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Why External PIT Tags?

Our Hallprint external PIT tags combine the best features of traditional external tags, with significant add-on benefits of encapsulating PIT tags.


The industry has largely embraced PIT tags for a range of applications, and there are a lot of advantages to using them:

  • Virtually unlimited unique IDs

  • Small size allows tagging of small and juvenile fish

  • Automated, rapid and highly accurate tagging data entry

  • Hands-free tag reading

  • Allows passive automated and active hands-free tracking of tagged fish

    • Pass-over streambed antennas

    • Pass-through culvert and dam ladder antennas

    • Modified trawl net antennas

    • Mobile wand readers

    • Raft- or boat-mounted arrays


However, there are some downsides to PIT tags as well:

  • Typically requires fish to be anesthetized for surgical implantation

  • Increased fish handling and longer recovery times

  • Higher incidental mortality rates

  • High tag rejection/shedding rates, particularly in ripe adult fish

  • Unvalidated long-term retention rates

  • Food safety risks to consumptive fishery users

  • Impossible to visually identify tagged fish

    • Angler participation is impossible

    • No way to incorporate video or visual counts of tagged vs. untagged fish

    • Mis-scanned PIT tags are never counted without a secondary mark


There are also some downsides to traditional external fish tags:

  • Printed tag numbers limit the number of unique IDs that can be easily used

  • Manual data entry introduces risk of data entry errors

  • Fish have to be recaptured and handled for any long-term data collection


Using External PIT tags can solve these problems, for a similar initial purchase price, and potentially reduced operational cost of application.

  • Automated data entry with a quick scan significantly improves data quality by reducing manual data entry errors

  • Virtually unlimited unique IDs are available, allowing tracking of individual fish across many years and cohorts

  • Industry standard ISO 134.2 kHz FDX frequency allows tags to be read using most existing infrastructure or readily available equipment. HDX and HF tags also available by request. BYO is also an option.

  • Tag data are easily standardized and shared with collaborators across multiple projects and organizations, such as with the PTAGIS online database system

  • Visible external mark allows quick visual identification of tagged fish

    • Anglers can return tags and contribute valuable data, or release tagged fish unharmed to prevent experimental bias

    • Recapture and monitoring sites can be semi- or fully automated with manual counters or video systems (check out our Count Centralizer© system) to survey both tagged and untagged fish simultaneously

    • If the tag doesn’t scan the first time, operators always know to try again

  • External PIT tags can be passively or actively tracked for all the advantages of a PIT tag, plus possible improvements in read range and detectability

  • Numerous studies have documented high long-term tag retention rates of external tags, far greater than those seen with injected PIT tags

  • Easier and faster tag application times

    • Reduced handling

    • No anesthesia

    • Less staff training requirements

  • Virtually zero incidental mortality on most fish species

  • For spawning salmon, external PIT tags are far less likely to be lost during spawning, and more likely to remain available during post-spawn carcass surveys. They will also be highly visible to researchers conducting redd surveys without any disruption to spawning

  • Tampering and counterfeiting are virtually impossible in applications where data security is a concern (e.g., high value derbies, aquaculture, contentious fisheries, poaching enforcement)

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