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Fish with missing fin

Fishing Wisconsin

The Department of Natural Resources (DNR) fisheries biologists track fish for research purposes. There are various ways DNR marks fish which are part of these research studies:

  • a tag is attached to the fish, or
  • a radio transmitter is implanted, as noted by a wire antenna, or
  • a code wire tag is implanted, as identified by a missing adipose fin.

DNR discourages anglers from tagging their fish.

Should you catch a DNR-tagged fish, it is very important to report the requested information promptly. The information provided by the angler helps DNR to determine fish population estimates, and harvest and exploitation rates. In some cases, these studies have been going on for years. Your cooperation and participation are greatly appreciated.

If you release the fish, please do not remove the tags.

Adipose fin clip

Fish biologists want to learn more about trout and salmon in Lake Michigan to improve rearing techniques and the management of the fishery. When these fish are stocked, they are too small to use conventional tagging techniques to mark them. Over the past two decades, the DNR has utilized coded wire tags (CWTs) to mark numerous study groups of trout and salmon fingerlings. CWTs are very small (i.e., smaller than this minus sign -) pieces of stainless steel wire that are etched with a numeric code and injected into the snout of trout and salmon fingerlings before stocking. To identify the fingerlings which have been implanted with a CWT, the adipose fin is removed as shown below.

Starting in 2010, Wisconsin, along with other agencies, began a mass marking project of Chinook salmon with the main objective of trying to determine the number of naturally reproduced Chinook salmon in Lakes Michigan and Huron. To accomplish this goal the USFWS bought and operates mass marking trailers that automatically remove the adipose fin and inject a coded wire tag into the fish. Chinook salmon were marked this way each year from 2011-2016. Since 2017, stocked Chinooks no longer receive a coded wire tag, but they are still adipose fin clipped. Starting in 2018, stocked rainbow trout have been mass marked with an adipose fin clip and coded wire tag.

The Department is interested in getting heads back from these fish so we can recover the coded wire tag and determine when and where it was stocked. If you catch a rainbow trout or lake trout with only the adipose fin missing and want to provide the head for analysis, please follow the instructions below.

missing adipose fin
This diagram shows a fish with a missing adipose (back) fin.

The requested information and notifying the DNR

If you catch a rainbow trout or lake trout missing ONLY its adipose fin, please follow these instructions.

1) Download and fill out this form [PDF].

2) At a minimum, record the species, source, date caught, capture location, and length. You can also fill out the sex, weight and angler information if you choose to.

3) Put the completed form in a separate bag to protect it and place the form and head into another bag.

4) Freeze the head and then drop it off at one of the following DNR offices or cooperating businesses.

DNR offices

DNR Service Center
2984 Shawano Avenue
Green Bay, WI 54313
Call ahead
(920) 662-5480 - phone

DNR Satellite Center
101 N Ogden Road
Peshtigo, WI 54157
Call ahead
(715) 582-5052 - phone

DNR Satellite Center
110 S Neenah Avenue
Sturgeon Bay, WI 54235-2718
(920) 559-0767 - phone

UW-Milwaukee School of Freshwater Sciences
600 East Greenfield Avenue
Milwaukee, WI 53204
(414) 550-1831
Hours: Vary - call first

Cooperating businesses

You may also freeze the head and drop it off at the following locations:

A&K Feed, Seed & Bait
1616 Shore Drive
Marinette, WI
(715) 732-6100

Peshtigo Shell Gas Station
815 French Street
Peshtigo, WI
(715) 582-3681

Town Marina
8132 Hwy. 57
Baileys Harbor

Howie's Tackle
1309 Green Bay Road
Sturgeon Bay, WI 54235
(920) 746-9916

Accurate Marine and Storage
203 Dodge Street
Kewaunee, WI

Seagull Sports Marina
1400 Lake Street
Two Rivers, WI 54241
(920) 794-7533

The Wharf
733 Riverfront Drive
Sheboygan, WI 53081
(920) 458-4406

Port Washington Marina
106 N. Lake Street
Port Washington
(262) 284-6606

McKinley Marina Fish Cleaning Station
1750 N. Lincoln Memorial Dr.

Kortendick Ace Hardware
3806 Douglas Avenue
Racine, WI
(262) 639-4820

If you include your name and address, DNR may respond with the stocking history of this fish.