STUDENT LABORATORY — Using a Dichotomous Key to Identify ...
STUDENT LABORATORY ¡ª Using a Dichotomous Key to Identify New York State
Freshwater Fishes
Full Name: ___________________________________________
Lab Date: __________
Lab Section: _______ Lab Instructor: _____________________
Credit: 1 lab
Standards:
? Common Core Standards: Reading (Grade 9): 3,4,5
? Living Environment Core Curriculum: LE Lab checklist: ¡°Designs and uses dichotomous keys to
identify specimens.¡±
Objectives: Students will be able to:
? Use a dichotomous key to identify fish native to New York State.
Portions of this lab were adapted from dichotomous key labs from Mr. Comet, a teacher at South Lewis High School in Turin, NY and Ms. Foglia from
Division Avenue High School, Levittown.
Pre-Lab:
In taxonomy, a traditional dichotomous key
(sometimes called a single-access key) is used to
sort and classify the diversity of organisms by
physical characteristics. Now, with scientific
advancements, other characteristics such as
genetic similarities can be added to a key as well.
To use a dichotomous key, one answers a series
of questions, each with either a yes or a no
answer. Each answer leads to another numbered
question where we make another yes or no
decision. This continues until the last question
which reveals the identity of our organism.
An example of a dichotomous key in flow-chart
format is shown here. This simple guide can be
used to identify an insect, dog, snail or a worm.
Snail
Insect
Worm
Dog
In this lab, you will use a dichotomous key to identify New York State freshwater fish, and first must familiarize
yourself with fish anatomy. Watch the video, pause at 0:55 and see how many numbered parts you can label in
the table below. Use the anatomical terms (and not the labeled fish diagram!) listed on the next page for help.
Watch ¡°A Quick Lesson on External Fish Anatomy¡± ¨C
Un-pause the video and see how you did.
Afterwards, watch for another short video about fish anatomy.
Number
from Video
1
2
3
4
5
6
7
8
9
10
11
12
Anatomical Name
Image:
Prime Time Aquatics
Review the anatomical terms, descriptions and the diagrams below and reference them as needed as you identify
each fish using the dichotomous key.
? Anterior: towards the head
? Posterior: Towards the back
? Broad part of the fish: height of thickest part of the fish from top to bottom, not including the fin. Use a
ruler to measure the broad part, then use a ruler to measure the length of the fish. Compare the two
numbers as a ratio. See image below.
? Hinge: Where the corners of the mouth meet; can be in front of the eye, below the eye, or in back of the
eye.
? Barbel: a fleshy projection from the lip or head (like on a catfish)
? Concave: curving inward
? Fins: Fins can be single (separate), elongated (one type of fin, for example a dorsal fin that stretches
along part of the length of the body) or continuous (cannot distinguish separate fins, stretch along the
entire length of fish as one fin)
o Adipose: a small fin on the top mid-line of the body near the tail fin (not pictured below).
o Anal: a fin along the lower mid-line of the body near the tail fin.
o Caudal: tail fin. Can be forked: looks like a sideways ¡°V¡±, partially forked or un-forked.
o Dorsal: the fin or fins along the top mid-line of the body.
o Pectoral: the paired fins nearest the head, corresponding to front legs or arms.
o Pelvic: the paired fins nearest the tail, corresponding to hind legs.
? Scales: overlapping outgrowths of the skin.
How to measure the ¡°broad¡± (top to
bottom arrow) part of the fish as
compared to the length of the fish (left to
right arrow).
--------------------------------------------------------------Laboratory Exercise----------------------------------------------------------
Procedure/Observations:
1. Watch this short video to learn how to use a dichotomous key:
2. Closely examine fish 2 on the New York State Fish sheet.
3. Refer to the Dichotomous Key on the next page. Note that each numbered item on the key presents two
possibilities.
4. Read statements 1a and 1b in the Dichotomous Key. One of these statements describes a characteristic of
fish 2, while the other does not.
5. Since fish 2 has no scales (or at least none that we can see), we choose 1b which now refers us to number
12.
6. Read the 12a and 12b descriptors. This fish is not elongated or snakelike. Go to number 13.
7. Read the descriptors for 13a and 13b. The fish we are classifying has barbels growing from its lips and the
top of its head. Go to number 14 of the key.
