Depressed with healthy marine animal (4,5)
I believe the answer is:
blue whale
'marine animal' is the definition.
The definition and answer can be both animals as well as being singular nouns.
Maybe you can see an association between them that I don't see?
'depressed with healthy' is the wordplay.
'depressed' becomes 'blue' (I've seen this before).
'with' becomes 'w' (short for with).
'healthy' becomes 'hale' (hale can mean fit and healthy).
'blue'+'w'+'hale'='BLUE WHALE'
Can you help me to learn more?
(Other definitions for blue whale that I've seen before include "World's largest mammal" , "Largest living animal" , "there's nothing bigger" , "World's largest animal" .)