Seasonal changes in condition indices in adult mature and non‐maturing burbot, Lota lota (L.), in the north‐eastern Bothnian Bay, northern Finland

Abstract

The population structure and seasonal changes in condition factors of the burbot in a shallow coastal region of the north‐eastern Bothnian Bay are described. The significance of the so‐called rest years is examined by comparing condition indices in immature or sterile and mature burbot. The somatic condition index (K2), liver index (K1), intestine index (K1) and gonad index (Kg) are determined monthly in terms of organ weight in relation to body length. Approximately 30% of the whole catch of 1052 burbot were non‐maturing but were 40 cm or more in length. K2, K1 and K1 were lowest in the autumn, when the first sign of gonad recrudescence was observed in mature burbot. The non‐maturing burbot were never in poorer condition than mature ones. As mature and non‐maturing burbot dissipated their energy stores during the warmest period of the summer, it is concluded that burbot spending a rest year do not accumulate and store energy reserves over the summer for the next year, and that such rest years, if they exist, do not occur for nutritional reasons.