Increments in otoliths and scales: How they relate to the age and early development of reared and wild larval and juvenile Pagrus auratus (Sparidae)

Abstract

The utility of otoliths and scales for age and growth studies on Northern and Southern Hemisphere forms of Pagrus auratus (<I00 days old) was investigated. A series of illustrations shows the developmental morphology of wild southern larvae at ages ranging from 0 to 40 days. Reared P. Auratus (of both forms) deposited daily increments in otoliths from or within 1 day of the time of hatching until the age of 40 days. Age-length relationships of wild P auratus (2.4-8.5 mm standard length, SL) from northern New Zealand (1985-86) were not significantly different among times and there was little variation in length at age among fish. In contrast, great variation in age-length relationships was found for reared larvae (5-30 days old). The data suggest that slow-growing fish may suffer high mortality rates in the wild. On the basis of age-length relationships of wild P. auratus, recommendations are made for appropriate sampling frequency in studies of larval abundance. Ctenoid scales formed at 8-9 mm SL in both forms of P. auratus. The number of increments in newly settled P. auratus (<60 days old) closely approximated the number of days since scale formation (i.e. t 2 5 circuli). This may provide a new method for estimation of the timing of a concurrent change in the behaviour of some fish larvae (e.g. a change in vertical distribution). Importantly, the number of circuli was correlated with the growth of juveniles, just as the spacing of circuli is in other species. Thus, circuli in scales potentially provide a history of individual growth in small fish after the formation of scales (to 100 days old) and an indication of the time since scales appeared.