Fish that's the last of its kind? (4)
I believe the answer is:
sole
'fish' is the definition.
(I know that sole is a type of fish)
'the last of its kind?' is the wordplay.
'the last of' suggests the final letters.
'kind?' becomes 'ole' (I can't justify this - if you can you should believe this answer much more).
The last letter of 'its' is 's'.
's'+'ole'='SOLE'
'that's' acts as a link.
Can you help me to learn more?
(Other definitions for sole that I've seen before include "Lone; part of foot" , "Bottom of the foot" , "Unique" , "A lonely sort of flatfish" , "swimmer" .)