| Summary: | Restocking is one of the alternatives measures that have been widely used as a measure of remediation of ichthyologic biodiversity loss. To assess restocking efficiency, mass-marking provided the discrimination of restocked fish compared to wild fish. The use of fluorochromes recorded in the calcified structures such as otoliths has been used extensively to detect marked fish. However, reading mark on otolith requires the sacrifice of the fish. European eel recruitment collapsed down to 1% of 1980s levels. Within European eel management plan, restocked glass eel are marked with Alizarine Red S (ARS 150 ppm). The aim of our study was to implement a nonlethal ARS mark detection method using modern techniques of microscopy, imaging and fluorimetry. Batches of ARS marked and unmarked glass eels within a restocking protocol were collected before they were translocated. For marked and unmarked glass eels, ARS detection mark was assayed i) on glass eel fins with a binocular microscope, ii) on anesthetized glass eels using a fluorescence reflectance imager and iii) on a piece of caudal glass eel fins using fluorimeter. Among the three alternative methods tested, non-lethal ARS detection using fluorimeter appeared to be most efficient, the easiest method and the cheapest method. Overall, the present results provided a widely applicable, easy and non-lethal method to researchers and managers for detecting endangered marked fish.
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