LIPOFUSCIN AGE-PIGMENT ACCUMULATION IN THE BRAINS OF AGING FIELD-REARED AND LABORATORY-REARED CRAYFISH CHERAX-QUADRICARINATUS (VONMARTENS) (DECAPODA, PARASTACIDAE)

Fluorescence microscopy and image analysis were used to quantify lipofuscin in the base of the olfactory nuclei of 10 laboratory- and 17 field-reared freshwater crayfish, Cherax quadricarinatus, 2.4-2.5 years of age. These data, with those from earlier studies, indicated that there was probably a slowing of lipofuscin accumulation and metabolic rate in large/old individuals between 1 and 2.4 years. The ranges of carapace length and body weight in the 2.4-yr laboratory group fell entirely within those of the 1-yr group. It was impossible to accurately distinguish individual crayfish from these age groups using traditional size criteria. Conversely, there was no overlap in the brain lipofuscin contents of individuals from the two age classes, enabling 100% differentiation on this criterion. Although increasing variation in lipofuscin concentrations and slowing of the accumulation rate with increasing age would lead to widening confidence intervals of age predictions for older individuals, the present results again demonstrate that, at least in these laboratory reared crayfish, lipofuscin is a much better predictor of age than conventionally used size indices. Despite a wide range of ambient water temperatures (7-33-degrees-C, mean 19-degrees-C), the variance of lipofuscin concentrations in the 2.5-yr-old field-grown crayfish was not significantly different from that of similarly aged individuals reared under constant laboratory conditions, suggesting that individuals in the population were relatively cohesive in their response to varying temperatures and that confidence levels for age determinations of field animals might be of the same order as those obtained for laboratory subjects. The results of the present study are further incentive for continuing the evaluation of lipofuscin as an index of crustacean age.