Migration history and stock structure of two putatively diadromous teleost fishes, as determined by genetic and otolith chemistry analyses

Abstract

Migratory life cycles and population structure of 2 putatively diadromous Australian fishes were examined using otolith chemistry (87Sr/86Sr) and genetics (microsatellites and mitochondrial deoxyribonucleic acid [mtDNA]). Australian whitebait (Lovettia sealii) is widely considered to be one of only a few anadromous fish species in the southern hemisphere. The congolli or tupong (Pseudaphritis urvillii) is reported to undertake an unusual form of sexually segregated catadromous migration, where females switch habitats between marine and freshwater, while males remain in marine or estuarine environments. Sr-isotope profiles of L. sealii showed this species does not move into fully freshwater habitats during its life cycle, suggesting it should be considered semi-anadromous or estuarine-dependent, rather than truly anadromous. This life-history strategy is unique among the Galaxiidae. Lovettia sealii is regionally divided into at least 3 well differentiated genetic stocks: northern and southern Tasmanian coasts and mainland Australia. Sr-isotope profiles of P. urvillii showed that females are catadromous, with the early life history spent in the marine environment and a single migratory transition from marine to freshwater occurring at an early point in the life history. Lack of bidirectional adult migration between freshwater and the sea suggests that female P. urvillii are semelparous, returning to the marine habitat to mate with resident males after an extended period of freshwater residence. Pseudaphritis exhibit weak genetic structure across their mainland range. An isolation-by-distance relationship describes the genetic structure of this species, a pattern it shares with several other nearshore-restricted catadromous fishes.