Does the burbot, Lota lota, have rest years between normal spawning seasons?

A large number of sterile burbot (Lota lota) have been recorded on the northern coast of the Bothnian Bay (29–93%) and in Lake Kemijärvi in northern Finland (44%). A suggested hypothesis is that the burbot needs one or more rest years between spawning seasons to restore the fat reserves in its liver. A comparison made here between the three burbot populations (brackish water, lake and river), did not confirm this hypothesis. The somatic condition index, liver index and intestine index of the normally‐spawning river burbot, in which the percentage of non‐spawning fish was 14%, were considerably lower than those in spawned or sterile coastal or lake burbot, so that poor nutrition state did not result in sterility or rest years.