Golden perch, Macquaria ambigua, from the Murray-Darling Basin were aged by using transverse thin sections of their sagittal otoliths. Samples from 889 fish were obtained from riverine and lacustrine habitats and from wild and stocked populations. Error in the precision of age estimates (calculated as the mean percentage error of the independent age estimates of four readers) was 5.6% (3.9% after allowing for discrepancies in relation to the annual mark on the edge of the otolith). Validation was accomplished by using a combination of analysis of the progression of modes in length-frequency distributions, qualitative and quantitative marginal-increment analysis, and analysis of age estimates of fish from populations with a known stocking history. The technique was validated for fish up to 8 years of age (455-545 mm total length, 1695-3988 g total weight), and the greatest recorded age was 16 years (530-600 mm total length, 2607-4050 g total weight). Annual marks become visible in otolith sections in most fish of all ages in October, and 1 October was designated as the birth date. A description of our method of reading sections of golden perch otoliths, including recognition of false annual marks, is given. Otolith length, width and thickness increased linearly with fish length and with loglo(fish age), whereas otolith weight increased linearly with fish age and exponentially with fish length. The continuous growth of the otoliths and the consistency in the appearance of annual marks support the accuracy of estimates up to the maximum recorded age. The mean length-at-age and the parameters of the length-weight relationship were estimated. The von Bertalanffy growth parameters were also estimated (L∞ =507 mm, to=0.420 years, K=0.454). No significant differences were found in growth rates or length-weight relationships between males and females. However, growth (particularly in weight) was highly variable among sites and years, and slow-growing 5-year-olds may be shorter than fastgrowing 1-year-olds. Ages were estimated for a sample of 86 golden perch caught between 1949 and 1951 but a comparison of growth rates between these and more recent collections was inconclusive.

Transverse thin sections (0.5 mm thick) of sagittal otoliths from 290 Murray cod up to 1400 mm in total length and 47.3 kg in weight were used to establish the age and growth of cod in the lower Murray-Darling Basin, including comparisons of recent (1986-91) and past (1949-51) growth rates and growth in different waters. The maximum estimated age was 48 years. Quantitative and qualitative analysis of the seasonal changes in otolith marginal increments showed that annuli in fish of all ages were laid down each spring, and 1 October was assigned as the birthday. The thin-sectioning method was validated by comparing age estimates for 55 Murray cod from Lake Charlegrark (age 0-21 years), which had been validated by using burnt and polished half-otoliths. The new method had an accuracy of 96.4% and it offers major advantages in ease of preparation, reading, and batch-handling of large numbers of otoliths. The precision of the method, estimated as an average error for four readers, was 5.4% (3.0% after ignoring discrepancies in relation to annuli on otolith edges). There was a linear relationship between otolith weight and fish age and an exponential relationship between otolith weight and fish length. Both otolith length and otolith width reached an asymptote at about 15 years, when fish length also approached its maximum. However, otolith thickness continued to increase throughout the life of the fish and, after about 15 years, contributed most to the increase in otolith weight. This confirmed that otoliths continued to grow in thickness and that annuli were laid down throughout life, and that cod could be aged reliably to the maximum age. The annulus pattern is very clear and distinct, and the reading techniques are fully described, including recognition of 'larval' and 'false' rings. Various differences were found in the growth rates, and the length-weight relationships for males and females, for cod caught in 1986-91 and those caught in 1949-51, and various subpopulations are discussed. The von Bertalanffy growth parameters (all individuals combined) were estimated at L∞ = 1202 mm, k=0.108 and t0= -0.832. The availability of a reliable ageing method provides the first opportunity to determine year of birth and thus to examine the age structure of populations and to effectively manage cod populations that have declined in abundance.

No abstract

John Edwards Holbrook (1794–1871), zoologist and medical doctor, residing in Charleston, South Carolina, apparently sent eight colour plates of North American fishes to the museum in Paris because they were found in the Bibliothèque centrale, Muséum national d' Histoire naturelle, with known Holbrook material, most significantly a copy of his 1855 edition of the Ichthyology of South Carolina. Herein, I comment upon the illustrations of the 16 fishes rendered in those plates.