Wildlife Damage Management, Internet Center for


Date of this Version

January 1993


This manual is designed for use in the field to help conservation officers identify fish that have been filleted or skinned. Many North American freshwater gamefish and those caught by commercial fishermen are included. Our goal was to collect six fish of each species for measurement purposes. Several states and provinces including Alaska, Colorado, Florida, Idaho, Iowa, Michigan, Missouri, Nebraska, New York, Ontario, Saskatchewan, Texas, Virginia, Washington, Washington D.C., Wisconsin and Wyoming furnished samples. Fish may vary from location to location; these differences were not corrected for in this manual.

For identification of fish, we will first examine fillets. Fish fillets, in most connotations, are of a fish skinned and cut along one side of the vertebrae. Two fillets (right and left side) are found on an individual fish (two left sides equal two fish, not one). Identification is much easier if the fish is scaled (number of scales may be counted vertically or horizontally) or if ribs are kept with the fillets. Some states and provinces require a one-inch patch of scales to be retained with each fillet. If this skin is removed, you have an illegal, unidentified fish. Some groups of fishes look so much alike that a close examination of scales or a laboratory analysis of flesh is necessary for identification. Shape of fillet, color and rib numbers can vary from species to species. Patterns on scales differ between species and can be used like human fingerprints. Many people fillet fish differently, and pieces can be fit together if necessary. Larger fillets may be cut up into smaller sections, but with smaller fish, the fillet is frequently kept whole. Can fillets be identified? Using an electrophoresis technique, some fish species have been identified by flesh alone. This can take agreat deal of time and many forensic laboratories are not equipped or able to perform this service. Very little research, except for identificationof larval fish, has examined the use of muscle segments or myotomes. A study in France by Blin, Balea and Prudhomme (1953) examined cross-sections of major fish sold at the market place. Cross-sections just behind the head (the end of sternum), at the tip of the anus and midway between anus and tail were taken. This comparison was taken for some of the fish examined and identification can be made to families. Can these fillets be identified without employing any fancy scientific equipment? For many species, the answer is yes. This manual was designed to aid in this task.