Reproductive phenology of river and lake populations of freshwater mussels (Unionida: Hyriidae) in the River Murray

ABSTRACT

Gonadal cycles are described for Alathyria jacksoni and Velesunio ambiguus from the River Murray at Overland Corner (near Lock 3) and for V. ambiguus at Point Sturt, Lake Alexandrina. The study included periods of low flow (1982), minor flooding (1983) and intermediate flow (1986). In males, gametogenesis continued year-round with fertilisation in late winter. Female A. jacksoni brooded embryos in spring and released glochidia during spring and summer, whereas in female V. ambiguus, glochidia were present most of the year, with peak releases in spring and summer. In both species, the proportions of actively reproducing individuals varied. In the Murray, populations were influenced by variations in discharge. At Point Sturt, gonadal cycles in V. ambiguus were irregular, influenced by variable lake levels. Although both species are essentially gonochoristic, there were hermaphrodites in river and lake populations, and a female bias in the population at Point Sturt. Infections by parasitic trematodes at Point Sturt were rare, but occurred in 10% of A. jacksoni and 35% of V. ambiguus at Overland Corner. The river populations were also affected by gill damage due to unionicolid mites. The disparities in infections between river and lake mussels are unexplained, but did affect their reproductive activity.

KEYWORDS:

• Bivalvia
• doubly uniparental inheritance
• hermaphrodites
• gametogenesis
• life history
• Murray–Darling Basin
• Trematoda
• Unionicolidae

Acknowledgements

The author is greatly indebted to Sandi Poland, who assisted in field and laboratory work in 1986, and to Jane Moller, who gathered data in 1981–83. Other valuable assistance was rendered at different times by Julie Francis, Hugh Jones, Vicki Laslett, Lance Lloyd and Fran Sheldon, and by the late Shirley Balla and Jim Puckridge. Maria Byrne, Hugh Jones and Michael Klunzinger kindly contributed unpublished data, and Dr Klunzinger made helpful comments on a draft. This paper was submitted shortly before the author’s death and we are grateful to the two reviewers, Prof. Art Bogan and Prof. Maria Byrne for reviewing the manuscript. The final alterations to the text were undertaken by Hugh Jones and Fran Sheldon.

Disclosure Statement

No potential conflict of interest was reported by the author.