Relationship between Food, Fat, Sexual Maturation, and Spawning Time of Baltic Herring (Clupea harengus membras) in the Archipelago Sea

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Abstract
The effect of nutritional status on gonad maturation and timing of spawning was examined in the Baltic herring (Clupea harengus membras) in the Archipelago Sea. Fish were collected from overwintering areas in December and from the spawning grounds in May–July. Muscle fat content, amount of mesenteric fat, and condition factor were used as indicators of nutritional status of fish. In winter, fish were highly variable with substantial individual variation in nutritional status, gonad stage, gonad weight, and gonadosomatic index (GSI). Gonad weight was related to fat content, suggesting a close relationship with fish nutritional status and maturation rate. Spawning fish were separable into early and late spawners according to fat content, gonad weight, and GSI but not according to length. The spawning shoals consisted of mixtures of fish of all sizes. I concluded that in the study area, individual maturation cycles vary and timing of spawning is primarily determined by the feeding conditions prior to spawning.