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ASFB Home > The effects of spatial and temporal factors on the abundance of seven key finfish species along south-western Australia.
PRESENTATION 1: Age and Growth of the Endangered Eastern Freshwater Cod (Maccullochella ikei) in the Mann-Nymboida Rivers of Northern NSW.
GRAFTON, AUSTRALIA
THEME: ASFB
The eastern freshwater cod (Maccullochella ikei) is one of Australia's most endangered freshwater fish species, restricted to one small catchment in Northern New South Wales. However, despite the conservation status of the species little is known of their biology. The aim of this study was to determine the age, growth and forage preference of M. ikei in the Mann-Nymboida River systems. To determine age-at-length of M. ikei; otoliths, operculum bones and dorsal spines were gathered from archival collections, supplemented by 16 samples collected throughout 2001. Operculum bones and dorsal spines were found to have no consistent annuli present. Age was determined for 52 sectioned otolith samples. Relationships were established between age and total length of fish, and otolith weight, width and diameter. Cod were aged from one year to a maximum of 13+ years. Edge increment analysis was used to validate age estimates. High variability was apparent in length at age, particularly in older fish. Back-calculated mean length at age estimates were used to determine von Bertalanffy growth constants. The von Bertalanffy growth equation for M. ikei was Lt = 864.05{1-exp[-0.1677(t+0.26138)]}. Length-weight relationships of cod were established from 56 samples, with growth found to be close to isometric (7.62x10-6xL3.0949). Crustaceans and molluscs were the most prevalent food groups in stomachs of 16 cod sacrificed for the age and growth study. During winter M. ikei appears to be a foraging species rather than piscivorous as previously assumed. The results of this study suggest that M. ikei is unique from other closely related cod species and consequently requires management strategies that consider this individuality. Recommendations for further research include the establishment of databases to collate age length, weight and diet from opportunistic samples.
