That is a plainfin midshipman, Porichthys notatus. They are primarily midwater fish but they breed in the intertidal and nearshore subtidal in the summer. Males guard a hole in which the females lay large eggs. The males guard the egg until they hatch. Males can thrum their swimbladder to attract females. This has led people who live on houseboats (for example, in San Francisco bay, to complain to the authorities that some type of construction is going on. They are called midshipmen because they have a double line of light organs along the belly. The light organs provide light that matches the light coming from above; this camouflages the fish. However, our fish do not glow (though they have the structure) because our area lacks an ostracod (marine crustacean) that actually makes the substrate that creates light. You can read more about this very interesting fish here: http://en.wikipedia.org/wiki/Porichthys_notatus.