New insights into detecting alizarin from autofluorescence in marked glass eels.

Alizarin detection in fish fins is extensively employed because it is easy to use. However, in eels, the eelGFP fluorescent protein may impede the detection of the fluorescent markers in the eel tissues. The study tests the effectiveness of three of the most up-to-date alizarin-detecting technologies on the living body and fins of European glass eels (Anguilla anguilla L.). The findings demonstrated that the control group had a high autofluorescence at alizarin and eelGFP maxima bands. With fluorescence reflectance imaging (FRI), the eel living body autofluorescence impeded the detection of the marked eels. In contrast with experimental excitation-emission-matrix (EEM) fluorescence analyses, 99% of the marked eels were correctly assigned to their group from fluorescence analyses of their fin cellular contents. With epifluorometry (EPI), 100% of the marked eels were detected with the caudal fin tips when excited at 450-490 nm wavelengths due to a weaker autofluorescence signal. EEM and FRI assays unveiled an average fluorescence quenching 60% and 44% of the marked group respectively, in the alizarin and eelGFP maxima bands. The fluorescence quenching observed is discussed. Results will benefit experimental design by examining autofluorescence effects on mark detection and the development of non-invasive detection methods in this critically endangered species.

Trends of a bitterling (Rhodeus sericeus) population in a man-made ditch network.

This study describes the trends of a bitterling population in the Bourgneuf Marsh in relation to human activities. Although there were no bitterling during the period 1987-91, the species rapidly colonized the ditch network sampled (density reaching 61.7 +/- 47.0 individuals/100 m2 and frequency of occurrence around 70-75%) during a 5-year period (1997-2001). Clearance operations probably favoured the expansion of this vulnerable fish species because of positive associations of bitterling with large and deep ditches that had been cleared in the last 2-3 years and characterized by a small cover of submerged plants. Management recommendations are discussed for conserving the bitterling population.