General "blue fish":
* Ryba niebieska (literally "blue fish") - This is the most common and general way to say it, but it's not very specific.
* Ryba o niebieskim kolorze (literally "fish with blue color") - This is a more precise way to describe a fish that is blue.
Specific types of blue fish:
* Makrela (Mackerel)
* Tuńczyk (Tuna)
* Sardynki (Sardines)
* Śledź (Herring)
You can also use the name of a specific fish species with "niebieski" (blue) before it, for example:
* Niebieski dorsz (Blue cod)
* Niebieska ryba miecz (Blue swordfish)
The best way to translate "blue fish" is to consider the specific context and choose the most appropriate option.