Choosing the right tagging system for your program

The following table is a guide to the general properties of NMT’s tags. However, each tagging project has unique objectives and characteristics that may not be reflected here and will affect the choice of the most appropriate tag. More detailed explanations are available by clicking on the hyperlinks for each category. After reading the table, please also review relevant publications and contact NMT’s Biological Services to discuss your needs.

 

Coded Wire Tags (CWT)

Visible Implant Elastomer (VIE)

Visible Implant Alpha (VI Alpha)

Project Size

200 to millions

100 to ~1 million

100 to thousands

Suitable for Small Species or Early Life Stages

Usually

Usually

Sometimes – this is species dependent.

Tag Retention

Typically very high for the life of the animal.

Variable by species and size at tagging – review relevant publications.

Internally Injected

Yes

Yes

Yes

Anesthetic Required

Yes, for manual tagging projects, but not if AutoFish is used.

Usually. Some centrarchids can be held for tagging.

Yes

Injection Methods

  • Single Shot
  • Multishot
  • Mark IV
  • AutoFish
  • Manual
  • Air Driven Elastomer Injection System
  • Manual

Number of Colors

Not applicable

Six fluorescent; four non-fluorescent

Four fluorescent

Externally Visible

Limited scope. CWT are not usually visible when injected. In a few cases, they can be put into clear tissue and will remain visible.

Yes

Yes

Batch Identification

Yes

Yes

No

Individual Identification

Yes, by using sequential tags.

Yes, by combining tag locations and colors.

Yes

Number of Unique Individual Codes

Unlimited

Depends on the number of colors, tags, and tag locations used.

10,000 (2,500 alphanumeric codes in each of four colors)

Tag Recovery

Use external mark or electronic detection to sort tagged and untagged animals.

Visible with naked eye, visibility of fluorescent colors is enhanced with the VI Light.

Visible with naked eye, visibility is enhanced with the VI Light.

Can Untrained Samplers (e.g. Sports Fishers) Identify Tagged Animals?

We recommend that projects involving our tags use scientific sampling with trained samplers to recover the tags. Unless an external mark, (e.g. fin clip) is used to identify a tagged animal, untrained samplers are usually unlikely to find a tag.

Code Recovery

Remove tag and read under microscope.

Tags are externally visible.

Tags are externally visible.

Recover Data From Live Animals

Limited

Yes

Yes

Scope of Species Tagged

 

Extensive Use

Fish
Crustaceans

Fish
Crustaceans
Amphibians

Fish
Crustaceans
Amphibians

Occasional/Emerging use

Amphibians
Birds
Echinoderms
Insects
Molluscs
Annelids
Reptiles

Annelids
Birds
Cephalopods
Reptiles

Reptiles

 

 

  • Project Size
  • Suitable for small species or early life stages
  • Tag Retention
  • Internally Injected
  • Anesthetic Required
  • Injection Methods
  • Number of Colors
  • Externally Visible
  • Batch Identification
  • Individual Identification
  • Number of Unique Individual Codes
  • Tag Recovery
  • Can Untrained Samplers Iidentify Tagged Animals?
  • Code Recovery
  • Recover Data From Live Animals
  • Scope of Species Tagged

Project Size

The number of animals to be tagged and the time available for tagging them affect the suitability of a given type of tag.

The development of different injection methods, from manual injection of individual tags to robotic tagging systems, has made CWT adaptable to a wide range of project sizes. Small-scale and feasibility studies can be accomplished using precut tags that are individually injected. The use of sequential CWT facilitates projects where a number of small groups must be identified (see Application Note APC 05). Larger projects are accomplished by using semi-automated or automated tagging systems.  The upper limit to the size of a CWT project is typically determined by the amount of time available for tagging with the equipment on hand.

The Manual Kits for VIE are well adapted to small and medium sized projects using manual injection and for easy portability for field projects. Larger projects, up to about a million animals, have beenaccomplished by using the Air Driven Elastomer Injection System.

VI Alpha Tags are typically used in projects of hundreds to a few thousand animals, or larger projects when the tagging spans across seasons. They are not well suited to very large projects because of the slower rate of tag injection.

