ABSTRACT
Diadromous fi shes differ from other types of fi shes because they migrate between freshwater or estuarine habitats and the marine environment at specifi c times in their lives. There are only about 250 species of diadromous fi shes compared to the likely more than 30,000 or more species of purely freshwater, estuarine or marine fi shes (McDowall 1988, 1997; Nelson 2006), so they are a unique subset of the world’s fi shes. The categories of diadromous fi shes have been defi ned based on which life history stages use the marine and freshwater habitats and for what purpose (Myers 1949; McDowall 1988, 1997). Catadromy is a diadromous life history with the fi sh using the marine environment for reproduction and larval growth and using freshwater for juvenile growth. Or more specifi cally, McDowall (1997) provided a detailed defi nition of catadromy as: “Diadromous fi shes in which most feeding and growth are in fresh water prior to migration of fully grown, adult fi sh to sea to reproduce; there is either no subsequent feeding at sea, or any feeding is accompanied by little somatic growth; the principal feeding and growing biome (freshwater) differs from the reproductive biome (the sea).” This defi nition however seems to have expanded somewhat to include estuaries as a separate biome, which would then include fi sh that migrate from freshwater to estuarine habitats to reproduce, or from estuarine to marine habitats to reproduce, with the juvenile growth biome being either freshwater or estuarine habitats. Further complicating this issue is that many seemingly catadromous species have plasticity in their life history patterns especially in terms of how much they may use the pure freshwater environment (Tsukamoto and Arai 2001; Daverat et al. 2006, 2012; Walther et al. 2011).
