Travelling at high speed injured a fish (8)
I believe the answer is:
hurtling
'travelling' is the definition.
(hurtling is a kind of travelling)
'injured a fish' is the wordplay.
'injured' becomes 'hurt' (similar in meaning).
'a fish' becomes 'ling' (ling is a kind of fish).
'hurt'+'ling'='HURTLING'
'at high speed' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for hurtling that I've seen before include "going fast" , "plunging" .)