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Advances in the aquatic sciences

Estuarine geomorphology and low salinity requirement for fertilisation influence spawning site location in the diadromous fish, Galaxias maculatus

Andy Hicks A C , Nicole C. Barbee A D , Stephen E. Swearer A and Barbara J. Downes B
+ Author Affiliations
- Author Affiliations

A Department of Zoology, University of Melbourne, Vic. 3010, Australia.

B Department of Resource Management and Geography, University of Melbourne, Vic. 3010, Australia.

C Present address: Department of Zoology, University of Otago, PO Box 56, Dunedin, New Zealand.

D Corresponding author. Email:

Marine and Freshwater Research 61(11) 1252-1258
Submitted: 19 January 2010  Accepted: 21 May 2010   Published: 16 November 2010


In habitats such as estuaries, which are characterised by large and fluctuating gradients in abiotic variables, finding appropriate habitat for successful spawning and egg development can be critical to a species’ survival. We explored how salinity requirements for successful fertilisation may govern the distribution of estuarine spawning habitat for the diadromous fish, Galaxias maculatus, which spawns in inundated vegetation on estuary banks during spring tides. Artificial fertilisation experiments confirmed that successful fertilisation only occurs at low salinities (<20). Thus, we predicted that egg distributions would depend upon the extent of low-salinity surface waters in an estuary. Using estuary geomorphology classification schemes, which classify estuaries by physical and chemical characteristics such as their salinity dynamics, we hypothesised that stratified estuaries would provide a greater extent of low salinity surface water than well-mixed estuaries. This prediction was supported by surveys of egg distributions in five estuaries in Victoria, Australia. Eggs were distributed over a greater proportion of ‘stratified’ v. ‘mixed’ estuary types. We suggest that combining knowledge of the spawning requirements of a species and physical properties of the habitat, such as those encapsulated in estuary geomorphic classification schemes, can greatly facilitate efforts to identify critical habitats and thus aid in species management and conservation.

Additional keywords: estuary geomorphology, fertilisation success, galaxiid, geomorphic classification, salt wedge.


We thank John Morrongiello and Dave Semmens for assistance with fieldwork and constructive comments on the manuscript. We also thank Scott Hardie, Prof. Andrew Boulton, and an anonymous referee for helpful and constructive reviews. This research was conducted under University of Melbourne Animal Ethics Committee approval #03188 and DPI Fisheries Permit #RP700. Funding was provided by a grant from the Australian Research Council to S.E.S. and B.J.D., and by the Department of Zoology at the University of Melbourne.


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