 

Suitable for small species or early life stages

CWT and VIE are widely used for tagging early life stages and small species. CWT are highly versatile in the range of animal sizes that they can be used with. CWT are available in various sizes and can be applied to fish as small as newly hatched salmonids. While there is no upper size limit to fish that could be tagged with CWTs, large fish are usually tagged with electronic tags. When tagging early life stages of species that will grow very large, such as sturgeon, care must be taken to put the tags in a location where they will still be within the range of electronic detection at recovery.

VIE tags are also highly versatile in this regard. Frederick (1997) [Abstract] successfully tagged reef fish as small as 8 mm. We've developed a short article about the key points to consider when tagging very small fish with VIE.  (see Application Note APE 03).

VI Alpha tags have definite minimum size limitations, and while this varies among species, generally, the animals must be considerably larger than those that can be tagged with CWT or VIE. For example, in salmonids, tag retention is best when the fish are about 150 mm or larger, but sticklebacks of 40 mm are successfully tagged with VI Alpha.

 

Tag Retention

Tag retention with all tag types varies depending on the species tagged, the size of the animal at tagging, and the experience of the tagger. We recommend that you review published literature describing techniques for tagging your species and that wherever possible, you estimate tag retention rates. If publications are lacking, we highly recommend that tag retention studies precede applied uses of the tags. NMT Biologists are available to help evaluate the suitability of your species for any of our tags.

 

Internally Injected

All of NMT's tags are internally injected. This method of tag application avoids tag loss and study bias associated with percutaneous wounds and for VIE and VI Alpha, have the advantage of remaining externally visible. Numerous studies for all tag types show that they have little effect on the survival and behavior of the host.

Anesthetic Required

While there are a few cases when fish can be held and tagged without anesthetic, it is nearly always required.  We find that unanesthetized fish react to the prick of the needle which reduces tag retention due to torn tissue, has the potential to injure both the fish and the tagger, and generally slows the tagging operation. The use of anesthetic also reduces stress that may be caused by handling. However, it also requires that the fish be provided with a suitable place to recover from the anesthetic before release and planning for compliance with regulations on their use.

Injection Methods

Coded Wire Tags can be injected with a variety of methods each suited to different circumstances. The Single Shot Tag Injector is used with Precut Tags for small projects and feasibility studies. The Handheld Multishot Injector is used for medium to large scale projects where electricity is unavailable or where a less complicated injector is a necessity. The Mark IV Tag Injector is used in large scale projects for the fastest tagging, and is the injector also used in the robotic AutoFish System.

Sustained tagging rates of 800 animals per injector per hour are typical for Mark IV production tagging of small salmon and striped bass. Tagging with a Handheld Multishot Injector is usually about half as fast.

Tagging rates with Sequential CWT are similar to Standard CWT but the tag "archiving" process (requiring saving the tags between groups or individuals) slows down the tagging process. Tagging speed is slowest with individual identification and increases with increasing group size.

VIE Tags can be injected manually using a syringe or with the Air Driven Elastomer Injection System (ADEIS) which uses compressed air to force the elastomer material from the syringe. The VIE Manual Kits are typically used in smaller projects, where one tagger is injecting hundreds, rather than thousands of fish per day, or where tagging is done in the field. Projects where thousands of fish are tagged in a day often use the ADEIS because of the increased speed and ease of tagging.

Sustained tagging rates of 600 tags/marks per hour can be achieved with the Air Driven Elastomer Injection System. Injection with the Manual Elastomer Injector is usually about half as fast.

VI Alpha Tags must be individually loaded into a syringe-like injector and implanted into the animal. Sustained tagging rates of 100 tags per hour can be achieved.

 

Number of Colors

VIE is available in six fluorescent and four non-fluorescent colors. The fluorescent colors are highly visible under ambient light and provide the option of greatly enhanced tag detection when fluoresced with the VI Light. Choosing the right colors is important to the success of your experiment. Further information is available at VIE Color Selection and NMT's Biologists are pleased to help you in this regard.

