MKIV Tag Injector


Coded Wire Tags (CWT)

CWT Fish tags - actual size on human fingerThe CWT is a length of magnetized stainless steel wire 0.25 mm in diameter. The tag is marked with rows of numbers denoting specific batch or individual codes. Tags are cut from rolls of wire by an injector that hypodermically implants them into suitable tissue. The standard length of a tag is 1.1 mm. For very small animals half-length (0.5 mm) are used. For larger specimens or improved magnetic detection, one and a half  (1.6 mm) or double length (2.2 mm) may be utilized.

Salmonid fishes are usually tagged in the snout, but "cheek" muscle and certain other tissue offers superior sites for many other species.

NMT has yet to encounter a fish, of sufficient size, that cannot be tagged. Arctic char Salvelinus alpinus as small as 22 mm total length have been successfully snout-tagged with half-length CWT (Champigneulle, et al. 1987 [Abstract]). Since body muscle also provides a suitable and much larger target than the snout of a char, it appears that smaller fish and other organisms can be successfully tagged. Although designed originally for small fish, Coded Wire Tags have been applied successfully in a number of crustacean studies.

Advantages of CWT system:

  • Can be used in very small animals.
  • Minimal biological impact.
  • High retention rates over the life of the host.
  • Enormous code capacity (batch or individual identification).
  • Tags are inexpensive.
  • Potential for automatic scanning of large samples.

Limitations of the CWT system:

  • Capital equipment is expensive (but can be rented from NMT or borrowed from other agencies).
  • In most applications, tags must be excised, usually from dead animals, for reading decimal codes.
  • Tags usually not externally visible.
  • CWT Tag Formats
  • CWT Injectors
  • CWT Detectors
  • CWT Readers

CWT Tag Formats

tag formats

The decimal coding (etching) allows for either batch or individual identification. Batch codes, identifying a group of animals sharing one or more characteristic, are most commonly used for fisheries management purposes.

Standard CWT have batch coding; the same code is repeated over a specific length of wire. Sequential CWT are designed to identify individuals or small groups; the code advances over a specific length of wire. The use of these sequential tags is somewhat more complex in requiring the saving or "archiving" of a CWT before and after the implanted tag or tags.

NMT produces five formats of CWT.  Download the reading instructions for a complete description of each format.

  • Standard
  • One and a half-length
  • Half-length
  • Sequential
  • Agency-only


Refunds — there are no refunds on orders of Coded Wire Tags.

Standard, Half-length, One-and-a-half-length & Sequential Formats


90-Day Delivery 

2,000 – 9,000
10,000 – 99,000                               
100,000 – 999,000
1,000,000 and over 

**Minimum order 2,000 tags



30-Day Delivery 

2,000 – 9,000
10,000 – 99,000                               
100,000 – 999.000
1,000,000 and over 

**Minimum order 2,000 tags



Agency Only Format


90-Day Delivery 

100,000 and over

**Minimum order 100,000 tags


Agency Only Format


30-Day Delivery 

100,000 and over

**Minimum order 100,000 tags



Precut CWTs  
The tags will arrive ready to use.  Single Shot Tag Injector sold separately

Sold in increments of 100
**Minimum order 200 tags



Precut CWT can be used with a single shot injector for small scale studies and for feasibility studies of the Coded Wire Tag.

Single Shot Tag Injector


Spare needle with push wire



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CWT Injectors

CWT are injected into tissue using the MKIV Tag Injector capable of implanting up to 1000 tags/hour; the semi-automatic Multishot injector achieving rates of several hundred tags per hour; or by using the Single Shot "muzzle loaded" syringe (useful for only small numbers of specimens and requiring pre-cut/magnetized tags).


MKIV Tag Injector

Photograph of the Mark IV coded wire tag injector
MKIV Automatic Tag Injector

Mark IV   fitted with a head mold for snout tagging. Two sizes of head mold, and a head mold base which is available for those wishing to make their own head molds or tagging jigs. The needle projects through the hole visible in the center of the head-mold base.
MKIV fitted with a head mold for snout tagging. The MKIV’s needle projects through a hole in the center of the head-mold base.

