Fish from the lighthouse (3)

I believe the answer is:

ray

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'fish' is the definition.
(ray is a kind of fish)

I cannot understand how the rest of the clue works.

(Other definitions for ray that I've seen before include "Flatfish or sunbeam" , "Sunbeam or flat fish" , "Beam of light or flat fish" , "Shaft of light" , "may be electric" .)

I've seen this clue in the Evening Standard.

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