8. 14b describes a fish having a caudal fin that is rounded with a blunt head. We see that this is the Bullhead
catfish. Go to the page with the New York State Fish Identification table. Under the column ¡°Identified as¡±
write ¡°Bullhead catfish.¡± In the column labeled ¡°Identification pathway¡± write ¡°1b, 12b, 13a, 14b¡±
9. Identify the remaining fish using the dichotomous key. Terms on the dichotomous key that are in bold are
defined above. Note: identification is challenging! Do your best!
Dichotomous Key for Common Freshwater Fish of New York State
No.
1a.
1b.
2a.
2b.
3a.
3b.
4a.
4b.
5a.
5b.
6a.
6b.
7a.
7b.
8a.
8b.
9a.
9b.
10a.
10b.
11a.
11b.
12a.
12b.
13a.
13b.
14a.
14b.
15a.
15b.
16a.
16b.
17a.
17b.
Statement
Body noticeably covered with scales
Scales not covering body or too small to be seen
Dorsal fin single
Dorsal fins two or more, joined or separated
Body more than four times as long as broad; front edge of dorsal fin
far back on body; mouth large, hinge of mouth in back of eye
Body less than four times as long as broad; front edge of dorsal fin
about midway between head and tail; mouth not large, hinge in front
of eye.
Dark lines forming netted design on body: fins not spotted
Body covered with yellow spots; fins spotted
Mouth turned downward: barbels absent; dorsal fin not elongated
Mouth not turned downward: barbels present; dorsal fin elongated
Two dorsal fins separated, the anterior spiny and the posterior soft
(not spiny)
Two dorsal fins united, forming an anterior spiny portion and a
posterior soft portion
Top of head concave, farming a hump in front of dorsal fin; dark
vertical bars on body
Top of head not concave, body sloping to dorsal fin and not forming a
hump; dark blotches on body
Body more than three times as long as broad
Body less than three times as long as broad
Hinge of jaws behind the eye: notch between spiny and soft dorsal fin
deep and nearly separating into two fins
Hinge of jaws below the eye; notch between spiny and soft dorsal fin
not nearly separating into two fins
Mouth large, hinge below or behind eye
Mouth small, hinge in front of eye
Five to seven spines in dorsal fin; dark spots forming broad vertical
bars on sides, Red/orange earspot on gill covering (see picture)
Ten or more spines in dorsal fin: sides flecked with dark spots
Body elongated and snakelike: dorsal, caudal, and anal fins
continuous (cannot distinguish separate fins)
Body not elongated and snakelike: dorsal, caudal, and anal fins
separate; adipose fin present
Barbels growing from lips or top of head; head large and broad
Barbels lacking; head not large and broad
Caudal fin deeply forked(looks like a sideways ¡°v¡±); head tapering
Caudal fin rounded or slightly indented but not forked: head blunt
Dorsal fin rounded at top: body silvery, speckled with black markings
Dorsal fin long and pointed at top: body bluish-gray without speckles
Caudal fin deeply forked; back not mottled (spotted) or with few
spots
Caudal fin square or slightly indented; back mottled or spotted
Back and caudal fin spotted: broad horizontal band along sides
Back mottled with dark lines: caudal fin not spotted; fins edged with
white
Go to/Identify
2
12
3
6
4
5
Pickerel
Northern Pike
White Sucker
Carp
7
8
Yellow Perch
Walleye
9
10
Large Mouthed
bass
Small Mouthed
Bass
11
Bluegill
Pumpkinseed
Rock Bass
American Eel
13
14
16
15
Bullhead Catfish
Channel Catfish
Blue Catfish
Atlantic Salmon
17
Rainbow Trout
Brook Trout
New York State Fish Identification Table
Fish
Identified as
Identification pathway
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Analysis and Conclusion:
1. What did you struggle with as you used the dichotomous key to identify the NYS fish?
*Note ¡ª This lab is due at the end of the lab period or as directed by your instructor. Your instructor may modify the lab based on time.
New York State Fish
Fish 1
Fish 2
Fish 3
Fish 4
Fish 5
Fish 6
Fish 7
Fish 8
Fish 9
Fish 10
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