The MKIV Tag Injector was developed to handle millions of cycles of tag injections. The tags, which come in continuous wire form on a spool, are automatically cut off, magnetized and injected through a hollow needle. The operator then verifies that the specimen contains a tag by dropping the specimen through a Quality Control Device (QCD) where it flows through a tag detection tunnel. If a QCD  is not available, the magnetic tag can be verified by using any of the detectors NMT makes for that purpose.

  • The MKIV Injector is about 18 pounds (8.2 kg) in weight, 10 inches (25.4 cm) wide, 10 inches (25.4 cm) high and 12 inches (30.5 cm) deep
  • The Power Supply, Tool Kit, Touch Switch, 3 non-custom Headmolds and a hard transit case are supplied with the unit; other accessories are available through NMT
  • The MKIV Injector is constructed of the highest quality materials; it is easily programmed from the keyboard and can mark 600-800 fish per hour
  • The MKIV Injector can inject half length (0.5 mm), standard length (1.1 mm), one and a half length (1.65 mm) or double length (2.2 mm) tags
  • The MKIV Injector can be used with either a Head Mold to position the specimen or a needle support tube for freehand tagging
  • The MKIV Injector operates on 24 VDC. The MKIV's power supply operates from a 100-250 VAC 50/60Hz source. International orders are custom fitted with the appropriate plug.
  • The MKIV Injector carries NMT's standard warranty and can be purchased or rented


CWT Injection Equipment
Discounts on orders of 10 or more each of these items

MKIV Tagging Unit
MKIV Tag Injector with accessories, Quality Control Device with accessories


MKIV Tag Injector
Tag Injector,  Touch or foot switch, Tool kit, Transit case, Instruction manual, 3 non-custom head molds, Power supply, 3K Agency wire for training, 1 pkg of 5 needles


Quality Control Device (QCD)
for the MKIV: Interconnect cable, Transit case, Instruction manual


See Also:




Handheld Multishot Tag Injector

The Multishot Tag Injector is designed to meet the demand for a small, portable, handheld "field" injector to mark small batches of fish or very large specimens. The Multishot is not intended to replace the MKIV Injector which was developed to handle millions of cycles of tag injections.Multishot Tag Injector

The tags are supplied in continuous form on a plastic spool. The Multishot cuts a tag from the spool, magnetizes it and injects it into the specimen. The operator then verifies that the specimen contains a magnetic tag with any of the portable CWT Detectors (e.g. the Wand or V-Detector) made by NMT for that purpose.

  • The Multishot is about 10 ounces in weight, 11 inches long (27.9 mm), 2 inches (5.1 mm) wide and 2 inches (5.1 mm) deep
  • The Multishot has a high grade aluminum housing and many of its components are stainless steel
  • The Multishot can be used to mark 200 to 400 fish per hour
  • multishotThe Multishot can inject standard length (1.1 mm), one and a half length (1.65 mm) or double length (2.2 mm) tags (it can not be used to inject half length tags)
  • The Multishot can be used with head molds to assist tag placement
  • The Multishot carries NMT's standard warranty and can be purchased or rented

The Multishot Field Kit is designed to compliment the Handheld Multishot Injector. This kit contains the most often needed replacement parts required  by users in the field. 



Handheld Multishot injector


See Also:



Multishot Field Kit

The Multishot Field Kit is designed to compliment the Handheld Multishot Injector. This kit contains the most often needed replacement parts required by users in the field. Many of these parts are critical to the performance of the Multishot Hand Injector and can not be purchased elsewhere. This Kit will enhance tagging in remote places, enabling the user to continue a project that may be delayed by minor equipment problems.




