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A Cost-Effective Method of Preparing Larval Fish Otoliths for Reading using Enzyme Digestion and Staining.

Bridget Green, Sue M Reilly and Mark I McCormick

James Cook University, DOUGLAS, AUSTRALIA

THEME: ASFB (Poster)

We developed a fast and cost-effective method for examining otoliths in fish larvae whereby the otolith remains in situ. Whole fish were enzyme-cleared using a laundry pre-soak and then stained using the Von Kossa silver staining method for calcium. The otolith nucleus, daily rings and the otolith edge were all clearly visible, suitable for a variety of age and growth analyses. The total hands on time for required to process these otoliths was approximately three minutes, and 10's-100's of samples can be processed simultaneously. Examining otoliths in tropical reef fish larvae is traditionally a very time-consuming and difficult operation. The method presented here avoids the time-consuming process of removing and grinding the otolith, thus circumventing the likelihood of breaking or losing valuable samples. This method has been successful preliminarily on three species of pomacentrids, and extensively on one species. The reduction in labour of this method to produce clear daily rings in the otolith lends itself to broad use in fisheries monitoring where large quantities of otoliths need to be examined in a cost- and time- efficient manner.