A fishy, motley rabble (6)
I believe the answer is:
barbel
'a fishy motley rabble' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'motley rabble' is the wordplay.
'motley' indicates an anagram (motley can mean varied or different).
'rabble' anagrammed gives 'BARBEL'.
Can you help me to learn more?
(Other definitions for barbel that I've seen before include "swimmer" , "catfish feature" , "fish" .)