With limits of barrier removed, fish intrude beyond boundaries (8)
I believe the answer is:
encroach
'with limits of barrier removed' is the definition.
I can't tell whether this defines the answer.
'fish intrude beyond boundaries' is the wordplay.
I cannot quite see how this works, but
'fish' could be 'roach' (roach is a kind of fish) and 'roach' is present in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for encroach that I've seen before include "Advance beyond proper limit" , "Enter upon another's property or rights" , "Impinge, infringe" , "'Trespass, infringe (8)'" , "Tread on someone's toes" .)