Nucleic acid content as a potential growth rate estimator of Antarctic krill; results from field-caught krill from the indian sector of the southern ocean

Abstract

Nucleic acid contents of tissue were determined from field-caught Antarctic krill to determine whether they could be used as an alternative estimator of individual growth rates which can currently only be obtained by labour intensive on-board incubations. Krill from contrasting growth regimes from early and late summer exhibited differences in RNA-based indices. There was a significant correlation between the independently measured individual growth rates and the RNA : DNA ratio and also the RNA concentration of krill tissue, although the strength of the relationship was only modest. DNA concentration, on average, was relatively constant, irrespective of the growth rates. The moult stage did not appear to have a significant effect on the nucleic acid contents of tissue. Overall, the amount of both nucleic acids varied considerably between individuals. Nucleic acid-based indicators may provide information concerning the recent growth and nutritional status of krill and further experimentation under controlled conditions is warranted. They are, however, reasonably costly and time-consuming measurements.

Keywords:

• Antarctic krill
• RNA : DNA
• Growth rate
• Nutritional status
• Moult

Acknowledgements

We thank Andrew McMinn, Robin Ross, Angus Atkinson, Fred Buchholz and an anonymous reviewer for their useful comments. The first author gratefully acknowledges Overseas Postgraduate Research Scholarship from the Australian government, and a partial stipend scholarship from Australian Antarctic Division.