Needle Clamping Nut W/Support Tube(1)NEE000015
Idler Roller(1)IDL007838
E-Clips (2)RET014250
#4 Split Washers (2)WAS019680
Pushrod Nuts (2)SPA017090
Pushrod Assembly (1)MUL010433
Pushwires (3)PUS000001
2-56 SHCS w/patch (2)SCR014610
#2 Washers (2)WAS019618
4-40 SHCS (2)SCR014830
4-40 Set Screws (1 ea)SET016615
Pullspring (1)PUL012035
Shoulder Bolts (1 ea)SCR015530
Titanium Cut Lever Alignment Pin (1)PIN011665
Drive Roller Assy (1)DRI005485
Pawl & Spring Assy (1 ea)PAW011290
Alignment Bar (1)PIN011660
Detent, Push Rod Spring (2)SPR017245
Alternate Head Mold Springs(2)SPR017252
Cut Lever / Wire Advance Lever Spring (1)SPR017249
Roller Pressure Arm Spring (1)SPR017256
Wire Advance Lever Stop Set Screw(1)SET016670




Field Kit




Single Shot Tag Injector

single shot

The Single Shot Injector is designed as an inexpensive means of implanting small numbers of Coded Wire Tags (CWTs) for trials of the system and for limited-scale experiments involving only tens or hundreds of animals.

The Single Shot Injector is a simple muzzle-loaded syringe injector. It is intended for laboratory trials and small scale experiments involving up to a few hundred animals.

The Injector is made of sturdy stainless steel and comes with sharpening stone. Spare needles and push wires can be ordered separately.

For larger-scale projects involving thousands of animals the Handheld Multishot Injector or MKIV Injector will be more suitable.








Single Shot Tag Injector






Head Molds

Head molds are designed to position a fish correctly for tag injection. Head molds are specific to a particular size and species of fish.

A wide range of ready-made head molds are available from NMT, as shown in the table below. The size ranges of the molds listed overlap slightly and the size stated is the  middle of the range for which the individual mold is suitable. For example steelhead from a little smaller than 80 per pound (6g) to a little larger than 2 fish per pound (227 g) can be accommodated by the available range.

Head molds for species or sizes other than those listed below can be obtained in two ways. NMT can supply a head mold fabrication kit containing all supplies and instructions to make head molds. Head mold bases are also available for customers supplying their own materials. 

For brown trout (Salmo trutta), head molds for Atlantic salmon (but one size larger) are generally suitable.

Stock Head Mold Sizes


Head Mold Size
(number of fish per pound )

Coho / Chinook 5, 10, 15, 20, 30, 45, 65, 90, 120, 200, 300, 550, 1100
Steelhead 2, 3, 5, 7, 11, 20, 36, 80
Rainbow 5, 8, 12, 18, 27, 50, 90, 200
Pink 2000
Atlantic salmon 7, 9, 11, 15, 25, 30, 50, 100, 120
Lake trout 5, 8, 12, 18, 27, 50, 90
Chum 700


Head Mold Size
(length of fish in mm)

Mullet 45-55, 60-70, 70-80, 100, 120, 140
Sockeye 60, 90
Walleye 55, 65, 125


Not size specific




Fish Size Conversion Chart

The chart below presents size conversions based upon measurements of Chinook Salmon.

Number of fish per pound

Grams per fish

Fish Length



1200 0.33 1.32 3.35
1000 0.45 1.40 3.56
800 0.57 1.52 3.86
700 0.65 1.58 4.01
600 0.76 1.67 4.24
550 0.82 1.71 4.34
500 0.91 1.77 4.50
475 0.96 1.80 4.57
425 1.07 1.87 4.75
400 1.14 1.91 4.85
380 1.19 1.94 4.92
360 1.26 1.97 5.00
340 1.35 2.02 5.13
320 1.48 2.08 5.28
300 1.52 2.10 5.33
290 1.57 2.13 5.41
280 1.62 2.15 5.46
270 1.68 2.17 5.51
260 1.75 2.20 5.58
250 1.82 2.23 5.66
240 1.89 2.26 5.74
230 1.98 2.28 5.81
220 2.07 2.32 5.94
210 2.16 2.36 6.00
200 2.27 2.40 6.10
190 2.39 2.44 6.20
180 2.52 2.49 6.30
170 2.69 2.53 6.40
160 2.84 2.59 6.60
150 3.03 2.64 6.70
140 3.24 2.69 6.83
130 3.49 2.80 7.08
120 3.78 2.85 7.20
110 4.13 2.95 7.45
100 4.54 3.03 7.70
90 5.04 3.13 7.95
80 5.67 3.26 8.30
70 6.48 3.41 8.66
60 7.56 3.56 9.10
50 9.08 3.81 9.70
40 11.54 4.13 10.50
30 15.12 4.51 11.46
20 22.68 5.17 13.13
10 45.36 6.52 16.56
9 50.00 6.73 17.10


