Optimising chemical marking techniques for Australian bass, Macquaria novemaculeata, fry and fingerlings prior to restocking

Many stocking programs are performed without any subsequent assessments to determine the survival of the stocked fish, often due to the difficulties in distinguishing stocked from wild fish. A series of optimisation trials were undertaken to determine the suitability of calcein (2,4-bis-[N,N'-di(carbomethyl)-aminomethyl]fluorescein) for chemically marking hatchery-reared Australian bass, Macquaria novemaculeata (Steindachner), fry and fingerlings. The technique was optimised by trialling immersion times for salt (2.5 or 5 min), calcein concentrations (0.5 or 1%) and calcein immersion times (5 or 10 min). A general-purpose modulated probe fluorometer was used as a non-lethal detection method to establish mark retention and distinguish between calcein-marked and unmarked fish. Five minutes of saline immersion, followed by 10 min of calcein immersion at a calcein concentration of 1% was the optimal marking method. Growth and survival of fish was not affected as a result of any of the calcein-marking methods. It is therefore effective to calcein-mark Australian bass fry and fingerlings before stocking and to non-lethally detect marked individuals using a field-portable meter to assist in the assessment of stocking programs. Findings from this study may also reflect the potential use of calcein to chemically mark fry and fingerlings of other fish species.