Reviews in Fish Biology and Fisheries 11: 171–179, 2002.
© 2002 Kluwer Academic Publishers. Printed in the Netherlands.
The origin of the salmonid ﬁshes: marine, freshwater ...or neither?
National Institute of Water and Atmospheric Research, PO Box 8602, Christchurch, New Zealand (E-mail:
Accepted 10 April 2002
Abstract page 171
Diadromy in Salmonidae
An historical perspective on opinions regarding the origins of the Salmonidae 172
The geochronological place of diadromous species in salmonid history 174
Diadromy and phylogenetic analysis 174
Origin of Salmonidae in a cladistic context 175
Relationships of salmonids in the context of variability of diadromous life cycles 176
Key words: diadromy, freshwater, marine, origins, Salmonidae
The evolutionary origins of the salmonid ﬁshes, whether in freshwater or the sea, have been debated for
centuries. Early views favoured a group of marine ancestry invading freshwaters; more recently, there was a shift
towards a freshwater ancestry, on grounds that a return to freshwater to spawn indicates the ancestral biome.
Salmonids are widely believed to share an ancient common ancestry with the northern hemisphere Osmeridae
and southern hemisphere Retropinnidae and Galaxiidae. Salmonidae are diadromous, as are Osmeridae,
Retropinnidae and Galaxiidae. This suggests that diadromy is an ancient behavioral phenomenon across all
these groups, that the shared common ancestry of these groups was also diadromous, and that the ancestry of
Salmonidae was neither marine nor freshwater, but was amongst diadromous ﬁshes. This begs the question of
whether this common ancestor was marine or freshwater, a question for which an answer seems likely to be elusive.
The question of whether ﬁshes of the family
Salmonidae have a marine or freshwater ancestry is
a venerable one that has been discussed often and
for decades. It has attracted the attention of some
great ichthyologists of the past, and continues to
attract comment. Opinions, summarized across nearly
two centuries, seem evenly divided over the answer,
though perhaps support has shifted from a majority
early belief in a marine origin, towards a freshwater
ancestry during more recent decades (see below).
The question has been so intriguing probably because
of the apparently deep-seated (and usually correct)
notion that freshwater ﬁshes are generally unable to
make a transition to marine habitats (or marine ﬁshes
make the reverse transition – though this seems to have
been of less interest) and yet salmon and trout can
move, seemingly freely, between these two biomes.
That there has been so much debate about salmonid
origins is perhaps enigmatic, given lesser interest in
the same question for other ﬁsh that move equally