Background/Aims:
Migrations are core to the life history of many species but are energetically expensive and risky. Triggers for migration are encoded into an individual’s life history and often respond to environmental cues but are still poorly understood for many species. In anticipation for their one-way migration to distant marine spawning grounds, freshwater anguillid eels undergo a final metamorphosis, called ‘silvering’, by which freshwater-residing ‘yellow’ eels cease feeding and begin to change into sexually mature, migratory ‘silver’ eels. However, we still do not know what initiates silvering with some eels silvering as early as 5 years of age, and others as late as 30 years. We aim to evaluate a suite of morphological and physiological traits as possible triggers of the silvering process.
Methods:
Specifically, we measured age, body size mass, condition and lipid content of both yellow and silver short fin eels, Anguilla australis. We collected A.australis from Boonwurrung Country during the eel autumnal migration season, known traditionally as Iuk, using a combination of fyke nets and electrofishing. In the lab, we assessed migration status (using Gonadal somatic index), recorded morphological measurements (Gonad weight, Length, Weight), estimated age and early life growth rate using otolith analysis, synthesised bulk lipids from tissue samples (muscle and liver) of yellow and silver eels.
Conclusion:
Collectively, these findings provide a baseline understanding of the morphological differences between feeding and migratory phases of anguillid eels in Southeast Australia. Our understanding of basic eel biology and their life history is essential for mitigating both natural and anthropogenic threats within growth habitat and along migration routes.