Tropical coasts contain green fish (5)
I believe the answer is:
trawl
'fish' is the definition.
(trawling is a kind of fishing)
'tropical coasts contain green' is the wordplay.
'tropical coasts' becomes 'tl' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'contain' indicates putting letters inside.
'green' becomes 'raw' (synonyms).
'tl' going around 'raw' is 'TRAWL'.
Can you help me to learn more?
(Other definitions for trawl that I've seen before include "Fish commercially with nets" , "seek suitable candidates" , "Use net" , "Fish by dragging bag-net along sea bed" , "Catch" .)