The species problem in freshwater fishes and the taxonomy of diadromous and lacustrine populations ofGalaxias maculatus(Jenyns)

Abstract

THE species problem in freshwater fishes, in which allopatry is the norm, is discussed. Biological species criteria break down because of the general occurrence of allopatry, and the implications for the taxonomy of freshwater fishes are explored. Essentially morphological criteria must be used, but their use must be subject to careful scrutiny, and patterns of variation must be studied.Galaxias maculatus (Jenyns) is shown to occur in Australia, New Zealand, Chatham Islands, Chile, Tierra del Fuego, and Falkland Islands in the typical diadromous form. Subspecies are not recognised. Landlocked or freshwater-limited populations occur through much of the range of the species, and in these populations vertebral number is reduced to about 55, from about 62 in diadromous stocks. These populations are not given separate taxonomic recognition, variation in vertebral number being regarded as related to the transition from a diadromous to a wholly freshwater life history; G. usitatus McDowall and G. parrishi

Mitochondrial and allozyme genetics of two Tasmanian galaxiids (Galaxias auratus and G. tanycephalus, Pisces: Galaxiidae) with restricted lacustrine distributions

“…Speciation following landlocking of diadromous populations of G. truttaceus is the most tenable explanation of the evolution of G. auratus and G. tanycephalu.s, given their biogeography and phenotypic relationship to G. truttaceus and the tendency of G. truttaceus to intrude gradually into inland waters (McDowall, 1972;Andrews, 1976;Fulton, 1978). The formation of lacustrine populations of G. truttaceus via landlocking, and its genetic implications, have previously been studied by Ovenden & White (1990).…”

“…The derivation of landlocked, entirely freshwater species from inland invading diadromous species is thought to be a major speciating force in the genus (McDowall, 1972;Andrews, 1976). Accordingly, G. auratus and G. tanycephalus are assumed to be landlocked derivatives of the ubiquitous G. truttaceus (Fulton, 1978;Humphries, 1989).…”

Distribution and conservation status of the dwarf inangaGalaxias gracilis(Teleostei: Galaxiidae) an endemic fish of Northland dune lakes

“…McDowall (1972) later identified the galaxiids in Lake Waiparera as landlocked G. maculatus but, although we suspected that the galaxiids in Lake Ngatu would also be landlocked G. maculatus, we could not discount the possibility that they might be G. gracilis. Unidentified galaxiids were also reputed to be present in other, more northerly lakes by Department of Conservation staff.…”

“…Land-locked populations of Galaxias maculatus (Jenyns) and Galaxias fasciatus Gray were later found in some of the more southerly lakes surveyed (McDowall 1972;Schipper 1979), but the galaxiids in lakes on the North Kaipara Head and further north remained unidentified.…”

The Tarndale bully,Gobiomorphus alpinusStokell (Pisces: Eleotridae) revisited and redescribed

“…Criteria of species recognition based on biological species definitions (Mayr, 1969) pose problems for freshwater fishes, because there is often widespread and longterm retention of allopatry in derived populations (McDowall, 1972). In these circumstances there is no basis for deciding taxonomic status on criteria of reproductive isolation, and it becomes a question of subjective judgement.…”