New Zealand Journal of Marine and Freshwater Research abstracts
First record of mosquitofish, Gambusia holbrooki, in Tasmania,
Australia: stock structure and reproductive biology
John P. Keane
Francisco J. Neira
Faculty of Fisheries and Marine Environment
Australian Maritime College
P.O. Box 21
Beaconsfield
TAS 7270, Australia
email: f.neira@fme.amc.edu.au
Abstract The first population of mosquitofish, Gambusia
holbrooki, was discovered in a wetland area of the upper Tamar Estuary,
northern Tasmania, Australia, in November 2000. We report aspects of the
structure and reproductive biology of this population, based on 1567 fish
collected between August 2001 and January 2002. Females dominated most catches.
Maximum lengths were 48.9 and 23.6 mm standard length (SL) for females and
males, respectively. Growth of the over-wintered cohort was evident from
October, when temperatures reached >19°C; growth rates in the young-of-season
cohort from length frequency plots were 0.38 mm/day for females and 0.19
mm/day for males. Estimated SL at 50% maturity for females (25.0 mm) and
males (17.4 mm) were attained within 7 weeks of birth. Developing embryos
were present from mid October and offspring from mid November; average number
of stage III embryos was 55.5 (3–144). Given their rapid reproductive turnover
(c. 34-day gestation period) and resilience to broad environmental conditions,
it is likely that this exotic pest will spread to other Tasmanian localities,
as it has already been discovered in areas near the wetlands since the completion
of this study.
Keywords mosquitofish; reproductive biology; Gambusia
holbrooki; exotic pest; Tamar Estuary; Tasmania
M04053; Online publication date 24 November 2004 Received 1 March 2004;
accepted 28 May 2004
New Zealand Journal of Marine and Freshwater Research, 2004, Vol. 38:
857–867
0028–8330/04/3805–0857 © The Royal Society of New Zealand 2004
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