Pleas person expresses on catching fish (7)
I believe the answer is:
prayers
'pleas' is the definition.
(pleas to God)
'person expresses on catching fish' is the wordplay.
'expresses' is a deletion indicator (some letters are pressed out).
'catching' means one lot of letters goes inside another.
'fish' becomes 'ray' (ray is a kind of fish).
'person' with 'on' taken out is 'pers'.
'pers' going around 'ray' is 'PRAYERS'.
(Other definitions for prayers that I've seen before include "Occasion for worship" , "Orisons" , "Appeals to a deity" , "Requests to God" , "Communications to a deity" .)