Fish like cod don't have tails cut up (7)
I believe the answer is:
pollack
'fish like cod' is the definition.
'pollack' can be an answer for 'fish' (I've seen this before). I am not certain of the 'like cod' bit.
'don't have tails cut up' is the wordplay.
'don't have' becomes 'lack' (I've seen this in another clue).
'tails' says to put letters next to each other (tail can mean to follow).
'cut up' becomes 'pol' (I can't justify this - if you can you should give a lot more credence to this answer).
'lack' after 'pol' is 'POLLACK'.
Can you help me to learn more?
(Another definition for pollack that I've seen is " Food fish of the cod family".)