Bloke thanks journalist Martin for big fish (5,3)

I believe the answer is:

manta ray

I'm a little stuck... Click here to teach me more about this clue!

'big fish' is the definition.
'manta ray' can be an answer for 'fish' (I've seen this before). I'm not sure about the 'big' bit.

'bloke thanks journalist martin' is the wordplay.
'bloke' becomes 'man' (informal term for a man).
'thanks' becomes 'ta' (UK informal version of 'thank you').
'journalist martin' becomes 'ray' (I can't justify this - if you can you should give a lot more credence to this answer).
'man'+'ta'+'ray'='MANTA RAY'

'for' is the link.

Can you help me to learn more?

(Other definitions for manta ray that I've seen before include "Devilfish" , "large fish" .)

I've seen this clue in the Sydney Morning Herald.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.