What’s that fish? The (dichotomous) key to fish identification
Students, anglers and everyone else can use a simple dichotomous key to answer the question, “What’s that Fish?”
November 11, 2014 - Author: Steve Stewart, Michigan State University Extension, Michigan Sea Grant
The Great Lakes region is home to an impressive variety of fish, numbering more than 160 separate species. A species consists of individuals that share t
he same gene pool and can interbreed. These species belong to 28 major fish families. A family is a taxonomic group that includes similar species.
Many of us who live in the Great Lakes are familiar with fish in the sunfish and bass family, cold-water species in the salmon and trout family, or some of the 62 species that make up the minnow family. But ancient fish, such as lake sturgeon and longnose gar, also inhabit waters of the Great Lakes region and possess unique attributes that have allowed them to survive for millions of years. With the exception of some primitive species, most fish have common characteristics that include gills, scales, fins and bony skeletons. Some characteristics that differentiate fish include the shape of their heads, where their mouths are located, fin type and location, and average adult size.
Color markings, such as vertical stripes or fin spots, may also help differentiate fish when used in combination with other factors including geographic range. Distinguishing characteristics can provide clues about where a species typically lives and what it eats.
For example, fish in the sturgeon and sucker families have downward-oriented mouths (sometimes called ventral) that enable them to find food along a lake or stream bottom. Other traits, such as fin shape and location, can provide clues about whether a fish is generally a fast swimmer or a slow swimmer.
To correctly identify fish and classify newly discovered species, fisheries scientists use a dichotomous key based on distinguishing characteristics. A dichotomous key is a classification tool used to sort, organize and identify a collection of objects or living organisms. The key is mad
e up of a series of questions with two choices, such as “Are the scales small or large?” Each choice leads to another question.
By making choices and progressing logically through the key, users follow a path that ends with the correct identification of the organism. Michigan Sea Grant has developed the lesson Can I See Some ID Please? How to Identify Fish as part of the Teaching Great Lakes Science collection of online lessons, collaboratively developed with Michigan State University Extension. By using their knowledge of distinguishing characteristics and a simplified key, students use full-color illustrations of fish to work through the key and make identifications among 10 Great Lakes fish families. You can do the same!
