Fish marking methods are an essential tool in fisheries management and research. They allow tracking of stock levels and migration movements, and help in the definition of protected areas. The use of stable isotopes of elements such as C, O, N, S, and Sr have been used to trace the origin and movement of different species by measuring the isotopic ratio in scales or muscle tissue, but this technique does not allow differential marking of individual fish.

J. Ignacio Garcia Alonso and co-workers, University of Oviedo, Spain, have developed a marking procedure that can be made individual-specific and allows identification of offspring from a single individual or a group of individuals. They used two enriched barium isotopes, ¹³⁵Ba and ¹³⁷Ba, at a given and selectable molar ratio. The procedure was tested on brown trout seven months or seven day before spawning to compare the long- and short-term efficiency. An injection of 0.3 mg of Ba/kg of body mass into female trout — even when they were not gravid — resulted in 100 % successful marking of their first batch of offspring after injection.

This represents a new and important advance in transgenerational isotope marking.

• Individual-Specific Transgenerational Marking of Fish Populations Based on a Barium Dual-Isotope Procedure,
  G. Huelga-Suarez, M. Moldovan, A. Garcia-Valiente, E. Garcia-Vazquez, J. I. Garcia Alonso,
  Anal. Chem. 2011.
  DOI: 10.1021/ac201946k