Captain Fish, backing scripture, to hold on (5,2)
I believe the answer is:
cling to
'hold on' is the definition.
(thesaurus)
'captain fish backing scripture' is the wordplay.
'captain fish' becomes 'cling' (I can't justify this - if you can you should believe this answer much more).
'backing' is a reversal indicator.
'scripture' becomes 'OT' (Old Testament).
'ot' written backwards gives 'to'.
'cling'+'to'='CLING TO'
'to' acts as a link.
Can you help me to learn more?
(Another definition for cling to that I've seen is " Grip".)