Fishy weapon? (4)
This clue is a double definition.
'fishy' is the first definition.
(type of fish)
'weapon?' is the second definition.
(pike is a kind of weapon)
(Other definitions for pike that I've seen before include "Weapon on long shaft; Northern hill" , "Fish - medieval weapon" , "Fish - old infantry weapon" , "Old weapon -- Dad's Army character" , "Position of one diving" .)
'fishy weapon?' is the definition.
I know nothing about this answer so I can't tell whether this works.
'fishy weapon?' is the wordplay.
'fishy' becomes 'ray' (type of fish).
'weapon?' becomes 'gun' (gun is a kind of weapon).
'ray'+'gun'='RAY-GUN'
(Other definitions for ray gun that I've seen before include "Sci-fi weapon" , "Star Wars weapon" , "Science fiction weapon" .)