Fish regularly sense ciphers (5)
I believe the answer is:
codes
'ciphers' is the definition.
('code' can be a synonym of 'cipher')
'fish regularly sense' is the wordplay.
'fish' becomes 'cod' (cod is a kind of fish).
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
The alternate letters of 'sense' are 'es'.
'cod'+'es'='CODES'
(Other definitions for codes that I've seen before include "Sets of rules or cryptograms" , "morals" , "Word systems devised to create secrecy" , "System of letters etc for the purpose of secrecy" , "Ciphers" .)