product name is "Fish Clock"...

My website and all selling brochures etc refer to the product as the Fish Clock.

I don't have a Trademark on Fish Clock, and no-one else does.

If someone else trademarks the name, would they still be able to stop me from selling my product?

Many thanks.

Trademarks: I Have a Design Patent; Do I Still Need a Trademark