MORE ACCURATE CHRONOLOGICAL AGE-DETERMINATION OF CRUSTACEANS FROM FIELD SITUATIONS USING THE PHYSIOLOGICAL AGE MARKER, LIPOFUSCIN

A captive population of Australian red-claw crayfish, Cherax quadricar inatus, of known age was used for the study. Lipofuscin concentration in the left olfactory lobe cell mass of the brain was measured using i mage analysis of fluorescence micrographs. Age predictions based on li pofuscin concentration were more accurate and had narrower 95% confide nce limits than those derived from the more conventional body size and weight predictors for all age groups tested (180, 300, 420, 780 d). O verall, use of lipofuscin concentration produced a significantly lower (p < 0.001) mean age-prediction error (16.65%)than use of carapace le ngth or body weight (32.45 and 32.3%, respectively). Carapace length w as of little value for prediction of the age of older individuals. Mat hematical models defining the relationships between temperature, age a nd lipofuscin accumulation were derived from laboratory-reared individ uals. These models did not describe adequately the course of lipofusci n accumulation in crayfish from the field over the whole lifespan. Fie ld data from three ''known'' year-classes were used to generate simula ted size-frequency and lipofuscin concentration-frequency histograms. Year-classes in the lipofuscin concentration frequency-histogram were much more easily distinguished than in the size-frequency histogram. U nder field conditions, lipofuscin concentration was a better predictor of chronological age than conventional morphometric measures.