Dear Incomplete Salmo Angler,
Save your Salmo specimens for your reference collection even if you can't
be sure of which is which species. Lepiksaar and Heinrich gave some notes
on differences between S. salar and S. trutta - the distribution of pores
of different size on the sides of the vertebrae. I don't find that this
character is always in agreement with my own reference specimens. There is
perhaps another way around the problem. Salmon and trout have different
growth histories. Once the young have left the stream where they hatched
and enter the sea they start growing much faster, especially the salmon.
So if you can identify the annuli you will see the point in life when
growth was increasing rapidly. Then you calculate the fish length at each
annuli of fast growth. Below I give you data on size at migration to the
sea and at each year thereafter:
Salmo trutta
size at seaward migration: 14-25 cm
+ 1 year: 30-40 cm
+ 2 years: 45-60 cm
+ 3 years: 50-70 cm
Salmo salar
size at seaward migration: 10-20 cm
+ 1 year: 50-60 cm
+ 2 years: 70-90 cm
+ 3 years: 90-105 cm
+ 4 years: 110-120 cm
These figures indicate that salmon grows much faster in the sea.
Landlocked populations, like brown trout, has their special lower growth
rates.
Good luck with your reference specimens. The problem you have with these
is the same you have with archaeological specimens.
Leif Jonsson
Göteborgs Naturhistoriska Museum
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