Head Mold


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CWT Detectors

Due to their small size, and usual position in opaque tissue, CWT must be located and recovered using specialized magnetic detectors that come in various forms (e.g., Wand, tunnels, V-Detector). Once excised, CWT are visually decoded under magnification of about 10x. CWT are normally dissected from dead/harvested fish, but the method offers considerable opportunity to recover data from living specimens as well:

  • Simply knowing a fish is tagged, as determined by the CWT detector, can provide a simple "yes or no" answer (e.g., identifying hatchery origin fish in a mixed population, etc.).
  • 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 - increasing with animal size - of different "codes"
    (Tipping and Heinricher, 1993).
  • Shallow, and often visible implants of CWT, may be excised without significant damage to the animal
    (Oven and Blankenship 1993).
  • Electronic Detection Products

    Related Product


    The V-Detector operates by detecting small changes in the magnetic field that are caused when a Coded Wire Tagged specimen is moved past the sensors located in the V-shaped sides of the instrument. It is light, rugged and adequately protected to tolerate the usual wet conditions. The detector should be positioned on a firm surface or if you prefer the unit can be mounted using threaded sockets provided.

    The V-Detector:

    • Is about 8 pounds in weight, 14 inches high, 9 inches wide and 7 inches deep
    • Is constructed of high quality marine materials
    • An audible signal and/or light indicates the presence of tags
    • Can detect all sizes of NMT's magnetic tags, including half-length
    • Will operate approximately 100 hours on a single disposable 9-volt alkaline battery
    • Comes with a hard transit and storage case
    • The V-Detector was formerly called the Portable Sampling Detector (PSD) or Field Sampling Detector (FSD)


    V Detector






    T-Wand Detector

    NMT's T-Wand is a rugged Coded Wire Tag (CWT) detector for field use. It is fully waterproof, floats, and is stable in a wide range of temperatures. The T-Wand is a significant advance over the blue Handheld Wand, and we recommend the T-Wand for most field applications that require a portable CWT detector.

    The detection range of the T-Wand is 5.5 cm for a standard length CWT, considerably more than the blue Handheld Wand (3.2 cm). Because of this, the T-Wand is quicker and easier to use than the blue Handheld Wand, fewer tags will be missed, and mouth wanding is not needed or feasible for large salmon. The T-Wand is rubbed against the suspected tag site, and indicates the presence of a CWT with a beep and lights.


    • The T-Wand weighs 1 pound 7 ounces (0.68 kg) and is just over 12 inches (30 cm) long.
    • The volume can be toggled between medium, off and high.
    • Three LED lights are highly visible, even in full sun.
    • Two AA batteries are inserted by unscrewing the handle end cap.
    • The T-Wand is balanced in the hand, making it comfortable for extended use.
    • A fabric belt holster is included.
    • T-Wand Spec Sheet

    The T-Wand is made in Washington, USA. Each T-Wand is packed in a heavy-duty transit case with a fabric holster, wand standard, and instructions.

    You may be eligible for a discount up to $1000 on the purchase price of a new T-Wand if you trade in a blue Handheld Wand. Please contact us for more information.


