Galaxias maculatus is a small diadromous fish found in Australia, New Zealand, South America and on some oceanic islands. Two hypotheses have been advanced to explain this widespread, disjunct distribution. McDowall promoted dispersal through the sea of salt-tolerant juveniles but Rosen and others claimed that the distribution reflected the break-up of Gondwana and subsequent drift of the southern continents. Allozyrne electrophoresis of muscle extracts of specimens of Galaxias maculatus from eastern and western Australia, New Zealand and Chile was used to test the hypothesis that populations of G. maculatus from the western Pacific and the eastern Pacific do not differ genetically. FST based on allele frequencies and genotypes was 0.14, suggesting only minor differentiation between eastern and western Pacific populations. Minor differentiation in allele frequency existed at some loci, but no fixation of alternative alleles has occurred. The populations examined appear to be part of the same gene pool, indicating that gene flow via dispersal through the sea occurs today. It is unlikely that South American and Australasian populations would be conspecific if they have exchanged no migrants since the break-up of Gondwana at the end of the Mesozoic.
Clearing and staining of Gambusia holbrooki facilitated
identification of juvenile fishes among the gut contents, and a feeding trial
with captive Gambusia allowed assessment of gut transit
time and degradation of melanotaeniid larvae. Regurgitated fishes and eggs in
fixative solutions were also investigated. These techniques, extending to 12 h
the post-feeding interval in which fishes may be found and differentiated
among Gambusia gut contents, were tested on 631
wild-caught Gambusia collected in eastern Australia; an
ingested native fish could be identified in the gut of 18
Gambusia, and a cannibalized fish in the gut of three.
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