Question

refer to this portion of a dichotomous key for fish identification to answer the question.

1. (a) has a single dorsal fin ® 5

(b) has a double dorsal fin ® 2

1. (a) has small fin on back near tail ® 6

(b) has no fin on back near tail ® 7

1. (a) has barbs near the mouth ® catfish

(b) does not have barbs near the mouth ® 10

according to this dichotomous key, any catfish must have
a double dorsal fin, a small fin on the back near the tail, and barbs near the mouth.
a single dorsal fin, no small fin on the back near the tail, and barbs near the mouth.
a double dorsal fin, a small fin on the back near the tail, and no barbs near the mouth.
a single dorsal fin, a small fin on the back near the tail, and barbs near the mouth.

Explanation:

To determine the characteristics of a catfish, we follow the dichotomous key:

1. Catfish identification starts at step 6(a), which refers back to step 5(a), then step 1(a):

• Step 1(a): Has a single dorsal fin (leads to 5).
• Step 5(a): Has a small fin on back near tail (leads to 6).
• Step 6(a): Has barbs near the mouth (identifies Catfish).

Thus, catfish must have a single dorsal fin, a small fin on the back near the tail, and barbs near the mouth.

Answer:

D. a single dorsal fin, a small fin on the back near the tail, and barbs near the mouth.