    T-Wand Detector
    For availability please contact



    Video Instructions

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    Quality Control Device (QCD)

    qcdThe Quality Control Device (QCD) operates as an accessory to the MKIV Coded Wire Tag Injector. After the tag has been implanted by the MKIV injector, the operator drops the fish into the QCD where it flows through a tag detection tunnel. Tagged and untagged fish are automatically sorted through separate outlets. Counters record the quantity of tagged fish. An audible signal alerts the operator when a Mark IV Injector is cycled and the previously tagged fish was not detected by the QCD.

    • the QCD weighs about 40 pounds (18.1 kg), is 30 inches high (76.2 cm), 9 inches wide (24.1 cm) and 45 inches deep (1.1 m) when it is set up and ready to use
    • the QCD is constructed of high quality marine materials
    • the QCD operates through a cable connected directly to the MKIV Tag Injector
    • the QCD connects to standard hose fittings, with a water flow requirement of 3 gallons (11.4 l) per minute
    • the QCD can detect all sizes of NMT's magnetic tags, including half-length
    • lightweight components and folding legs make the QCD easy to transport; many of the plumbing connections use "quick disconnect" fittings
    • a hard transit and storage case is provided
    • the QCD carries NMT's standard warranty and can be purchased or rented


    Quality Control Device






    Tunnel Detectors (R-Series)

    R9500 Detector shown with optional Diverter Gate and Dual Counter

    The Rectangular Tunnel Detectors are the largest of Northwest Marine Technology's complement of detectors. The Rectangular Detectors accommodate large, single fish such as salmonids approaching 50 pounds; the continuous flow of fish such as pollock or herring; or batches of fish such as bushels of shrimp or scallops. The detection capabilities of the rectangular technology are superior to any other detector ever produced.

    There are two models of Rectangular Detectors:

    • The R8000 weighs 64 pounds, is 15 1/2inches wide, 11 7/8 inches high and 41 3/8 inches long. The tunnel's inside dimension is 4 inches x 7 7/8 inches.
    • The R95000 weighs 98 pounds, is 17 1/8 inches wide, 13 inches high and 48 1/2 inches long. The tunnel's inside dimension is 4 5/8 x 9 1/2. 
    • Rectangular Detectors are designed to be rugged while still being lightweight and performing as a precision instrument. A protective transit case is an available option for the R8000.
    • Collapsible aluminum tubular legs can be fitted on either model. 
    • Rectangular Detectors are designed to detect tagged fish moving through the unit within a range of speeds, chosen to accommodate fish sliding down an angled tube under the influence of gravity. A tagged fish is indicated visually via an LED and audibly by a beeper. 
    • Rectangular Detectors can also drive additional instruments such as gates, beepers or lights. 
    • An available option for the Rectangular Detectors is a bolt-on diverter gate for use when sampling single fish such as salmon. Both the detector or the gate can be powered by either batteries or external power. A gate on either model adds approximately 13 inches to the length. 


    R Series Detector R8000


    R Series Detector R9500


    R Series Diverter Gate with Dual Counter


    Quad Counter for R8000 or R9500



    T13 Detector

    T13 DetectorThe T13 is the largest of a new line of tunnel-type Coded Wire Tag (CWT) detectors. It maintains the high sensitivity of the earlier R-Series detectors and their ability to detect a tag in any orientation but accommodates a much larger fish.

    T-Series detectors are designed to plug together with one or more other system components such as a power supply, control box, and a diverter gate using a unified system connector.

    The T13 detector's tunnel is oval with the maximum inside dimensions of 7.5 inches (19cm) by 13 inches (33 cm). It may be used with either the broad or the narrow dimension upright, however the NMT (Northwest Marine Technology) funnel and gate are designed for attaching to the detector when the larger dimension is horizontal.

    For diverting fish, the T13 is supplied with a diverting gate, a control box and a dual counter. The control box controls the settings for the gate, detector and control box functions and records counts of detected tags in up to four different groups; for counting untagged fish the dual counter is required. Using the control box it is possible to adjust the system for a variety of situations, such as fish that move unusually fast or unusually slow.
    When using a gate, the gate and detector are powered with either the NMT 24VDC power supply or with 24V from two standard 12V deep cycle batteries hooked in series.

