Natal origin and migration pathways of Mekong catfish (Pangasius krempfi) using strontium isotopes and trace element concentrations in environmental water and otoliths

Abstract

To improve our knowledge of the migration pathway of a highly threatened fish species along the Mekong River, strontium isotope ratios (87Sr/86Sr) and 18 trace element concentrations were measured in the water and in the otoliths of an anadromous catfish, Pangasius krempfi, to infer its natal origin and potential migration pathways. Water was sampled at 18 locations along the mainstream, tributaries and distributaries of the Mekong River. To check for accuracy and precision, measurements of the 87Sr/86Sr ratios and trace element concentrations were then compared in two laboratories that use different analytical methods. Differences in trace element concentrations between locations were not significant and could not, therefore, be used to discriminate between migration pathways. However, the Mekong mainstream, tributaries and distributaries could all be discriminated using Sr isotopes. The 87Sr/86Sr profiles recorded in P. krempfi otoliths showed that there were three contingents with obligate freshwater hatching and variable spawning sites along the Mekong mainstream, from Phnom Penh (Cambodia) to Nong Khai (Thailand) or further. After hatching, the fish migrated more or less rapidly to the Mekong Delta and then settled for most of their lifetime in brackish water. Spawning habitats and migration routes may be threatened by habitat shifts and the increasing number of hydropower dams along the river, especially the contingents born above Khone Falls (Laos). The conservation of P. krempfi, as well as other migratory fish in the Mekong River, requires agreements, common actions and management by all countries along the Mekong River. This study highlighted the importance of using both Sr/Ca and 87Sr/86Sr ratios to understand life history of anadromous fishes as the 87Sr/86Sr ratio in the water was shown to be less effective than the Sr/Ca ratio in identifying movements between different saline areas.

Reading the biomineralized book of life: expanding otolith biogeochemical research and applications for fisheries and ecosystem-based management

“…Sr:Ca or Ba:Ca) (e.g., Elsdon et al 2008;Gillanders et al 2015;Walther & Limburg 2012). Migrations that occur solely within freshwater require a different approach, and changes in otolith 87 Sr/ 86 Sr ratios can represent movements of individuals between isotopically distinct regions (Barnett- Johnson et al 2008;Hegg et al 2013), including within and among rivers (Brennan et al 2019a;Hermann et al 2021;Humston et al 2017;Tran et al 2021;Walther & Limburg 2012). This latter approach has recently revealed exceptionally long-distance migrations (> 8000 km) by goliath catfish (Brachyplatystoma rousseauxii) in the Amazon Basin, including natal homing (Duponchelle et al 2016).…”

Provenance, transport, and the fate of organic matter and sediments drained through Himalayan Rivers in Nepal

“…The chemical recoveries are better than 90% for both Sr and Nd based on long-term measurements on international reference materials (soil: NIST SRM 2709a and 2710a; river sediments: JSD-1 and JSD-2; rock: BCR-2). The Sr and Nd isotope compositions were measured by an MC-ICP-MS (Neptune PLUS, Thermo-Fisher Scientific) at the Institute of Earth Sciences, Academia Sinica, Taiwan (Huang et al, 2014;Howe et al, 2018;Wu and Huang, 2021;Tran et al, 2021). Mass fractionation was corrected with the exponential law for 86 Sr/ 88 Sr (0.1194) and 146 Nd/ 144 Nd (0.7219), respectively.…”

Fish Diversity along the Mekong River and Delta Inferred by Environmental-DNA in a Period of Dam Building and Downstream Salinization

“…However, these species are known to undertake seasonal migration for feeding or reproduction [61], which could mean that a time-limited eDNA sampling campaign may artificially restrict the spatial range of distribution of a species. Using the ratio otolith 87 Sr/ 86 Sr and Sr/Ca in Pangasius krempfi, Tran et al [62] demonstrated that this species is an anadromous fish that breeds in the freshwater regions in the Mekong mainstream along the Laos-Thailand border or in Cambodia, and then at early stages, migrates to the Mekong Delta, and spends most of its lifetime in the brackish and marine environments. Concerning Labeo chrysophekadion, Sokheng et al [61] assumed the presence of several populations with different behavior in the Mekong River.…”