Article pubs.acs.org/est
Geographical Origin of Amazonian Freshwater Fishes Fingerprinted by 87Sr/86Sr Ratios on Fish Otoliths and Scales Marc Pouilly,*,† David Point,‡ Francis Sondag,‡ Manuel Henry,‡ and Roberto V. Santos§ †
IRD (Institut de Recherche pour le Développement), UMR BOREA (MNHN, IRD, CNRS, UPMC), F75005 Paris, France IRD (Institut de Recherche pour le Développement), UMR GET (Université de Toulouse III, CNRS, IRD), F31400 Toulouse, France § Laboratório Geochronos, UnB/IG, Brasília, DF, 70910-900, Brazil ‡
ABSTRACT: Calcified structures such as otoliths and scales grow continuously throughout the lifetime of fishes. The geochemical variations present in these biogenic structures are particularly relevant for studying fish migration and origin. In order to investigate the potential of the 87Sr/86Sr ratio as a precise biogeochemical tag in Amazonian fishes, we compared this ratio between the water and fish otoliths and scales of two commercial fish species, Hoplias malabaricus and Schizodon fasciatus, from three major drainage basins of the Amazon: the Madeira, Solimões, and Tapajós rivers, displaying contrasted 87 Sr/86Sr ratios. A comparison of the 87Sr/86Sr ratios between the otoliths and scales of the same individuals revealed similar values and were very close to the Sr isotopic composition of the local river where they were captured. This indicates, first, the absence of Sr isotopic fractionation during biological uptake and incorporation into calcified structures and, second, that scales may represent an interesting nonlethal alternative for 87Sr/86Sr ratio measurements in comparison to otoliths. Considering the wide range of 87Sr/86Sr variations that exist across Amazonian rivers, we used variations of 87Sr/86Sr to discriminate fish origin at the basin level, as well as at the sub-basin level between the river and savannah lakes of the Beni River (Madeira basin).
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and migration patterns,5 as they may replace calcium in fish aragonite and hydroxyapatite. To date, the use of biogeochemical tracers in calcified structures has mainly focused on diadromous and marine fish species.6−8 Whereas the number of studies involving freshwater species or continental phase of diadromous species is increasing for temperate systems,9−11 this approach is rarely employed for tropical regions.11 We propose to test their potential of application for tropical freshwater fishes of the Amazon system, where they could be used to retrieve useful information on fish ecology and migration at the level of large regional basins. Strontium isotope ratio (87Sr/86Sr) is a powerful tracer that can be used to gain better understanding of the biogeochemical processes linked with the calcium cycle.12 Sr is an alkaline earth element that has four isotopes, among which the isotope 87Sr is radiogenic and formed by the radioactive decay of 87Rb (rubidium) at a decay rate of 4.88 × 109 years.13 Since Rb tends to be concentrated in the Earth’s crust and Sr tends to be concentrated in the mantle, old reworked crustal rocks usually display higher and distinct 87Sr/86Sr ratios. On the contrary,
INTRODUCTION
Understanding fish natal origin and life history is a key challenge for fisheries, conservation, and ecological sciences. This knowledge may contribute to more precise definition of the migration routes and critical habitats of fish species, and it is also particularly relevant for establishing stock management strategies. Patterns of fish migration and habitat use vary greatly between species and even between individuals. In the Amazon, fish migration patterns are very difficult to observe, characterize, and model because of the size, fragmentation, and the complexity of the multiple basins that exist in this vast region. Longitudinal migrations of large catfish may exceed 5000 km,1 but for many species, seasonal lateral migrations between floodplain and river habitats have also been hypothesized.2,3 Fish calcified structures such as otoliths, vertebrae, and scales grow continuously throughout the lifetime of fishes, representing daily, seasonal, or annual sequential accumulations of layers or growth rings. These structures can be used to determine the age, growth patterns, life history, and migratory history for several fish species.4 Otoliths are composed of aragonite (calcium carbonate) whereas scales and bones are composed of hydroxyapatite (calcium phosphate). When present in the environment under bioavailable forms, elements like barium, strontium, lead, and zinc can serve as tracers of fish natal origin © 2014 American Chemical Society
Received: Revised: Accepted: Published: 8980
January 6, 2014 June 27, 2014 June 27, 2014 June 27, 2014 dx.doi.org/10.1021/es500071w | Environ. Sci. Technol. 2014, 48, 8980−8987
Environmental Science & Technology
Article
Figure 1. Mean 87Sr/86Sr ratio in water (