    Most T13s will be in permanent installations, but the detector may be mounted on a small trailer allowing the detector to be moved around on site.

    If you are interested in a different configuration of the T13 detector please contact Northwest Marine Technology at 360-468-3375 for more information.

    The T13 carries the standard NMT Warranty.


    T13 Detector with control box


    T13 gate with counter




    CWT Detection Standard
    With the Handheld Wand Detector in contact with the CWT Detection Standard, move wand in direction of arrow on instruction label. 


    CWT Detection Standard

    Routine checking of detection equipment during sampling is important to assure accuracy, and gives the operator confidence that the detection equipment is adjusted correctly and is able to detect a tagged fish.

    The CWT Detection Standard was developed for use in determining that NMT electronic detection equipment is functioning properly. Each CWT Detection Standard contains a Coded Wire Tag that maintains an accepted magnetic level.

    The CWT Detection Standard is included with the purchase of any NMT electronic detection device. Additional CWT Detection Standards are available for purchase.

    CWT Detection Standard dowel version is used in testing R Series Tunnel detectors. After setting the detector as discussed in the manual, pass the CWT Detection Standard through the tunnel at 2-3 meters per second to verify setting and function.


    CWT Detection Standard



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    CWT Readers

    Due to the small size of the CWT, tag reading is normally done under a suitable low power ( 20X and 40X ) microscope with magnification.  Handling the tags is greatly assisted by the use of tag reading pencils and reading jigs. Experience has shown that proper lighting is an important component of tag readability.

    NMT offers the following products that assist in reading CWT.

    See Also:

    • APC16 Illuminating and Viewing Coded Wire Tags (PDF)


    MagniviewerThe MagniViewer is a portable, battery operated device used to magnify and view NMT's unique Coded Wire Tags. The MagniViewer combines a twenty five power microscope, a high intensity light, and magnetic reading "pencil" to view both individual tags and spools of Coded Wire Tags.
    The MagniViewer is designed to be small, lightweight and easy to use. The MagniViewer actually fits in the palm of your hand. 

    The following operating instructions demonstrate the ease of use:

    • Turn on the light source by turning the high intensity flashlight handle in a clockwise direction (about 3/4 of a turn).
    • Insert the end of a spool of wire through the tiny funnel guide or place a cut tag on the magnetic end of the pencil and insert into its guide.
    • Adjust the focus to your eye by rotating the microscope and read the code.

    Common uses for the MagniViewer:

    • Determine the format and the code of tags on a spool of wire. For example, if the label from the spool is lost.
    • Demonstrate what a Coded Wire Tag looks like (show your co-workers and constituents).
    • Verify the performance of a tag injector. Examine a cut tag from a MKIV automatic tag injector or a Handheld Multishot Injector to verify that the tag has been cut properly and is readable. For example, the MagniViewer could alert you to a tag that is too short or cut badly at the ends; indicating that drive rollers or cutter may need to be adjusted or replaced.
    • Read a tag's code in the field, or in the laboratory. The portability of the MagniViewer allows it to be easily transported.
    • Read and record the code of a reference tag associated with the use of sequential coded wire tags. ( See application note APC11 PDF )





    CWT Illuminator


    The Illuminator is a newly developed light source specifically designed to aid in the reading of NMT Coded Wire Tags. The Illuminator fits over the NMT brass Reading Jig, and will fit under most microscopes.

    It uses LED technology to provide intense lighting and eliminate shadows that may affect tag readability. The Illuminator comes with its own power supply. The LEDs are expected to have a long lifetime.

    The Illuminator outperforms other models of LED, strobe type or diffuse illumination lights. It is the perfect tool for reading Decimal or Binary Coded Wire Tags.

    To reduce unwanted glare, you may wish to darken the background area of the brass jig with black electrical tape or paint when using with the Illuminator.




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