0 avis
Field survey of externally detected fluorescence on calcein marked brown trout (Salmo trutta L.) fingerlings
Archive ouverte
Edité par CCSD -
National audience. Brown trout population management requires mass-marking experiments in order to assess stocking efficiency. Many fluorescent markers may be used, but recent studies revealed a great interest for calcein. This dye combines with calcium, and thus fixes not only in internal skeleton but also in other bony tissues like fin rays and scales. Therefore, an external detection in the field becomes possible using either scale samples, or a portable detector (SE-MARK, Western Chemical Company). Fish may be kept alive and then released after analysis. Although several studies have already focused on improving a protocol in fish-farm, published data regarding field tests are actually lacking. Therefore, we aimed at testing the methodology defined by Mohler (2003) for Brown trout, through marking experiments conducted for the first time in situ. The objectives were: 1/ to assess whether calcein could be externally detected in the field after 1 or even 2 years; 2/ to compare the results between different streams and reaches; and 3/ if differences between sites are noticed, to provide hypothesis explaining these variations. Tests in rivers were carried out in Switzerland in 4 small streams from the Rhone and Rhine basins. Fingerlings were marked either in early or late summer, after scale formation. Results showed short-time detection of fluorescence in scales (< 1 year), because of two phenomena: a high number of regenerated scales all along the trout lifespan, and a rapid decrease of fluorescence intensity in scales. However, fluorescence remained detectable for a longer time in fins, where it could be directly observed with a portable device. Substantially high differences in detection rate between streams (between 32% and 96% of marked fish) and between sites (from 0% to 100%) suggest a strong effect of environmental features on fluorescence intensity. Solar radiations are expected to lower fluorescence intensity on exposed fish, reducing thus the rate of detectable marked fish. Nevertheless, in an entirely shaded stream, results showed that more than 95% of stocked trout still displayed detectable fluorescent fin rays, 12 and 24 months after marking.
Consulter en ligne
Suggestions
Du même auteur
