Background and review of ageing orange roughy (Hoplostethus atlanticus, Trachichthyidae) from New Zealand and elsewhere

Abstract

Studies on New Zealand orange roughy (Hoplostethus atlanticus) otoliths, and of orange roughy ageing conducted in New Zealand and elsewhere are described. Ageing studies have concentrated on three aspects: the interpretation of daily growth increments, the interpretation of annual growth increments, and radiometric analyses. All the methods suffer from problems relating to validation. Daily growth zones have not been validated, annual zones have been validated for juvenile fish only, and assumptions necessary for the application of radio‐metric techniques may be flawed. However, the weight of current evidence indicates that orange roughy are a slow‐growing, long‐lived species. A review of otolith morphology and microstructure studies, and a summary of the productivity parameters used in stock assessments of orange roughy, are also presented. Standard protocols used to prepare and interpret otoliths in current investigations are described. This review highlights the complexities of ageing long‐lived, deepwater fish, and stresses the importance of obtaining accurate productivity parameters for stock assessment. The key area for future research is the age validation of post‐juvenile fish, which should lead to the development of an accurate ageing technique.