Sample Flow Chart Dichotomous Key Classification Webquest


Example flow chart

EXAMPLE of a Dichotomous Key for the Classification
of Some Common Fish
How to use this key.  Always start at number 1. Read both 1 a and 1 b.  Choose the description which best matches your fish and follow the directions to move to the next description.  Each description has two choices.  Each description will lead you to either another description or to the name of the fish.  The linked  pages will illustrate the various characteristics used in this key.

1a Body noticeably covered with scales  **Go to 2
1b Scales not covering body or too small to be seen  ** Go to 12

2a Dorsal fin single  ** Go to 3
2b Dorsal fins two or more, joined or separated  ** Go to 6

3a Body  more than four times as long (front to back) as deep (top to bottom); the front edge of dorsal fin starts far back on body; the is mouth large, the hinge of the mouth starts in back of eye  ** Go to 4
3b Body less than four times as long (front to back) as deep (top to bottom); front edge of dorsal fin starts about halfway between head and tail; mouth not large, hinge of the mouth is in front of eye  ** Go to 5

4a Dark lines forming netted design on body; fins not spotted.  ** Pickerel
4b Body covered with spots; fins spotted   **  Northern pike

5a Mouth turned down; barbels absent; dorsal fin not elongated   ** White Sucker
5b Mouth not turned downward; barbels present; dorsal fin elongated   ** Carp

6a Two dorsal fins separated, the anterior spiny and the posterior soft.  ** Go to 7
6b Two dorsal fins united, forming an anterior spiny portion and a posterior soft portion  **Go to 8

7a Top of head concave, forming a hump in front of dorsal fin; dark vertical bars on body  ** Yellow perch
7b Top of  head not concave, body sloping to dorsal fin and not forming a hump; dark blotches on body ** Walleyed pike

8a Body more than three times as long as broad  ** Go to 9
8b Body less than three times as long as broad  ** Go to 10

9a Hinge of jaws behind the eye; notch between spiny and soft dorsal fin deep and nearly separating into two fins  ** Largemouth black bass
9b Hinge of jaws below the eye; notch between spiny and soft dorsal fin not nearly separating into two fins  ** Smallmouth black bass

10a Mouth large, hinge below or behind eye  ** Go to 11
10b Mouth small, hinge in front of eye  ** Bluegill

11a Five to seven spines in dorsal fin; dark spots forming broad vertical bars on sides  ** White crappie
11b Ten or more spines in dorsal fin; sides flecked with dark spots  ** Rock bass (Redeye)

12a Body much elongated and snakelike; dorsal, caudal and anal fins continuous  ** Eel
12b Body not elongated and snakelike; dorsal, caudal, and anal fins separate; adipose fin present  ** Go to 13

13a Barbels growing from lips and top of head; head large and broad  ** Go to 14
13b Barbels lacking; head not large and broad  ** Go to 16

14a Caudal fin deeply forked; head tapering  ** Go to 15
14b Caudal fin rounded or slightly indented but not forked; head blunt  ** Bullhead catfish

15a Dorasl fin rounded at top; body silvery, speckled with black markings  ** Channel catfish
15b Dorsal fin long and pointed at top; body bluish gray without speckles  ** Blue catfish

16a Caudal fin deeply forked; back not mottled and with few spots  ** Atlantic salmon
16b Caudal fin square or slightly indented; back mottled or spotted  ** Go to 17

17a Back and caudal fin spotted; broad horizontal band along sides  ** Rainbow trout
17b Back mottled with dark lines; caudal fin not spotted; fins edged with white  ** Brook trout