How Identification Keys Work
Last Update/Review: August 6, 2002
Several distinguishing features of fish can be used to tell apart the various species; however, some practice is required in the use of these features to separate closely related members such as species in the salmonid (trout) family. The technique used is referred to as "eyeballing fish" — species identification at a glance based on simple criteria such as body form, body structures and coloration. Anglers will find that the eyeballing technique works easiest for identifying fish families and sport fish species. For non-sport species and uncommon sport fish species, the detailed keys given in the book The Fishes of Alberta are recommended.
Dichotomous Fish Keys
"Dichotomous" means a division into two parts or branching by repeated divisions. That is how a fish "key" is designed to identify fish into separate groups and then as individual species. To learn more about how fish keys work, examine the following exercises using a deck of playing cards.
Excercise One:
Spread a deck face up in a pile and separate its four "species" of cards by using the "key" below — follow the steps one step at a time:
Key to Separate Playing Cards:
Exercise Two:
Pick a card from the deck, any card. Now identify the "species" of card using the above key step by step. Repeat with additional cards. After a few practice
