In part of fish I note space (8)

I believe the answer is:

infinite

'space' is the definition.
(I know that space can be written as infinite)

'in part of fish i note' is the wordplay.
'part of fish' becomes 'fin' (fish have fins).
'note' becomes 'te' (musical note).
'in'+'fin'+'i'+'te'='INFINITE'

(Other definitions for infinite that I've seen before include "Never-ending" , "Everlasting" , "Without limit" , "Unlimited" , "Having no limits in time, space etc." .)

I've seen this clue in The Sun.

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