The new VI Alpha Tags are available with black letters on a fluorescent red, orange, yellow, or green background. The visibility and readability is enhanced with NMT's VI Light.

 

Externally Visible

Typically, CWT are not externally visible. There is limited opportunity for placing the tags into transparent tissue such that they remain visible (Oven and Blankenship 1993 [Abstract]), but even in this case, the tag must be excised for the code to be read.

VIE Tags provide external visibility, and can often be observed by divers (Frederick [Abstract]), and from the surface in free swimming fish (Bonneau, et al. 1995 [Abstract]). See VIE Tag Detection  [for more details about maximizing tag detection.

VI Alpha tags are externally visible. Tag visibility and readability are both improved by fluorescing them with the VI Light.

Batch identification

Standard CWT designate "batches" of specimens, (large numbers of specimens with the same code), so they are generally not used for individual identification. Anatomical location, as determined by Wand detection, can provide a limited numbers of unique codes (Tipping and Heinricher 1993 [Abstract]). CWT offer very high potential for stock assessment (Blankenship and Leber 1995 [Abstract]). This has been demonstrated for Pacific salmon (Johnson 1990 [Abstract]), Pacific Herring (Schweigert and Flostrand 2000 [Abstract]), New Zealand snapper Pagrus auratus, and red drum (Willis et al. 1995 [Abstract]). Developments in CWT magnetic detection equipment have increased the potential for automated recovery, even when processing literally tons of specimens (Schweigert and Flostrand 2000 [Abstract]).

VIE - The high application and retention rates of VIE tags provide potential uses for stock assessment.

VI Alpha tags provide individual identification so are not recommended for stock assessment.

 

Individual identification

Sequential CWT are used to identify individuals or small batches. Precut sequential Coded Wire Tags offer an inexpensive option for feasibility and small-scale studies. (see Application Note APC05 PDF 49K)

VIE tags are primarily used for "batch" identification but can provide individual identifications by varying locations and colors. For example, two marks per specimen, four colors and six locations could result in 420 unique codes.

VI Alpha - The alphanumeric code of these tags provides individual identification.

Number of Unique Individual Codes

By using sequential Coded Wire Tags, animals can be individually identified, or small batches can be identified. There is essentially an unlimited number of sequential codes that are available.

The number of individual codes that can be generated using VIE is dependent on the number of tag locations, the number of tags per animal, and the number of colors used. NMT has created an application – the VIE Color Code Generator that you can use to calculate the number of codes.

VI Alpha Tags are available in four colors, each with 2500 alphanumeric codes.

 

Tag Recovery

A critical factor in the design of tagging experiments and choice of methods is the manner of recovery. Fisheries managers often state that returns from fishermen are critical to the success of the project, and that tags must therefore be large and colorful. However, such tags introduce an unknown and potentially serious bias on the survival, growth and behavior of the animal. Also, fishermen may not notice even large tags, they may forget or not get around to responding, or they may choose not to report from concern of being further regulated. In one study, fish in anglers' catches were secretly tagged after capture. In spite of rewards being offered for return of tags, only 29% of the tags were reported (Green et al., 1983 [Abstract]). Similar studies, using "seeded" catches have consistently shown significant, but unpredictable, levels of non-reporting of external tags in commercial and recreational fisheries (Konstantinov 1978, Kleiber et al. 1987[Abstract] and Frusher and Hoenig 2003 [Abstract]). Even if all recaptures are reported, it is difficult to establish the true size of the "sample" of which the tagged recaptures formed a part.

A more robust statistical approach is for the researcher to scan samples of fish catches for marked individuals. Such sampling can be planned and appropriately stratified to address specific questions and to obtain reliable and unbiased answers. Although this approach involves an additional phase in the project it can be highly cost-effective since a reasonable volume of robust data may be much more valuable than a larger volume of doubtful validity. The NMT fish marking systems are all particularly suited to this latter approach, tagged , "flagged" by adipose fin clipping, can be noticed and reported by fishermen. A useful discussion of these and other aspects of fish tagging programs is provided by Bergman, et al. (1992) [Abstract].

