A promising new method of marking larval freshwater fishes with enriched stable isotopes by means of injecting the maternal parent with the marking agent was investigated. The 138 Ba: 137 Ba ratios in the otoliths of larval golden perch Macquaria ambigua were compared to determine the effect of injecting female broodstock with different dosages of enriched 137 Ba at various times before spawning. There was 100% mark success in the progeny of fish injected with 20 μg g −1 of enriched 137 Ba 24 h before inducing spawning with hormones and 40 μg g −1 administered at the same time as inducement of spawning. Injection of 40 μg g −1 enriched 137 Ba 21 days before spawning resulted in only 81% mark success and suggests rapid elimination of barium in M. ambigua. Injection with enriched 137 Ba did not significantly affect the fertilization rate, number of fertilized eggs or hatching rate compared with long-term hatchery records. These results suggest that transgenerational marking is an effective and affordable means of mass-marking larval fishes. Thousands of larval fishes can be permanently marked with a unique artificial isotopic mark via a single injection into the maternal parent, thus avoiding the handling of individual fishes or having to deal with chemical baths. Because no single mark or tagging method is suitable for all situations, transgenerational marking with enriched stable isotopes provides another method for researchers and managers to discriminate both hatchery-reared and wild fishes.

We conducted a series of osmotic induction procedures for marking golden perch Macquaria ambigua with calcein and alizarin red S (ARS), evaluated the factors that influenced mark quality, and tested for any effects on fish growth and mortality. Three aspects of the marking protocols were considered: immersion time in a 5% salt solution (0, 5, or 10 min), immersion time in the fluorescent dye (5 or 10 min), and concentration of the dye (low or high). Quantitative estimates of mark intensity using photographs of marked fish were made with image analysis software. Although there were some significant interactions between factors, salt immersion was generally the primary determinant of mark intensity, followed by dye concentration and dye immersion time. Fish marked with calcein did not have higher mortality rates than unmarked fish and had significantly higher growth rates. The highest‐exposure ARS treatments resulted in higher mortality and lower growth rates than for unmarked fish. Following this result, a lower‐exposure ARS marking protocol was tested, which resulted in no detectable effects on mortality or growth rates while still producing high‐quality marks. Although further study of the long‐term retention of marks under field conditions is required to understand the limitations of the chemical marking methods examined in this study, our results suggest that the methods would greatly enhance our knowledge of the outcomes of fish stocking.

Stocking of native fishes is conducted to augment riverine fisheries in many parts of the world, yet most stocking activities are conducted without empirical information on their effectiveness or impacts. In the Murray–Darling Basin (MDB), Australia, stocking has been underway for several decades to maintain recreational fisheries. We stocked chemically tagged golden perch (Macquaria ambigua) fingerlings in three rivers to determine the proportions of stocked fish within populations of the species. Stocked sites were monitored for up to 5 years in the Murrumbidgee River, Edward River and Billabong Creek and non-stocked sites were monitored in the Murray River. Catch per unit effort of stocked year classes increased substantially in Billabong Creek, with stocked fish contributing 100 (2005), 79 (2006) and 92% (2007). Chemically tagged fish comprised 18–38% of the respective age classes in the Murrumbidgee and Edward rivers and there was little evidence of natural recruitment in the non-stocked Murray River. Tagged fish generally attained the legal minimum size within 4 years and had dispersed up to 60km from the original release location. Our results demonstrate that artificial stocking has the potential to strongly influence the abundance and population structure of golden perch in rivers of the MDB.