Fin spine chemistry as a non-lethal alternative to otoliths for stock discrimination in an endangered catfish

Abstract

Trace element:Ca (Ba:Ca, Mg:Ca, Mn:Ca and Sr:Ca) ratios in water and last growth intervals (outer 45 µm) of dorsal spine and otolith edges from Genidens barbus collected in 3 study areas (Brazil, Argentina−Uruguay and Patagonia) were compared to determine whether the spine can provide a non-lethal natural marker alternative to otoliths for this endangered species. We found an association between calcified structures and the availability of some element:Ca ratios in water. Among the measured element:Ca ratios, a strong correlation in Ba:Ca between outer edges of fin spines and otoliths was found (r 2 = 0.87, p = 0.0001), whereas Mg:Ca, Mn:Ca and Sr:Ca ratios were weakly correlated between structures (0.09 < r 2 < 0.20, 0.0006 < p < 0.02). Several ratios were significantly different among sites for otolith and spine edge (p < 0.05). Permutational multivariate ANOVA (p < 0.05) and quadratic discriminant analysis (QDA) proved highly effective for characterizing differences in otolith and spine edge compositions between sampling sites (mean classification rates: 84.2 and 90.1% for otolith and spine edge, respectively), suggesting that both structures can be used as habitat markers. To identify the possible contribution of multiple stocks to the different areas, we performed QDA for the complete last year of a fish’s life. Classification rates were high for both structures, averaging 79.6 and 81.2% for otolith and spine, respectively, suggesting the existence of new stocks in Patagonian waters. Spine chemistry seems to be an acceptable non-lethal advantage over otoliths to study different biological aspects of catfish.