trout parr by kalel jones

A trout of less than one year old is called a parr. They are recognisably trout now, but have distinctive fingerprints or parr marks along the side which they lose as they get older.

Parr have similar habitat needs to fry: plenty of cover to hide from each other and from predators, especially fish eating birds. They can cope with deeper and faster water as they grow. In order to find their own territory, they will gradually drop downstream with the flow rather than fight their way up against the flow.

It is quite difficult to tell whether a parr is salmon or trout. One clue is the habitat — salmon parr tend to prefer faster riffles than trout as they are stronger swimmers. The diagram below from the Atlantic Salmon Trust, identifies the main differences.

Salmon parr (I) can normally be distinguished from young brown/​sea trout (II) by the more streamlined shape, deeply forked tail, longer pectoral fin, lack of orange on adipose fin, smaller mouth, sharper snout, only 1 – 4 spots on gill cover (often one large spot), well defined parr marks.