Glycerol impregnation of a formaldehyde fixed Bump-head Sunfish Mola alexandrini

A Bump-head Sunfish Mola alexandrini washed ashore in south-western Australia and was provided to the Western Australian Museum for exhibition. However, using traditional museum practices, such a large specimen would require a large volume of ethanol, which provides an unacceptable public risk in an exhibition space. The low risk glycerol was chosen as a storage medium. The specimen was initially fixed in a 10 v/v% formaldehyde solution and soaked in fresh water to remove residual formalin before commencing glycerol impregnation. Over a period of several years, glycerol impregnation was achieved by step-wise increases at 30%, 40%, 49% and 59% glycerol. Biodegradation was inhibited with Kathon CG biocide. The impregnation process was monitored with a digital densitometer, which confirmed the process was controlled by diffusion through the spaces surrounding denticles and the concentration of the impregnating solution and was dependent on the logarithm of time. This method is a viable and safe alternative to the storage of natural history specimens when ethanol is not an option, and delivers measurable improvements to the colour and flexibility of specimens.