Finding home obviously is essential in many animal species (Kirschvink 1997); mammals such as whales (Schofi eld et al. 2008) and seals (Kiyota 2005) undertake long migrations in order to reach mating areas, as do birds (Wiltschko and Wiltschko 2003), turtles (Lohmann et al. 1996) and salmons (Ouinn 1993). A common term for this is “homing”, but what is actually the home of a species? Do migrating birds on the northern hemisphere migrate south to avoid the winter or do they migrate north in the spring in order to breed? The question whether anadromy in salmonid fi shes has a saltwater or a freshwater origin has been discussed for decades. Anadromy appears to have evolved early among fi shes, as 90% of the 110 anadromous species identifi ed by McDowall (1988) are among either the most primitive living fi shes (e.g., lampreys and sturgeons) or the basal clupeocephalanteleosts. However, its presence among some neoteleosts (e.g., Gasterosteiformes, Gobioidei) suggests more than one independent origin of anadromy (Dodson et al. 2009). The evolutionary scenarios proposed by Gross (1987) were based on the assumption that the ancestral state of diadromous fi shes involves the reproductive environment. As such, catadromous fi shes (e.g., eels; Anguilla anguilla, A. rostrata, A. japonica and others) are derived from marine species that continue to exploit the ancestral reproductive environment. The ultimate derived state involves a completely freshwater life cycle. On the other hand, anadromous fi shes
Department of Aquatic Resources, Institute of Freshwater Research, Swedish University of Agricultural Sciences, Stångholmsvägen 2, SE-17893 Drottningholm, Sweden.