Page "Fish anatomy" Paragraph 26

In bony fish, most fins may have spines or rays.

A fin may contain only spiny rays, only soft rays, or a combination of both.

If both are present, the spiny rays are always anterior.

Spines are generally stiff and sharp.

Rays are generally soft, flexible, segmented, and may be branched.

This segmentation of rays is the main difference that separates them from spines ; spines may be flexible in certain species, but they will never be segmented.