Age of Australian bass, Macquaria novemaculeata (Perciformes : Percichthyidae), in the Sydney Basin

Abstract

The age of M. novemaculeata from the Hawkesbury River and other streams in the Sydney Basin, New South Wales, was determined by using otoliths. Annuli were counted after simple sectioning of otoliths and intensification of the growth-check pattern by a two-stage burning technique. Age determinations were validated by the use of fish of known age; an error of + 1 year occurred in 17% of determinations. Ages of older fish (14+ to 18+ years) were not overestimated by more than 2-4 years, if at all. Progression of year-classes, and the annual nature of growth-check formation, further validated age determinations. Scale-reading seriously underestimated the age of bass.

M. novemaculeata is a long-lived species. The oldest fish was 22+ years, and the mean age of the sample (n = 607) was 4.9 years. There are significant differences in longevity between the sexes; fewer males reach the older age-groups. About 10% of juvenlle fish deposited a growth-check in their otoliths during their upstream recruitment migration. The frequency of this 'migration check' was increased to 20% by capture and relocation of juveniles to isolated waters. A procedure was designed to identify migration checks in wild fish.