Abstract. Natural levels of 21°pb:226Ra in otoliths of orange roughy, Hoplostethus atlanticus, from south-east Australian waters, were measured to determine fish ages radiometrically. Up to maturity, radiometric age estimates were consistent with a single constant otolith growth rate. Radiometric ages for juveniles were comparable with, but greater than, those obtained in a recent, validated New Zealand study which employed counts of annuli on the surface of otoliths. Beyond maturity, radiometric ages were obtained by modelling with an otolith growth rate set at 45% of the juvenile rate. Radiometric ageing confirms that orange roughy is very slow-growing, with an age at maturity (32 cm standard length, SL) of ,-~ 32 yr, and is very long-lived, with fish 38 to 40 cm being 77 to 149 yr old. These results have important implications for the management of the fishery.

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Ages of orange roughy (Hoplostethus atlanticus) determined by two methods (counting annuli on the surface of whole and in longitudinally sectioned otoliths) were similar up to maturity. Beyond maturity, age estimates from sectioned otoliths exceeded those from whole otoliths. Maximum recorded age was 125 years for an individual 41 cm standard length (SL), and age at maturity was estimated to be 25 years (30–32 cm SL). These are consistent with ages estimated previously by radiometric methods. Results demonstrated a two-stage linear relationship between otolith weight and age that confirmed the two-stage otolith mass growth model previously used in radiometric ageing. However, in the radiometric analyses the reduction in otolith growth was arbitrarily estimated at 45% of the immature rate whereas annuli data demonstrated a reduction after maturity to 62% of the immature rate. The new estimates of otolith mass growth rate were incorporated into the radiometric data and ages recalculated, which reduced age estimates for 38–40 cm SL fish from 77–149 to 59–101 years. The radiometric data were also recalculated using only the percentage reduction in otolith growth after maturity, giving the radiometric age of 125 ± 9 years for the oldest fish.

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Annual p roduction estimates were calculated for Tenagomysis tasmaniae, Anisomysis mixta australis and Paramesop odop sis rufa using the size-frequency and Petrovich methods . Annual p roduction for T tasmaniae was more than twice that for P rufa and A . mixta australis. The P :B ratio was however, higher for A . mixta australis than T tasmaniae and P rufa . The P :B values for the three sp ecies are among the highest ratios rep orted for mysids .