Evaluating the placement of PIT tags in tropical river fishes: a case study involving two Mekong River species

Fish communities are becoming increasingly threatened in many tropical river-floodplain systems due to the construction of dams and other physical barriers. Efficient tagging techniques are urgently needed to better understand the movement ecology of tropical river-floodplain species — both at a fundamental level and in response to the effects of barriers. Passive Integrated Transponder (PIT) tagging has been successfully used to quantify fish movements in many temperate riverine species, but its effectiveness on tropical riverine species remains largely untested. We investigated the potential use of PIT tags in two tropical species from the Mekong River — Pangasianodon hypophthalmus (Striped catfish) and Hypsibarbus malcolmi (Goldfin tinfoil barbs). Two separate, but concurrent, 50-day experiments were conducted on the two species to determine whether (1) the PIT tags can be retained within the fish, without affecting their mortality or growth, and (2) the outcomes for tag retention, fish mortality, and/or fish growth are influenced by the location of the tags in the fish. Results indicated that, for both species, PIT tags can be retained in the chest, gut or shoulder without affecting mortality or growth. This suggests that PIT tags could be successfully used in a range of body locations in Striped catfish and Goldfin tinfoil barbs in the Mekong River. However, the Mekong fishery is a highly important food source for the people of its neighbouring countries — thus, the most suitable tag location in large-bodied species would be the gut region, as the gut, and tag, are most likely to be removed prior to human consumption

The first day of the Cenozoic

Highly expanded Cretaceous-Paleogene (K-Pg) boundary section from the Chicxulub peak ring, recovered by International Ocean Discovery Program (IODP)-International Continental Scientific Drilling Program (ICDP) Expedition 364, provides an unprecedented window into the immediate aftermath of the impact. Site M0077 includes ∼130 m of impact melt rock and suevite deposited the first day of the Cenozoic covered by <1 m of micrite-rich carbonate deposited over subsequent weeks to years. We present an interpreted series of events based on analyses of these drill cores. Within minutes of the impact, centrally uplifted basement rock collapsed outward to forma peak ring capped in melt rock. Within tens of minutes, the peak ring was covered in ∼40 m of brecciated impact melt rock and coarsegrained suevite, including clasts possibly generated by melt-water interactions during ocean resurge. Within an hour, resurge crested the peak ring, depositing a 10-m-thick layer of suevite with increased particle roundness and sorting.Within hours, the full resurge deposit formed through settling and seiches, resulting in an 80-m-thick fining-upward, sorted suevite in the flooded crater. Within a day, the reflected rim-wave tsunami reached the crater, depositing a cross-bedded sand-to-fine gravel layer enriched in polycyclic aromatic hydrocarbons overlain by charcoal fragments. Generation of a deep crater open to the ocean allowed rapid flooding and sediment accumulation rates among the highest known in the geologic record. The high-resolution section provides insight into the impact environmental effects, including charcoal as evidence for impactinduced wildfires and a paucity of sulfur-rich evaporites from the target supporting rapid global cooling and darkness as extinction mechanisms

The first day of the Cenozoic

Highly expanded Cretaceous–Paleogene (K-Pg) boundary section from the Chicxulub peak ring, recovered by International Ocean Discovery Program (IODP) –International Continental Scientific Drilling Program (ICDP) Expedition 364, provides an unprecedented window into the immediate aftermath of the impact. Site M0077 includes ∼130 m of impact melt rock and suevite deposited the first day of the Cenozoic covered by &lt;1 m of micrite-rich carbonate deposite over subsequent weeks to years. We present an interpreted series of events based on analyses of these drill cores. Within minutes of the impact, centrally uplifted basement rock collapsed outward to forma peak ring capped in melt rock. Within tens of minutes, the peak ring was covered in ∼40 m of brecciated impact melt rock and coarsegrained suevite, including clasts possibly generated by melt–water interactions during ocean resurge. Within an hour, resurge crested the peak ring, depositing a 10-m-thick layer of suevite with increased particle roundness and sorting. Within hours, the full resurge deposit formed through settling and seiches, resulting in an 80-m-thick fining-upward, sorted suevite in the flooded crater. Within a day, the reflected rim-wave tsunami reached the crater, depositing a cross-bedded sand-to-fine gravel layer enriched in polycyclic aromatic hydrocarbons overlain by charcoal fragments. Generation of a deep crater open to the ocean allowed rapid flooding and sediment accumulation rates among the highest known in the geologic record. The high-resolution section provides insight into the impact environmental effects, including charcoal as evidence for impactinduced wildfires and a paucity of sulfur-rich evaporites from the target supporting rapid global cooling and darkness as extinction mechanisms.Additional funding from:The European Consortium for Ocean Research Drilling (ECORD) implemented Expedition 364 with funding from the IODP and the ICDP. US participants were supported by the US Science Support Program and National Science Foundation Grants OCE 1737351, OCE 1736826, OCE 1737087, OCE 1737037, OCE 1736951, and OCE 1737199. J.O. was partially supported by Grants ESP2015-65712-C5-1-R and ESP2017-87676-C5-1-R from the Spanish Ministry of Economy and Competitiveness and Fondo Europeo de Desarrollo Regional. B.S. thanks Curtin University for an Australian Postgraduate Award. J.V.M. was funded by Natural Environment Research Council Grant NE/P005217/1. K. Grice thanks Australia Research Council for Grant DP180100982 and Australia New Zealand IODP Consortium for funding. The Vrije Universiteit Brussel group is supported by Research Foundation Flanders (FWO) and BELSPO; P.K. is an FWO PhD fellow.</p