Estimating age and growth in long-lived temperate freshwater crayfish using lipofuscin

1. In ecological studies on freshwater crayfish, determination of basic population parameters is often complicated by the lack of a suitable age estimation method. 2. Previously, lipofuscin age pigment in the olfactory lobe cell masses (OLCM) of short-lived tropical crayfish has been used for accurate age determination. Here we present the first test of this method on a longer-lived, temperate species, the signal crayfish, Pacifastacus leniusculus. 3. Confocal fluorescence microscopy and image analysis of histological sections were used to quantify OLCM lipofuscin in a reference sample of Swedish P, leniusculus from several known year-classes, reared under naturally variable temperature conditions. Lipofuscin concentration was linearly associated with age (r(2) = 92.4%) and produced much more accurate age estimates than conventional body size-based procedures. 4. A model derived from the crayfish of known-age was used to estimate the ages of wild P. leniusculus from an English stream. The relationship between lipofuscin-estimated age and carapace length suggested relatively slow growth in this wild population, consistent with a high population density and severe competition. The analysis also extended the known longevity of P, leniusculus to approximately 16 years. 5. The lipofuscin method for determining age and growth may be widely applicable to freshwater crayfish with probable further potential both within and outside the Crustacea.