Act of devotion, through catching fish (6)
I believe the answer is:
prayer
'act of devotion' is the definition.
'through catching fish' is the wordplay.
'through' becomes 'per' (I've seen this in another clue).
'catching' indicates putting letters inside.
'fish' becomes 'ray' (ray is a kind of fish).
'per' enclosing 'ray' is 'PRAYER'.
(Other definitions for prayer that I've seen before include "Litany" , "request for help?" , "One offered in church" , "Words to a deity" , "Entreaty to deity" .)