Fish streams (4)
I believe the answer is:
rays
This clue is a double definition.
'fish' is the first definition.
(I've seen this before)
'streams' is the second definition.
(ray can mean a stream or beam)
(Other definitions for rays that I've seen before include "Beams - fish" , "we hope to catch occasionally out of the blue?" , "Straight lines extending from a point" , "Single lines of light" , "Columns of light or heat" .)