There are two different variants of Ruda, Sjöruda and Dammruda.
It thrives in both running and stagnant water, fresh water and brackish water.
Rudan is found in Skåne, Blekinge, Gotland (including Tingstäde swamp, Storsund and Fardume swamp), Bohuslän, Dalsland (10 lakes), Vänern, Västergötland, Närke, Västmanland, Södermanland (Trehörningen in Huddinge sn), Värmland, Dalarna, Jämtland and from the coast of Småland north all the way into Norrbotten, where it is found in some lakes at the marine border in Pajala and Junosuando snr, as well as in the archipelagos of the Baltic Sea and the Gulf of Bothnia.
It is very durable and can handle many different environments.
Although it is a hot water fish, it can survive in lakes in Lapland by lying and pressing against the mud at the bottom of a lake that has not frozen.
For play, the rudder can hike up from the coastal brackish water to fresh water and back again.
The species can be over 40 years old.
Swedish record: 2.8 Kg.