Discrimination of wild and hatchery trout by natural chronological patterns of elements and isotopes in otoliths using LA‐ICP‐MS

Abstract

The potential to discriminate between wild and hatchery trout [Salmo trutta f. fario L. and Oncorhynchus mykiss (Walbaum)] by chronological microchemical patterns of different otolith regions was tested. Central and rim regions of otoliths were analysed for life stage specific elemental patterns of strontium (Sr), sodium (Na) and calcium (Ca) as well as of 87 Sr/ 86 Sr ratios using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Classification to life stage specific habitats was achieved with 100% accuracy by 88 Sr/ 43 Ca, 23 Na/ 43 Ca and 87 Sr/ 86 Sr ratios resulting in a discrimination of hatchery fish from wild fish. 87 Sr/ 86 Sr ratios and Sr concentration in otoliths were positively correlated with the ratio and amount in the water. Na content in otoliths did not directly reflect the concentration in the water, although the 23 Na/ 43 Ca ratio in otoliths contributed to the discrimination. Clear differences in otolith chemistry were found for fish experiencing different geological units or a groundwater-fed environment in a hatchery. Natural chronological microchemical patterns in otoliths proved to be a valuable tool for discriminating wild and hatchery fish without the necessity to use marking methods. LA-ICP-MS is well suited for this application because of its limited need for sample preparation, its potentially high sample throughput and the possibility of simultaneous measurement of multiple elemental and isotopic fingerprints. K E Y W O R D S : hatchery fish, laser ablation, management, natural chemical mark, otolith microchemistry.

Otolith elemental and Sr isotopic composition as a natal tag for Biwa salmon Oncorhynchus masou subsp. in Lake Biwa, Japan

“…1). Such a marked variation in otolith chemistry between individuals separated on a small scale has also been reported in Chinook salmon Oncorhynchus tshawytscha from California's Central Valley, USA (Barnett-Johnson & Pearson 2008), brown trout Salmo trutta fario and rainbow trout O. mykiss in southern Austria (Zitek et al 2010), rainbow smelt Osmerus Sr ratio is determined by the ratio in the ambient water, which itself reflects geological characteristics such as the age and composition of 87 Rb, the otolith ratio in the fish should vary if the geological char acteristics of their habitat waters are different (Ken nedy et al 1997, 2000, Ingram & Weber 1999, Ama kawa et al 2012. Nakano et al (2008) We found that elemental composition could also discriminate the sampling locations for individual fish with a high level of accuracy similar to that based on the data combined with 87 Sr/ 86 Sr ratios.…”

Assessment of international reference materials for isotope-ratio analysis (IUPAC Technical Report)

“…Owing to this isotopic invariability, changes in the R( Sr, for Rb/Sr dating or studies of material origin. Stable isotopic variations of strontium are used in provenancing water [244] and food [245,246], for studying biological migration [247] and environmental cycles [248,249], and in archaeometry [250] and forensic science [244]. Marine calcium carbonates have been used to investigate equilibrium or kinetic isotope effects [236].…”

Inductively Coupled Plasma Mass Spectrometry

“…For example, Woodhead et al presented a method to study the isotopic composition with spatial resolution in fish otoliths -incrementally growing earstones of fish, which record environmental information over its life history -using LA-MC ICP-MS. 537 Zitek et al applied a similar method to monitor migration patterns and provenance of freshwater fish. 538 In the context of fish ecology and management, stable isotope tracers have also been used to batch-mark the progenies of one specific mother fish. This transgenerational marking results in an alteration of the isotopic composition of the selected element in the core of the otoliths of all offspring, which can be revealed by using laser-ablation sampling.…”