h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

"Another subspecies never travels to the ocean and is commonly referred to as 'landlocked' salmon. The Atlantic salmon can be easily distinguished from other Osteichthyes by their silvery colour, their characteristic of being spotted and deformed during the spawning season, small scales, a round dorsal fin, and their comparatively large size1. Landlocked salmon exist in a wider variety of colours than seagoing salmon, such as black and green, do not become as deformed, and are generally much smaller. The bodies of all salmon are thin and long, allowing them to travel upriver more easily."

This may be relevant in North America, but has no meaning in the UK. Yes there are a very, very few male salmo salar that to do not migrate in the UK known as “precocious parr”. This does not make them a sub-species, but a perhaps just natural adaptation of the population. There is no known self sustaining population of land-locked salmo salar in the UK.

As for all salmon being “thin and long”, I suggest your previous author take another look at the species. The only time they are thin and long is as a “kelt”.