Thymallinae

Thymallinae is a subfamily of freshwater fishes within the family Salmonidae, comprising the graylings, a group of salmonids represented by the genus Thymallus. In some classifications, graylings are treated as a distinct group at the subfamily level to reflect their differences from other salmonids, while in others they are placed within broader Salmoninae.

They are native to cool, clear waters of the Northern Hemisphere, with species found in Europe, Asia, and North America. Graylings typically inhabit rivers, streams, and lakes that are well oxygenated and have clean, gravelly bottoms. They are usually small to medium-sized and have a slender body with a relatively large dorsal fin. Coloration varies but often includes muted greens, browns, or silvery hues, with fins that can show olive or reddish tones.

Ecology and diet vary with life stage, but graylings are generally opportunistic feeders. They rely on aquatic invertebrates, such as insect larvae, as well as small fish and occasional plant material. Juvenile graylings commonly start with invertebrates and shift as they grow toward a more diverse diet.

Reproduction occurs in gravel-bottomed, fast-flowing streams, typically in autumn or winter. Eggs adhere to the substrate and develop over winter, with fry emerging in spring and moving to nearby habitats as they grow. Many populations exhibit seasonal movements related to spawning and foraging.

Taxonomically, the extant subfamily includes the genus Thymallus, with species such as the European grayling (Thymallus thymallus) and the Arctic grayling (Thymallus arcticus). Some classifications also reference fossil genera within Thymallinae. Conservation concerns arise for several grayling populations due to habitat degradation, water extraction, pollution, and introduced species, prompting management and restoration efforts.