Systematic Sampling Recovery

CWT - Pacific and Atlantic salmon sampling programs, (as well as those for other salmonids), have primarily involved the use of clipped adipose fins for collection of tagged heads/snouts (Johnson 1990 [Abstract]). With the implementation of mass marking (removal of the adipose fin to indicate hatchery stocks) and selective fisheries (selectively harvesting abundant hatchery stocks) in the Pacific Northwest, Coded Wire Tag recovery now relies on electronic detection. 

Tag recovery programs for striped bass, white seabass, lobster, paddlefish and others rely on hand operated magnetic detectors and tubes. The feasibility of automated recoveries from a herring fishery is described by Morrison (1990) [Abstract], Schweigert and Flostrand (2000) [Abstract].  Fishery samplers now use either the Handheld  Wand or R-Series Coded Wire Tag detectors for automated tag detection in many species.

VIE tags can be used with fluorescence enhancing light to identify stocks of adult Chinook salmon tagged as fingerlings. (see Selected VIE References by Family: Salmonidae )

VI Alpha - The visibility of these fluorescent tags in ambient light and the ability to be enhanced with blue LED light is an advantage.

 

Can untrained samplers (e.g. sports fishers) identify tagged animals?

In general, NMT's tags are not well suited to voluntary tag recovery programs by untrained samplers. The tags are typically too inconspicuous or require specialized equipment for reliable detection. Further, researchers have been concerned that relying on voluntary recoveries will bias the recovery data (see discussion in the Tag Recovery section, above). For robust studies, we recommend that tag recovery be accomplished by scientific sampling with trained observers.

In some instances, it may be possible to increase the probability that untrained samplers can recover the tags by using a second external mark. While this does not eliminate the bias caused by using voluntary recoveries, it can increase the sample size. For example, in the Pacific Northwest of the United States, the excision of the adipose fin provided a "flag" for tag returns for more than 20 years (Johnson 1990 [Abstract]). Anglers were encouraged to return the snouts of fish missing their adipose fins – the CWT had been implanted into the snouts. In another example, CWT were implanted into the distal portions of paddlefish rostra (Heinricher and Fiss 1996 [Abstract]), and incentives were used to encourage anglers to return the rostra of any landed fish. This program provided more representative data relating to the occurrence of tagged fish.

Visible Implant Tags – Recoveries of VIE and VI Alpha tags by voluntary returns are rarely reported. Blankenship and Tipping (1993) [Abstract] reported on the voluntary returns of coastal cutthroat trout tagged with VI Alpha Tags by anglers.

 

Code Recovery

Standard and Sequential CWT must be excised for the code to be read. In a few instances, shallow implants of CWT into transparent tissue remain visible (Oven and Blankenship 1993 [Abstract]), but the tags cannot be read in situ.

VIE tags are externally visibility, can be observed by divers (Frederick [Abstract]), and from the surface in free swimming fish (Bonneau, et al. 1995 [Abstract]). The visibility of the tags is maximized when they are fluoresced with the VI Light in the dark.

VI Alpha tags are externally visible. The visibility and readability of the tags are maximized when they are fluoresced with the VI Light in the dark.

 

Recover Data From Live Animals

CWT are normally dissected from dead fish, however they can be benignly removed from shallow implants (Oven and Blankenship 1993 [Abstract]). Also, specific location (e.g., left cheek, right cheek, nape, origin of dorsal fin, etc.) of the implanted CWT, as determined by a Wand Detector, can provide a number of different "codes" (Tipping and Heinricher, 1993 [Abstract]).

VIE tags can be read in either live or otherwise intact specimens. Fluorescence facilitates recovery when the tag has become obscured by tissue pigmentation (Josephson et al. 2008 [Abstract]).

VI Alpha tags can be read in either live or otherwise intact specimens. Fluorescence facilitates reading when tag has become obscured by tissue pigmentation.

 

Scope of Species Tagged

CWT, VIE, and VI Alpha are used in hundreds of different species, and they are continually being tried with new species. We encourage researchers to review the published literature and to evaluate retention in new species before applied use begins. NMT's biologists are available to advise on the use of any of our tags in your species and can often provide unpublished reports about the use of our tags.