Ovarian biopsy: a non-terminal method to determine reproductive status in giant kokopu, Galaxias argenteus (Gmelin 1789)

Abstract

AIM: To establish a method of gonad biopsy for ovarian tissue collection in the declining giant kokopu Galaxias argenteus (Gmelin 1789) as an alternative to lethal sampling in order to understand the species' reproductive biology.

METHODS: Six female giant kokopu weighing between 200 and 350 g were caught from the wild in early December of 2009 and transferred to a holding facility (Department of Zoology, University of Otago, Dunedin) where they were kept under a simulated natural photo-thermal regime for 10 months. Fish were repeatedly biopsied for ovarian tissue at near-monthly intervals (mean number of days between biopsies = 33) until ovulation.

RESULTS AND CONCLUSIONS: Ovarian samples were successfully collected from giant kokopu by biopsy for use in downstream analyses. Among a total of 23 biopsy events, a single death occurred when a two-layered suturing approach was used, highlighting the value of this method for study of the reproductive biology of valuable fish.

CLINICAL RELEVANCE: This biopsy method may have implications for veterinary research on fish physiology, pathology, conservation and development, when repeated tissue samples need to be collected over a prolonged period of time or for general surgical manipulations on fish when accessing the coelom. Furthermore, this approach allows the implementation of a more powerful experimental design, as repeated measures reduces the variability of estimates due to the removal of inherent stage differences among individuals.

Keywords:

• Kokopu
• surgery
• conservation
• biopsy
• fish
• suture
• gonad
• ovary
• whitebait

Acknowledgements

The authors would like to thank R and G Munro of Mokotua for access to their property to capture fish. We are also grateful to Associate Professor Greg Jones, University of Otago and Gardens Veterinary, Dunedin for guidance with the surgical procedures and for proof-reading of this manuscript. Subsidised surgical equipment and aquarium products were kindly supplied by Gardens Veterinary and Pet Planet Ltd, Dunedin. This study was funded by the Foundation for Research, Science and Technology TeTipuPūutaiao Fellowship (contract number: UOOX0910). Funding for publication was also received from the University of Otago Postgraduate Publishing Bursary. The authors also wish to thank the anonymous referees for their constructive feedback.