“Goldfish” is most commonly translated as “poisson rouge” in French, litteraly “red fish”, but if the golden colour is meaningful and was to be preserved, another name of that same fish is “cyprin doré”.
The article before the name of a piece of art is not mandatory, and it may either be added or left out. My personal preference would be to leave it out, but opinions vary.
To show some examples, the French poet Paul Verlaine published Fêtes galantes (without the article) and Les mémoires d’un veuf (with the article).
Also, the first word of a title that is not an article may also be capitalized or not. Some recommend it is, but some are more flexible and allow either. The words after that usually start with a lower case letter in French (unless it is a proper name, of course, but it is not the case here).
So, in the plural form, any of the following could work:
- Cyprins dorés / Poissons rouges
- Les cyprins dorés / Les poissons rouges
- Les Cyprins dorés / Les Poissons rouges